New Methodology for the Synthesis of Furans, Pyrrolidines, and 1,3

K): Reagents with various synthetic applications. Jörg Kühn , Karola Rück-Braun. Journal für Praktische Chemie/Chemiker-Zeitung 1997 339 (1), 675-...
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Organometallics 1996,14, 4710-4720

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New Methodology for the Synthesis of Furans, Pyrrolidines, and 1,3=PolyolsUsing Allyl(cyclopentadienyl)iron(II) Dicarbonyl Complexes Songchun Jiang, Ti Chen, and Edward Twos* Department of Chemistry, State University of New York at Buffalo, Amherst, New York 14260 Received October 26, 1994@ Synthetic methodology is reported for the preparation of 1,3-polyols, tetrahydrofurans, and pyrrolidines based on the Lewis acid-promoted reaction of allyl(cyclopentadieny1)iron dicarbonyl with aldehydes, ketones, and imines. The initial products of these additions are zwitterionic iron-olefin x-complexes, which can be further utilized for the construction of either acyclic (polyol) or heterocyclic (furan, pyrrolidine) structures. Methoxide and primary alkoxides add to the internal alkene center of the n-complex in a regiospecific manner to give (P-alkoxyalky1)iron complexes, which upon stirring in methanolic ceric ammonium nitrate solution and subsequent reduction with lithium borohydride give 1,3,5-triol derivatives. Alternatively, treatment of the zwitterionic x-complex with potassium tert-butoxide in CHzCl2 leads to formation of the furan cycloadduct by intramolecular addition of the homoallylic alkoxide to the cationic n-complex. The [3 21-cycloaddition reaction of the allyliron complex with the carbonyl compound can also be executed, without isolation of the intermediate iron-olefin n-complex, using a Lewis acid catalyst. Similarly, N-tosylimines can be employed in the [3 21-process for the synthesis of pyrrolidine esters. Of the catalysts 21-reactions involving aldehydes or examined, ZnCl2 gives the best results for [3 N-tosylimines, while Tic4 is preferred for the ketone cycloadditions. The allyliron-carbonyl [3 21-annulations can be effected in intramolecular fashion to provide multicyclic fused furan rings in a single synthetic operation.

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Introduction In the preceding article,l a new allylation procedure was described based on the BFs-promoted reaction of allylic (cyclopentadieny1)irondicarbonyl complexes2with aldehyde^,^ ketone^,^ imine^,^ and acetals.6 The unusual feature of this methodology is the fact that the product of the reaction retains the metal moiety in the form of a zwitterionic iron-olefin n-complex (structure 2). These investigations have explored the scope and

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limitations of this reaction and provided detailed structural information about the n-adducts produced in the allylation. In this paper, we present o u r studies on the intermolecular and intramolecular reactions of these n-complexes with primary alkoxides and the extension of this methodology to the [3 21-cycloadditions of allyliron complexes with carbonyl compounds and imines. As a consequence of strong electron-withdrawal by the electropositive metal center, the alkene centers of cationic olefin-Fe(CO)sCp complexes 3 are rendered highly

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@Abstractpublished in Advance ACS Abstracts, August 15,1995. (1)Jiang, S.; Agoston, G. E.; Chen, T.; Cabal, M.-P.; Turos, E. Organometallics 1995,14, 4697. (2)Green, M.L. H.; Nagy, P. L. I. J . Chem.Soc. 1963,189. (3)Agoston, G.E.;Cabal, M. P.; Turos, E. Tetrahedron Lett. 1991, 32,3001.This procedure provides the zwitterionic n-complex which is often contaminated with variable amounts of a co-adduct that is difficult to remove and which diminishes the efficiency of the cyclization step. This complex appears to be Fe(CO)ZCp(CHz==CHCH3)+-BF4from comparison of its lH-, l3C-, and 19F-NMR data to that of an authentic sample (ref 14, preceding paper). To minimize the formation of this impurity, an excess of the aldehyde or ketone is typically used in the allylation reaction. (4) Jiang, S.; Turos, E. Tetrahedron Lett. 1991,32,4639. (5) Chen, T.; Jiang, S.; Turos, E. Tetrahedron Lett. 1994,35,8325. (6) For accounts of the chemistry of organoiron carbonyl compounds: (a) Fatiadi, A. J . J . Res. Nut. Inst. Stand. Technol. 1991,96, 1. (b) Rosenblum, M. J . Organomet. Chem. 1986, 300, 191. (c) Rosenblum, M. Acc. Chem. Res. 1974, 122. (d) Astruc, D. Use of Organoiron Compounds in Organic Synthesis. In The Chemistry ofthe Carbon-Metal Bond; Hartley, F. R., Ed.; , Wiley: New York, 1987;Vol 4,Chapter 7,pp 625-731.

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susceptible toward nucleophilic a t t a ~ k .Rosenblum8 ~ and Busettoghave independently examined the addition of heteronucleophiles and carbon nucleophiles to cationic (7)For reviews, see: (a) Pearson, A. J. Transition Metal-Stabilized Carbocations in Organic Synthesis. In The Chemistry of the CurbonMetal Bond; Hartley, F. R., Ed.; Wiley: New York, 1987; Vol. 4, Chapter 10, pp 889-980. (b) Davies, S.G.; Green, M. L. H.; Mingos, D. M. P. Tetrahedron 1978,34,3047. (8)(a)Rosan, A. M.; Rosenblum, M.; Tancrede, J. J . Am. Chem. SOC. 1973,95,3062. (b) Lennon, P.; Madhavarao, M.; Rosan, A,; Rosenblum, M. J . Organomet. Chem. 1976,108, 93.(c) Klemarczyk, P.; Price, T.; Priester, W.; Rosenblum, M. J.Organomet. Chem. 1977,C25,139.(d) Lennon, P.; Priester, W.; Rosan, A. M.; Madhavarao, M.; Rosenblum, M. J . Orgunomet. Chem. 1977,C29,139.(e)Turnbull, M. M.; Foxman, B. M.; Rosenblum, M. Organometallics 1988,7,200.(f) Begum, M.K.; Chu, K.-H., Coolbaugh, T. S.;Rosenblum, M.; Zhu, X.-Y. J. Am. Chem. SOC.1989,111, 5252. (9)Busetto, L.;Palazzi, A.; Ros, R.; Belluco, U. J. Organomet. Chem. 1970,25,207.

0276-7333/95/2314-4710$09.00/0 0 1995 American Chemical Society

Allyl(cyclopentadienyl)iron(II) Dicarbonyls

Organometallics, Vol. 14, No. 10, 1995 4711

Scheme 1

-

1)'BuMe2sicI pmine,DMAP

UBH,

THF,RT

%uMe2Si0

OR

OAc

2) AQO, pyridine

0

9

a R = Ph; R' =CH3

isolated yields, dlastereomeric ratios (8) (0) (65%+ 24% bis-siiyiatedproduct) (55%, 1 .l:i)

b R = 3-NOZ-Ph; R = CHI

(53%,1.2:1)

(83%)

R = 4-NOz-Ph;R' = CH3

(47%, 1 .I :I)

(77Vot 2Y0bls-silylatedproduct + 3% recoyeredalwhd)

C

d R = (CH&CH3; R' = CHa

(30%,1.1 :1) (70%)

e R .iCNOZ-Ph; R' = CHzPh

(22%,1.311) (70%)

I f R = CNOz-Ph; R' = CHzCH=CHz

(m%, 1.1 :1) (64%)

iron-olefin n-complexes and showed that the nucleophile attacks the olefin from the face opposite the metal group to afford /3-substituted alkyliron complexes 4. While these additions generally work well for complexes of ethylene, propylene, or enol ethers, reactions involving more highly functionalized olefin complexes are often plagued by competitive processes such as allylic deprotonation, electron transfer, or attack of the nucleophile on the metal center. Concerned about this, we therefore set out to study the efficiency and regiochemical selectivity for the nucleophilic addition of alkoxides to zwitterionic n-complexes 5. Our initial attempts t o add methoxide ion to n-complexes 53using the published protocol^^^^^ gave demetalated material as the only discernible product. Eventually, satisfactory conditions were found for adding methoxide ( R= CH3) and primary alkoxides ( R= CH2Ph, CH2CH=CH2) to 5 t o give (P-alkoxyalkyl)ironcomplexes 6 (Scheme 1). Because of their apparent instability, these crude a-complexes6 were treated immediately with methanolic Ce(NH&(NO& at low temperatwelo under an atmosphere of CO'l to transform the iron group to a methyl ester.12 Evaporation and flash chromatography of the crude residue gave a separable mixture of hydroxy esters 7 and their &lactones, which upon reduction with LiBH4 in THF13 afforded diols 8. Overall yields (from the aldehyde used to prepare 5) and diastereomeric ratios of diols 8 are shown in Scheme l . 1 4 Diols 8 can be converted to triol derivatives 9 by monosilylation (TBSC1, DMAP) of the primary alcohol ~~

(10)When the oxidative CO insertion reaction is conducted at room temperature, only the demetalated homoallylic alcohol is obtained. It appears that lower temperatures disfavor the demetalation pathway and allow the esterification procedure to occur more cleanly. Reger and Mintz have observed a similar phenomenon for Ce(IV)-promoted oxidative CO insertion (Reger, D. L.; Mintz, E. Organometallics 1984, 3, 1759). (11)(a) Nicholas, K.M.; Rosenblum, M. J . Am. Chem. SOC.1973, 95,4449. (b) Anderson, S.N.; Fong, C. W.; Johnson, M. D. J . Chem. SOC.,Chem. Commun. 1973, 163. (c) Bock, P. L.; Boschetto, D. J.; Rasmussen, J. R.; Demers, J. P.; Whitesides, G. M. J . Am. Chem. SOC. 1974,96,2814. (12)Other common oxidants such as CuC12, Brz, and 0 2 were also tried without success, with the homoallylic alcohol being obtained in each case. (13)The use of LWH4 results in reduction of the nitro group for the nitrophenyl substrates.

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followed by acetylation (Ac20, neat pyr) of the secondary hydroxyl group. The combined yields for these two steps are also listed in Scheme 1. The lack of diastereoselectivity of these transformations can be traced back to complex 5, which is formed in the BFs-promoted allylation reaction of complex l and aldehyde as a nearly equal mixture of facial isomers.' For characterization purposes, the individual diastereomers of 9e,9f were separated by flash chromatography, but no attempt was made to assign their sydanti stereochemistry. The complete regiochemical selectivity observed for these alkoxide additions to 5 agrees with Rosenblum's earlier findings that oxygen nucleophiles add t o cationic Fe(C0)zCp n-complexes of terminal olefins exclusively a t the internal carbon center, apparently due to thermodynamic considerations.8b We also find it noteworthy that the oxidative carboxylation of allyliron complexes 6 produces esters 7 cleanly despite the opportunity for 6 to undergo facile, acid-catalyzed/3-elimination.15 During the course of these studies, we discovered that n-complexes 2 can be converted to tetrahydrofurans by treatment with KOtBu in an uprotic solvent such as CH2Cl2 (Scheme 2). The progress of the cyclization can be monitored spectroscopically16by observing the disappearance of the CO infrared stretching bands a t 2075 and 2035 cm-l (for n-complex 2) and the appearance of new signals a t 2000 and 1945 cm-l (for a-complex 10). Iron furans 10 were converted directly to furan esters 11 with methanolic ceric ammonium nitrate. Overall yields of 11 from 2 are about 45%for complexes derived from aldehydes (lla-c), and around 20% for those prepared from ketones (lld,e). Roughly equal amounts of diastereomeric cycloadducts 11 are obtained in these (14)If the esterification reaction is allowed to proceed for several days, dimethyl ether adducts are formed as a result of acid-catalyzed etherification of the benzylic alcohol in 7.These compounds have been characterized on the basis of their lH NMR spectra, which show two methoxy ether signals near 6 3.3 and a singlet at 6 3.7for the methyl ester. Each signal is a doublet, which indicates that the two diastereomers are formed in equal amounts. (15)Erlacher, H. A,; Turnbull, M. M.; Chu, K.-H.; Rosenblum, M. J . Org. Chem. 1989,54,3012. (16)rll-Allyliron dicarbonyl reagents show CO absorbances around 2010 and 1950 cm-1, whereas y2-iron-olefin complexes characteristically absorb near 2070 and 2030 cm-l.

Jiang et al.

4712 Organometallics, Vol. 14, No. 10, 1995 base-promoted cyclization reactions, which is expected since n-complexes 2 are utilized as equimolar mixtures of facial is0mers.l These intramolecular alkoxide additions to the cationic Fe(C0)zCp-olefin complexes offer ready access to tetrahydrofurans from carbonyl precursors. Thus, this allylation-cyclization procedure is analogous to those previously observed in reactions of 1 with activated

Scheme 2

Yields, transxis ratio of furans 11

1

1.5:l) a R=H, R'=Ph (a%,

double bond compounds X=Y,6 which are thought to proceed through the intermediacy of a dipolar intermediate. However, only one example of such a process involving a carbonyl substrate has been reported. To summarize, alkoxides add to the zwitterionic n-complexes 5 in a regiospecific manner to afford (balkoxyalky1)iron complexes. Depending on whether a protic or aprotic solvent is employed, these additions can be directed t o occur through either an intermolecular or intramolecular mode to provide acyclic (polyol) or cyclic (furan) derivatives, respectively (Scheme 3). Lewis Acid-Catalyzed[3 21-Reactions. Despite the fact that furans are important structural subunits within numerous natural products and pharmaceutical agents, few methods have been reported for the direct formation of five-membered oxygen rings via the [3 21-coupling of a 1,3-carbon dipole with a carbonyl compound (eq l).17 In contrast, the analogous [4+21-

b R-H, R'9-NOzPh (a%, 1.21) C

R=H, R'9-CH30Ph (G%, 1.2:l)

d R=R'=(CH& (19%)

e R=CH,, R'=Ph (20%, 1.5:l)

To test this possibility,we first examined the reaction of 4-nitrobenzaldehyde with allyliron reagent 1 under

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MeO\ U

111 Ar=4-N02Ph

a variety of conditions using 15 mol % of catalyst. As above, the iron furan cycloadduct was converted directly to the methyl ester l l f (R = H, R = 4-NOzPh) using methanolic ceric ammonium nitrate. Of the Lewis acids probed to catalyze the [3 21-reaction (Table l),ZnClz gives the highest yield and stereoselectivity. It is also evident that although BFa-etherate is the best Lewis acid for the allylation reaction,' it proves to be the least effective catalyst for the cycloaddition process. We also surveyed a range of solvents and temperatures to find the best conditions for the [3 2]-reaction, using 4-nitrobenzaldehyde as substrate and 15 mol % ZnClz as catalyst. The best yields and stereoselectivities for the formation of l l f are obtained when the annulation is done in CHzC12 at room temperature (Table 2). Applying this protocol t o other carbonyl substrates, we determined that for reactions of aldehydes the best results are consistently obtained using 15 mol % ZnCl2 in CHzClz a t room temperature (Table 3). While the diastereoselectivityz2of these [3 21-reactions appears to be slightly better at lower temperature, the yields of furans are noticeably lower. For ketones, however, ZnClp is completely ineffective at catalyzing the [3 2]-cycloaddition, and Tic14 appears to be the preferred catalyst. In a few cases, the cycloaddition was found to take place in the absence of Lewis acid, but these reactions are restricted to highly activated aromatic systems (e.g., Ar = 3-NOzPh or 4-NOzPh). Operation-

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hetero-Diels-Alder reaction18J9of 1,3-dieneshas found widespread popularity for the synthesis of six-membered ring heterocycles (eq 2).20 With the goal of developing 21-approach to furans and related a general [3 heterocycles, we hoped to demonstrate the capability of Lewis acids to catalyze the allylation-cyclization procedure described above in a single operation.21

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(17)(a) Panek, J. S.; Yang, M. J. Am. Chem. SOC.1991, 113,9868. (b) Danheiser, R. L.; Stoner, R. L.;Koyama, H.; Yamashita, D. S.; Klade, C. A. J . Am. Chem. SOC.1989,111,4407.(c) van der Heide, T. A. J.; van der Baan, J. L.; de Kimpe, V.; Bickelhaupt, F.; Klumpp, G. W. Tetrahedron Lett. 1993,34, 3309. (d) van der Louw, J.; van der Baan, J. L.; Stichter, H.; Out, G . J. J.; Bickelhaupt, F.; Klumpp, G . W. Tetrahedron Lett. 1988,29,3579.(e) Trost, B. M. Angew. Chem., Int. Ed. Engl. 1986,25,1. (18)(a) Danishefsky, S. J.; Pearson, W. H.; Harvey, D. F.; Maring, C. J.; Springer, J. P. J. Am. Chem. Soc. 1985, 107, 1256. (b) Danishefsky, S.;Bednarski, M. Tetrahedron Lett. 1985,26,2507.( c ) Danishefsky, S. J.; Kenvin, J. F.; Kobayashi, S. J. Am. Chem. SOC. 1984,104,358.(d) Danishefsky, S.J.; Larson, E. R.; Askin, D. J.Am. (e) Barluenga, J.;Aznar, F.; Cabal, M. P.; Chem. Soc. 1982,104,6457. Valdes, C. Tetrahedron Lett. 1989,30,5923. (19)Kenvin, J. F.;Danishefsky, S. Tetrahedron Lett. 1982,23,3739. (20)Hetero Diels-Alder Methodologies in Organic Synthesis; Boger, D. L.,Weinreb, S. M., Eds.; Academic Press: New York, 1987;Vol. 47,Chapter 4. (21)Jiang, S.;Turos, E. Tetrahedron Lett. 1994,35,7889.

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Organometallics, Vol. 14,No. 10, 1995 4713

Allyl(cyclopentadienyl)iron(II) Dicarbonyls

Scheme 3

furan esters

Table 1. Survey of L e w i s Acid Catalysts for the [S + 21-Reaction of 1 With 4-Nitrobenzaldehyde (16 mol % in CHPC~P at 22 "C) Lewis acid

time, h

% isolated yield," ratiob

14 14 15 14 12

71, 3.1:l 61, 1.6:l 58, 1.8:l 55, 2.0:l 45, 1.51 33,1.9:1 29, 1.6:l 18, 1.9:l

15 27 28

crotyliron complex 12,2only two diastereomeric pyrrolidine esters 13 are isolated (stereochemistry not assigned).25 Intramolecular [S 21-Cycloadditions. The intramolecular addition of an allylmetal to a carbonyl center is a well-precedented method for constructing 1,2vinylcycloalkanols.26 Generally,the reaction takes place under Lewis acid conditions and provides the cycloadduct in high yield. We envisioned that application of our [3 21-cycloaddition methodology to intramolecular systems would provide a conceptually attractive approach to the synthesis of fused furan rings 16 shown as follows:

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a Isolated yields of furan esters after silica gel flash chromatography. The trans:cis ratios were determined by integration of nonoverlapping signals in the lH NMR spectrum of the mixture.

M+

ally, this catalytic Lewis acid method not only offers a more convenient procedure for effecting the [3 21-annulation, since the intermediate n-complex does not have to be isolated, but, more importantly, avoids the necessity of having to use an external base to effect the final ring closure of the n-complex. This latter feature is particularly beneficial, since the efficiency of the cyclization step is highly dependent on the purity of the intermediate n-complex formed in the initial allylation reaction. Considering that this catalytic Lewis acid procedure utilizes the carbonyl compound as the limiting reagent, the relative yields of cycloadducts are considerably improved compared to those obtained from the stepwise method employing BF3-etherate.3 Lewis Acid-Catalyzed [3 21-Reactions of Imines. This Lewis acid-catalyzedcycloaddition procedure can also be applied t o N-tosylimines for the preparation of pyrrolidine derivatives 13.23124Initial experiments

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1 ) 15mol%ZnClz C H & , rt

Me0 O

VR :

r

13a R-H, Ar=Ph (55%, 2.5:l) b R=H,Ar=3-NOzPh(42%, 2.51) C R-CHs, AkPh (28%, 2.5:l)

using 1 and the N-tosylimine of benzaldehyde (Ar= Ph) carried out in Et20 gave only low yields of the cycloadduct, which we attribute to the low solubility and reactivity of the imine-Lewis acid complex in this solvent. However, these cycloadditions take place smoothly in CHzClz solution at room temperature using 15 mol % ZnClz. Curiously, for the cycloaddition of

J '

dlylic

-..------------* deprotonation M

[3+21*

0-

A

k

14

15 M

b R

16

The salient features of the approach are the ready availability of allylmetal complex 15 by allylic deprotonationz7of cationic n-complex 14, followed by the [3 21-furan annulation. To demonstrate the feasibility of this tandem cycloaddition approach, n-complex 18 was prepared by metalationZ8of the epoxide precursor 1729(Scheme 4). Thus, reaction of epoxyketone 1730with sodium (cyclopentadienylliron dicarbonyl in THF a t 0 "C, followed by acidification with 48%fluoboric acid-acetic anhydride

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(22) Semi-emperical (Spartan AM1) calculations indicate that the trans isomer of l l a is approximately 0.3 kcal/mol more stable than the cis compound, based on their calculated heats of formation. Nuclear Overhauser enhancement (NOE) NMR studies on l l a reveal that the major and minor products are the trans and cis stereoisomers, respectively, which show the 'H NMR and NOE data indicated in Chart 1. For the remaining mixtures of stereoisomers l l b - e , the major product in each case was likewise assigned to be the trans adduct on the basis of the fact that proton Hd at the carboxyl-substituted center of the ring for each of the major (trans) isomers is shifted downfield compared to the minor (cis) isomers. Thus,these cycloadducts appear to be formed as thermodynamic mixtures under these catalytic Lewis acid conditions. Additional studies are underway to determine at what stage equilibration may be taking place and how the stereochemical selectivities might be better controlled. (23) For examples of [3 21-cycloadditionreactions of imines, see: (a) Panek, J. S.; Jain, N. F. J.Org. Chem. 1994,59,2674.(b) Trost, B. M.; Marrs, C . M. J. Am. Chem. SOC.1999,115, 6636. (c) Trost, B. M.; Bonk, P. J. J. Am. Chem. SOC.1986,107, 1778. (d) References 13c,d. (24) Pyrrolidines have also been prepared by BF3-etherate-catalyzed addition of allyltrimethylsilane to a-amino aldehyde derivatives (Kiyooka, S.4.; Shiomi, Y.; Kira, H.; Kaneko, Y.; Tanimori, S. J. Org. Chem. 1994, 59, 1958) and allyltrimethylsilane addition to an N acyliminium-type species (Stahl, A.; Steckhan, E.; Nieger, M. Tetruhedron Lett. 1994, 35, 7371).

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4714 Organometallics, Vol. 14, No. 10, 1995

Jiang et al.

Table 2. Effect of Solvent and Temperature on the ZnClz-Catalyzed [3 21-Reaction of 1 with 4-Nitrobenzaldehyde

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solvent

temp, "C

time, h

% isolated yield: ratiob

CHzClz

22 -20 -78 22 -20 22 -20 22 -20 22 -20

14 24 37

71,3.1:l 41,3.51 25,3.4:l 40,2.5:1 2,1.9:l 34,1.8:l 21,2.3:l 29,2.0:l 8,1.9:l 22,2.0:l 3, 1.5:l

THF hexane EtzO benzene toluene

14 22 14 21 13 20 14 23

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a Isolated yields of furan esters after flash chromatography on silica gel. The transcis ratios were determined by integration of nonoverlapping signals in the lH NMR spectrum of the mixture.

and dilution with EtzO, provided It-complex 18 as a yellow precipitate in 70% yield.31 Treatment of n-complex 18 with a slight molar excess of Et3N a t 0 "C in CH2C12 gives allyliron complex 19 in 73% yield, which upon isolation by evaporation was treated with 15 mol % ZnCl2 in CH2Ch at -20 "C t o effect the cyclization. After 24 h, the crude mixture containing the iron furan was then added to a methanolic solution of ceric ammonium nitrate (5 equiv) a t -78 "C under an atmosphere of CO. After evaporation and flash chromatography of the crude material, tricyclic furan esters 20 were obtained as a 2.3:l mixture of epimers in 42% combined yield (30% combined overall yield from n a d duct 18).32Efforts are now underway to utilize this tandem cyclization strategy for the synthesis of multi(25)A similar outcome was observed for the cyclization of zwitterionic n-adducts i prepared from complex 16 using the BFS-etherate procedure.

I

W H , 1 am CO

il(2 i k " ,

cyclic fused ring systems having different ring sizes and heteronuclei within the skeleton. To summarize our results, we have found that primary alkoxides add regiospecifically to the internal alkene center of iron-olefin It-complexes 2 to afford 1,3,5triol derivatives. By carrying out these additions in an aprotic solvent, the zwitterionic salts can be cyclized to a furan adduct using a mild base to cleave the O-BF3 linkage. The [3 21-cycloaddition of allyliron complexes with carbonyl compounds and imines may be carried out in the presence of an appropriate Lewis acid catalyst. Intramolecular allyliron-ketone cycloadditions can be effected to construct multicyclic furan frameworks in a single step. Ongoing investigations in our laboratory are focusing on applications of this 13 21methodology to the synthesis of selected heterocyclic structures common t o those in naturally occurring compounds.

14%)

Thus, treatment of the diastereomeric mixture of n-complexes with potassium tert-butoxide in CHZClz, followed by esterification with methanolic ceric ammonium nitrate, gave only two cycloadducts ii in 14% combined yield (stereochemistry undetermined). We believe that two of the diastereomeric n-complexes can cyclize without difficulty, while the other two isomeric forms may have severe steric interactions within the transition state that prevent cyclization. (26)(a) Denmark, S.E.; Weber, E. J. Helu. Chim. Acta 1983,66, 1655.(b) Denmark, S. E.; Weber, E. J. J . Am. Chem. SOC.1984,106, 7970.(c) Denmark, S.E.; Henke, B. R.; Weber, E. J. Am. Chem. SOC. 1987,109,2512.(d) Lee, T. V.; Roden, F. S.;Yeoh, H. T.-L.Tetrahedron (e) Lee, T.V.; Roden, F. S. Tetrahedron Lett. 1990, Lett. 1990,31,2063. 31,2067.(0 Nishitani, K.; Yamakawa, K. Tetrahedron Lett. 1991,32, 387.(g) Marshall, J. A.; DeHoff, B. S.; Crooks, S. L. Tetrahedron Lett. 1987,28,527. (h) Marshall, J.A.; Gung, W. Y. Tetrahedron Lett. 1988, 29,1657.(i) Marshall, J.A.; Markwalder, J. A.Tetrahedron Lett. 1988, 29, 4811.cj) Marshall, J. A,; Gung, W. Y. Tetrahedron Lett. 1989,30, 2183.(k) Marshall, J.A.; Welmaker, G. S.; Gung, B. W. J . Am. Chem. SOC.1991,113,647.(1) Asao, K.;Iio, H.; Tokoroyama, T. Tetrahedron Lett. 1989,30, 6397.(m) Gevorgyan, V.;Kadota, I.; Yamamoto, Y. Tetrahedron Lett. 1993,34, 1313. (27)Cutler, A.; Ehntholt, D.; Lennon, P.; Nicholas, K.; Marten, D. F.; Madhavarao, M.; Raghu, S.; Rosan, A.; Rosenblum, M. J.Am. Chem. SOC. 1976,97,3149. (28)Giering, W. P.; Rosenblum, M.; Tancrede, J. J . Am. Chem. SOC. 1972,94,7170. (29)Alternatively, n-complex 18 can be obtained by refluxing a solution of Fe(C0)ZCp-isobutylene fluoborate with the olefin in CHzClz. (30)Epoxy ketone 17 was prepared from cycloheptanone in three steps: (1)cyclohexylamine,PhH, pTsOH, reflux (90%);(2)LDA, THF, -78 "C, and then HMPA and 5-bromopent-1-ene(83%);(3)mCPBA, CH2C12 (83%).

+

Experimental Section All reactions were performed under an argon atmosphere using glassware a n d syringes that were predried overnight i n an oven at 120 "C and assembled while still hot. The aldehydes and ketones were purchased (Aldrich Chemical Co.) and used without further purification. N-Tosylimines were prepared by refluxing the aldehyde with N-toluenesulfonamide i n benzene or toluene in the presence of a catalytic amount of p-toluenesulfonic acid. Benzyl alcohol and allyl alcohol were vacuum distilled immediately prior to use. Potassium tertbutoxide was sublimed under vacuum. The allylic (cyclopentadienyl)iron(II) dicarbonyl complexes 1and 12 were prepared as described2 by Green a n d Nagy, except that the final purification step (alumina column chromatography) was omitted. THF and Et20 were distilled immediately prior t o use from Nahenzophenone under argon. CH2C12, benzene, toluene, and hexane were freshly distilled from CaH2 under Nz, a n d CH30H was distilled from M g under argon. Flash chromatography was performed using J. T. Baker flash chromatography silica gel (40pm). TLC was carried o u t using EM Reagents plates with fluorescence indicator (SiO2-60, F-254). 'H NMR spectra were recorded using a Varian 400 NMR instrument at 400 MHz in CDC13. 13C NMR spectra were recorded using a Varian Gemini 300 NMR spectrometer at 75 MHz i n CDCl3. IR spectra were measured on a Perkin-Elmer 1310 spectrophotometer as a t h i n film on NaCl plates. Mass spectra were run using chemical ionization (CI) or fast-atom bombardment (FAB) ionization. Combustion analyses were performed by Atlantic Microlabs (Atlanta, GA).

Representative Procedure for the Preparation of Diols 8a-d. To a solution of 3-nitrobenzaldehyde (151 mg, 1.0 mmol) and BFs-etherate (0.250mL, 2 mmol) i n anhydrous Et20 (10mL) at rt (rt = room temperature) is added a freshlyprepared solution of 1 (5 mL, 0.5M, 2.5 mmol) i n anhydrous EtzO. The mixture is stirred at rt for 3 h and evaporated in uucuo. The residue is dissolved i n CH30H (10 mL), and anhydrous KzC03 (207 mg, 1.5 mmol) is added at 0 "C. The (31)Iron-olefin n-complex 18 gave the following spectral data: the 'H NMR spectrum shows a singlet at 5.90ppm for the Cp protons and signals at 5.28,4.05, and 3.63 ppm for the vinyl protons; the I3C NMR spectrum gives resonances at d 217.1 (ketone), 210.2and 208.8(C-01, and 89.5(Cp);twin metal C=O stretching bands are observed at 2070 and 2030 cm-l and a C-0 ketone stretch appears at 1695 cm-l in the infrared spectrum; the FAB mass spectrum shows signals of M-BFd (357.0)and Fp+ (177.0). (32)We have assigned these products to be epimeric esters each having the cis-cis fused ring skeleton, which molecular modeling calculations (Spartan AM1 semi-emperical, gas phase) predict is favored over the cis-trans [5.5.7.l-fused system by approximately 1.5 kcaymol. Of the two epimeric structures shown in Chart 2,the major isomer is about 2 kcal/mol more stable according to the calculated gas phase heats of formation. 'H-decoupling NMR and 'H NOE difference data that support these assignments are also shown in Chart 2.

Organometallics, Vol. 14, No. 10,1995 4715

Allyl(cyclopentadienyl)iron(II) Dicarbonyls Table 3. [3

+ 21-CycloadditionReactions of Iron Complex 1 and Carbonyl Compounds

Carhnvl Comwund

Product

Roactlon condlflono

76 vldb. roblob

36%(2.1:l) 40% ( 1 . 1 :1) B% (1.8:l)

ZnCh(l5 mol%), Cl+Clz, RT

62% (2.7:l)

Lewis add,CHzCh, RT

45%(1.9:l)

0

cH303 0%

37%

ZnClz (100 mol%), CHfi12, RT

0%

TCI4 (200mol%),CHfi12, -78%

15% (1.O:l)

ZnCh (15 mol%), CH2CIz,RT

71X(3.1:1)

ZnCh (100 mol%), CH&Iz,RT

%(1,l:l)

Lewis acid,CH2C12, RT

60% (1.9:l)

ZnCh (15 mol%), CHzCIz,RT

31% (2.0:l)

ZnCh (100 mol%), CHZCIz, RT

28%(1.2:l)

Ix)

0

c

H

3

0

9

c"300w ZnClz (100 mol%), CH&12. RT

16%'

TICI, (200mol%), CH&Iz, -78%

15%'

'kdated yields after flash chromatographyon silica gel. Ratios determined by integrationof nonoverlapping signals in the 'H NMR spectrum. Ratios not determined due to overlapping signals in the 'H NMR spedrum.

mixture is stirred vigorously at 0 "C for 1h. The progress of the reaction is followed by periodically removing a small aliquot and observing the disappearance of the twin CO infrared stretching bands at 2075 and 2035 cm-' for the n-complex and the appearance of new signals at 2000 and 1945 cm-l for the u-complex. The reaction typically reaches completion within 1 h, at which time the reaction mixture is transferred dropwise over a 30 min period t o a solution of ceric ammonium nitrate (4.1g, 7.5 mmol) in CH3OH (20 mL) at -78 "C under a CO atmosphere. After the solution is stirred at -78 "C for an additional 30 min, the solvent is warmed to rt and allowed to stir for an additional 30 min and then evaporated in uucuo. The residue is dissolved in H20 (15 mL) and extracted with Et20 (5 x 15 mL). The combined ethereal layers are washed with brine (15 mL) and saturated NaHC03, dried over anhydrous MgS04, and evaporated. -The crude product is dissolved in THF (10 mL) and treated with LiBH4 (109 mg, 5 mmol) at rt for 12 h. The reaction is quenched by the addition of HzO (10 mL), and the mixture is adjusted to pH 4 using 1N HC1 and extracted with CHzCl2 (5 x 20 mL). The organic layer is washed with brine (15 mL), dried over

anhydrous MgS04, and evaporated. Flash chromatography (acetone/CH&lz) of the mixture gives 136 mg (53%, 1.2:l mixture of diastereomers) of diol 8b. lH NMR (400 MHz, CDC13): isomer 1 , 6 8.27 ( 8 , lH), 8.13(d, J = 7.8 Hz, lH), 7.71 (d, J = 7.8 Hz, lH), 7.52 (t,J = 7.8 Hz, lH), 5.14 (d, J = 7.8 Hz, lH), 3.81 (m, 2H), 3.71 (m, 1H and OH), 3.45 (s, 3H), 2.092.00 (m, lH), 2.00-1.83 (m, 3H and OH); isomer 2, 6 8.25 (s, lH), 8.13 (d, J = 8.8 Hz, lH), 7.73 (d, J = 7.8 Hz, lH), 7.52 (dd, J = 7.8, 8.8 Hz, lH), 5.01 (dd, J = 2.0, 9.8 Hz, lH), 4.10 (s, OH), 3.81 (m, 2H), 3.75 (m, lH), 3.47 (s, 3H), 2.05-1.80 (m, 4H), 1.77 (br s, OH). 13CNMR (75 MHz, CDC13) (mixture of diastereomers): 6 149.0, 149.0, 147.8, 147.5, 132.5, 132.3, 129.9, 122.9, 122.7, 121.3, 121.1, 79.9, 72.9, 70.8, 59.9, 59.5, 57.4, 56.7, 43.4, 42.2, 35.3, 35.4. IR (neat film) (mixture of diastereomers): 3420 (br),3064,2944,1530,1350,1263,1067, 728, 698 cm-l. MS (CI, isobutane) (mixture of diastereomers): mlz 238 (M + 1 - HzO, 33), 207 (12), 206 (loo), 194 (26), 190 (111, 188 (23), 169 (111, 162 (121, 152 (281, 150 (611, 149 (17), 136 (11). HRMS (CI, isobutane) (mixture of diastereomers): calculated for Ci~Hi&J04(M + l - HzO), 238.1079; found 238.1053.

Jiang et al.

4716 Organometallics, Vol. 14,No.10, 1995

Chart 1

major diaatereomer

minor diastereomr

Selected 'H NMR spectral Data Major isomer Minor isomer 6 4.87 (dd, J-966.0 HZ) 6 5.02 (t, J=7.4 Hz) 6 2.17 (m) 6 2.05 (m) 8 2.59 (m) 6 2.64 (m) 6 3.29 (m) 6 3.25 (m) 6 4.29 (dd. J=6.9, 6.0 Hz) 6 4.34 (t, J 4 . 2 Hz) 6 4.11 (t, J 4 . 8 M ) 6 4.05 (1, J=7.4 Hz)

Proton

Diol 8a: 55% yield (115 mg, 0.55 mmol, 1.1:l). 'H NMR (400 MHz, CDC13): isomer 1,6 7.39-7.27 (m, 5H), 4.98 (dd, J = 3.6, 6.8 Hz, lH), 3.85-3.71 (m, 2H), 3.68 (m, lH), 3.43 ( s , 3H), 3.08 (br s, OH), 2.02-1.90 (m, 2H), 1.87 (m, 2H), 1.60 (br s, OH); isomer 2, 6 7.39-7.27 (m, 5H), 4.87 (dd, J = 3.6, 9.2 Hz, lH), 3.81 (m, lH), 3.76-3.67 (m, 2H), 3.43 (s, 3H), 2.121.74 (m, 4H and 20H). 13C NMR (75 MHz, CDC13) (mixture of diastereomers): 6 145.4, 145.2, 129.0, 128.1, 127.9, 126.3, 126.1, 80.0, 78.2, 73.5, 71.7, 60.2, 60.0, 57.3, 56.7, 43.3, 42.5, 35.8, 35.5. IR (neat film) (mixture of diastereomers): 3380 (br), 2950,1450,1370,1060,750,695cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 193 (M + 1 - HzO, 181, 178 (20), 177 (9), 163 (14), 162 (181, 161 (1001, 160 (521, 159 (20), 149 (57), 147 (13), 145 (451, 143 (191, 133 (12), 131 (241, 129 (151, 117 (471, 115 (18), 107 (431, 105 (471, 104 (35). HRMS (CI, isobutane) (mixture of diastereomers): calcd for C1zH1702 (M 1 - HzO), 193.1229; found, 193.1236. Diol 8c: 47% yield (120 mg, 0.47 mmol, 1.1:l).'H NMR (400 MHz, CDC13): isomer 1, 6 8.21 (d, J = 8.8 Hz, 2H), 7.55 (d, J = 8.8 Hz, 2H), 5.01 (dd, J = 2.0, 9.6 Hz,lH), 4.11 (9, OH), 3.85-3.69 (m, 3H), 3.47 (s, 3H), 2.01-1.80 (m, 4H), 1.77 (s, OH); isomer 2, 6 8.21 (d, J = 8.8 Hz, 2H), 7.54 (d, J = 8.8 Hz, 2H), 5.13 (d, J = 8.8 Hz, lH), 3.79 (m, 2H), 3.72 (s, OH), 3.68 (m, lH), 3.43 (s, 3H), 2.07-1.82 (m, 4H and OH). NMR (75 MHz, CDC13) (mixture of diastereomers): 6 153.0, 152.7, 147.8, 147.8, 127.0, 126.9, 124.2, 80.0, 77.9, 73.0, 71.0, 59.9, 59.6,57.3,56.7,43.4,42.2,35.4.IR (neat film) (mixture of diastereomers): 3380 (br), 2940, 1515,1344,1067,851cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 256 (M 1,2),238 (M 1- HzO, 331,208 (431,207 (25),206 (100),194 (22), 176 (26), 152 (161, 150 (361, 122 (171, 120 (111,115 (121, 106 (16). HRMS (CI, isobutane) (mixture of diastereomers): calcd for C12H&O4 (M 1 - HzO), 238.1079; found, 238.1072. Diol 8d: 30% yield (66 mg, 0.30 mmol), 1.1:l). 'H NMR (400 MHz, CDC13) (mixture of diastereomers): 6 3.9-3.62 (m, 4H), 3.42 (s) and 3.41 (s) (total 3H), 2.55 (br, OH), 2.15 (br, OH), 1.95-1.20 (m, 14H), 0.88 (t,J = 6.0 Hz, 3H). 13C NMR (75 MHz, CDC13)(mixture of diastereomers): 6 80.3,78.3,71.1, 69.2, 60.2, 59.9, 57.2, 56.7, 40.9, 40.1, 38.2, 38.2, 36.0, 35.7, 32.0, 29.5, 25.8, 25.6, 22.8, 14.2. IR (neat film) (mixture of diastereomers): 3360 (br), 2940,1865,1460,1374,1185,1075 cm-1. MS (CI, isobutane) (mixture of diastereomers): mlz 219 (M 1, 40), 202 (6), 201 (47), 199 (61, 175 (91, 171 (141, 170 (12), 169 (loo), 158 (lo), 157 (881, 151 (181, 149 (141, 139 (5), 131 (ll),115 (ll), 109 (6). HRMS (CI, isobutane) (mixture of diastereomers): calcd for C12H2703 (M + 11, 219.1960; found, 219.1908.

+

+

+

+

+

Representative Procedure for the Preparation of Diols 8e-f. To a solution of 4-nitrobenzaldehyde (151 mg, 1.0 mmol) and BF3-etherate (0.250 mL, 2 mmol) in anhydrous Et20 (10 mL) at rt is added a 0.5 M solution of 1 (5 mL, 2.5 mmol) in anhydrous EtzO. The mixture is stirred at rt for 3 h and evaporated in vacuo. The residue is dissolved in benzyl

alcohol (20 mL) (or allyl alcohol), and a mixture of NaH (80 mg, 60% in mineral oil, 2 mmol) in benzyl alcohol (5 mL) (or allyl alcohol) is added dropwise to the solution at 0 "C over 10 min. After being stirred vigorously at 0 "C for 1h, the mixture is transferred dropwise over a 30 min period to a solution of ceric ammonium nitrate (4.1 g, 7.5 mmol) in CH30H (20 mL) at -78 "C under a CO atmosphere. The mixture is stirred at -78 "C for 30 min and at rt for a n additional 30 min. The solvent is concentrated in uucuo to half-volume, mixed with water (15 mL), and extracted with Et20 (5 x 15 mL). The combined ethereal layers are washed with brine (15 mL) and saturated NaHC03 (2 x 10 mL), dried over anhydrous MgS04, and concentrated t o remove the ether. The remaining liquid is diluted with THF (10 mL) and treated with LiBH4 (109 mg, 5 mmol) at rt for 12 h. The reaction is quenched by the addition of HzO (15 mL), and the mixture is adjusted to pH 4 using 1 N HC1 and extracted with CHzClz (5 x 15 mL). The organic layer is washed with brine (15 mL), dried over anhydrous MgS04,and evaporated in vacuo (maintaining the pot temperature below 85 "C). Purification of the crude product by successive flash chromatography (acetone/CHzClz) gives 73 mg (22%, 1.3:l mixture of diastereomers) of diol 8e. lH NMR (400 MHz, CDC13) (mixture of diastereomers): 6 8.18 (overlapping d, J = 8.8 Hz, 2H), 7.50 (overlapping d, J = 8.8 Hz, 2H), 7.37 (m, 5H), 5.09 (dd, J = 2.9, 5.8 Hz) and 4.98 (dd, J = 2.0, 8.8 Hz) (total lH), 4.74-4.53 (m, 2H), 4.06-3.90 (m, 1H), 3.85-3.70 (m, 2H), 4.02 (s) and 3.40 (d, J = 3.0 Hz) (total lH, OH), 2.06-1.84 (m, 4H), 1.17 (m, OH). I3C NMR(75 MHz, CDC13) (mixture of diastereomers): 6 153.0, 152.7, 147.8, 147.7, 138.4, 138.1, 129.2, 128.7, 128.6, 127.1, 126.9, 124.2, 75.3, 72.8, 72.0, 71.5, 70.8, 59.8, 59.5, 43.7, 42.8, 36.1, 36.0. IR (neat film) (mixture of diastereomers): 3400 (br), 2958, 2886, 1661, 1517, 1345, 1263,1060, 850, 730, 692 cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 314 (M 1 HzO, lo), 296 (25), 284 (39), 268 (lo), 224 (33), 223 (lo), 222 (23), 210 (19), 208 (17), 207 (12), 206 (511, 204 (271, 196 (201, 193 (lo), 192 (25), 190 (291, 189 (181, 188 (191, 184 (111, 178 (471, 177 (16), 176 (501, 176 (26), 175 (151, 174 (58), 165 (14, 160 (47), 159 (201, 158 (181, 152 (17), 150 (44), 146 (291, 145 (14), 144 (lo), 138 (111, 132 (111,129 (121, 122 (211, 120 (201, 108 (15), 108 (17), 107 (loo), 106 (27). HRMS (CI, isobutane) (mixture of diastereomers): calcd for CreHzoNOc (M + 1 HzO), 314.1392; found, 314.1375. Diol 8E 20% yield (57 mg, 0.20 mmol, 1.1:l).'H NMR (400 MHz, CDC13)(mixture of diastereomers): 6 8.21 (overlapping d, J = 8.8 Hz, 2H), 7.55 (d, J = 8.0 Hz, 2H), 5.95 (m, lH), 5.36-5.23 (m, 2H), 5.15-5.01 (m, lH), 4.23-3.92 (m, 3H), 3.90-3.70 (m, 2H), 3.63 ( 8 , OH), 2.04-1.84 (m, 4H), 1.79 (s) and 1.74 (9) (total l H , OH). 13C NMR (75 MHz, CDC13) (mixture of diastereomers): 6 152.9, 152.6, 147.9, 147.8,134.8, 134.6, 127.0, 126.9, 124.2, 118.5, 118.2, 78.1, 75.9, 73.2, 70.9, 70.9, 703, 60.0, 59.6, 43.7, 42.4, 36.0, 35.9. IR (neat film) (mixture of diastereomers): 3400 (br), 2930,2880, 1602, 1516, 1420,1345,1070,920,852,723,694cm-l. MS (CI, isobutane) (mixture of diastereomers): mlz 282 (M 1,2), 264 (M 1HzO, 131,234 (81, 224 (51,212 (42), 208 (17),207 (51,206 (28), 194 (11). HRMS (CI, isobutane) (mixture of diastereomers): calcd for C14HleN04 (M + 1- HzO), 264.1236; found, 264.1368.

+

+

+

RepresentativeProcedure for the Silylationand Acetylation of Diols 8. A solution of diol 8b (128 mg, 0.5 mmol) in CHzClz is treated with tBuMe2SiC1 (226 mg, 1.5 mmol), pyridine (240 pL, 3.0 mmol), and DMAP (6 mg, 0.05 mmol) and is allowed to stir for 24 h and then evaporated in vacuo. The crude product is dissolved in a mixture of pyridine (10 mL) and AczO (2.4 mL, 25 mmol), stirred for 12 h, and evaporated in vacuo. The residue is taken up in Et20 (30 mL) and washed with 10% CuS04 (2 x 5 mL) and brine (10 mL), dried over MgS04, and evaporated. Flash chromatography (acetone/CHzClz) of the impure oil gives 170 mg of triol derivative 9b (83% from the diol, 1.3:l mixture of diastereomers). 'H NMR (400 MHz, CDC13) (mixture of diastereomers): 6 8.23 (9) and 8.21 (s) (total lH), 8.15 (overlapping d, J = 7.8 Hz, lH), 7.67 (overlapping d, J = 6.8 Hz, lH),

Organometallics, Vol. 14,No. 10, 1995 4717

Allyl(cyclopentadienyl)iron(II) Dicarbonyls

Scheme 4

CH& 0°C (73%)

then HBFJAeO

18

17

L --

(42%)

19

R 20 (2.31 mixture) 30% overall yieM from 18

Chart 2

ii

A mnjor disrtereomer Proton

minor diastereomer

Selected 'H NMR Spectral Data Major Isomer 8 3.13 (dt,J=9.8,7.8 Hz) 8 2.74 (m) 62.41 (dt, J-10.7, 7.8 HZ) S 2.47 (m) 6 4.08 (dd,J=9.8,8.8 Hz) S 3.87 (t, &8.8 Hz) 84.09 (dd,J-8.8,7.8 Hz) 83.98 (dd, J=7.8,8.8 HZ)

7.51 (m, lH), 6.01 (dd, J = 2.9, 10.6 Hz) and 5.96 (t, J = 7.3 Hz) (total lH), 3.73'358 (m, 2H), 3.47 (m) and 3.19 (m) (total lH), 3.34 (s) and 3.26 (s) (total 3H), 2.22 (m)and 1.93 (m) (total lH), 2.11 (s) and 2.08 (s) (total 3H), 1.79 (m, 2H), 1.64 (m, lH), 0.88 (s) and 0.81 (s) (total 9H), 0.05 to -0.02 (m, 6H). I3C NMR (75 MHz, CDC13) (mixture of diastereomers): 6 170.7, 170.6, 149.1, 144.2, 143.5, 133.6, 133.2, 130.1, 130.0, 123.4, 123.3, 122.1, 121.6,75.0, 74.8,73.1,72.3,59.5,59.4,57.6,56.2, 42.4, 40.7, 37.1, 36.4, 26.0, 26.0, 21.2, 21.2, 18.3, 18.3, -5.3, -5.4. IR (neat film) (mixture of diastereomers): 2940, 2864, 1745,1633,1532,1464,1349,1230,1088,1019,832,803,773 cm-l. MS (CI, isobutane) (mixture of diastereomers): mlz 412 (M 1, l),322 (19), 291 (14),290 (651,264 (lo), 232 (17), 203 (29), 190 (16), 160 (18),159 (lo), 158 (461, 146 (151, 145 (201, 133 (22), 132 (loo), 120 (13), 119 (11). HRMS (CI, isobutane) (mixture of diastereomers): calcd for CzoH3rNO&i (M + l), 412.2155; found, 412.2163. Anal. Calcd for CzoHssNOsSi: c, 58.37; H, 8.08; N, 3.40. Found: C, 58.50; H, 8.16; N, 3.41. Triol Derivative 9a: 65% yield (120 mg, 0.33 mmol). 'H NMR (400 MHz, CDC13) (mixture of diastereomers): 6 7.367.32 (m, 5H), 5.94 (dd, J = 4.0, 10.8 Hz) and 5.88 (t, J = 7.4 Hz) (total lH), 3.74-3.58 (m, 2H), 3.42 (m) and 3.20 (m) (total lH), 3.33 (s) and 3.26 (s) (total 3H), 2.20 (m) and 1.92-1.60 (m) (total 4H), 2.07 (s) and 2.04 (s) (total 3H), 0.89 (s) and 0.84 (s) (total 9H), 0.05 t o -0.01 (m, 6H). 13C NMR (75 MHz, CDC13) (mixture of diastereomers): 6 170.9, 170.8, 141.8, 141.1, 129.1, 128.5, 128.4, 127.4, 126.9, 75.2, 75.1, 74.2, 73.3, 59.6, 59.5, 57.6, 56.4, 42.2, 40.9, 37.4, 36.9, 26.1, 21.5, 21.4, 18.4, 18.4, -5.3, -5.3. IR (neat film) (mixture of diastereomers): 2935,2864, 1740,1633,1460,1365,1234, 1085,1014, 831, 770 cm-'. MS (CI, isobutane) (mixture of diastereo51, 276 (211, 275 (911, mers): mlz 307 (M 1 - CH~COZH, 203 (41), 191 (24), 149 (26), 145 (161, 143 (171, 118 (ll),117 (loo), 115 (10). HRMS (CI, isobutane) (mixture of dia-

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+

stereomers): calcd for C18H3102Si (M + 1 - CH~COZH), 307.2093; found, 307.2062. Triol Derivative 9c: 77% yield (158 mg, 0.38 mmol). 'H NMR (400 MHz, CDC13) (mixture of diastereomers): 6 8.20 (overlapping d, J = 8.8 Hz, 2H), 7.50 (overlapping d, J = 8.8 Hz, 2H), 5.99 (dd, J = 2.8, 10.6 Hz) and 5.94 (t, J = 6.8 Hz) (total lH), 3.74-3.58 (m, 2H), 3.47 (m) and 3.19 (m) (total lH), 3.34 (s) and 3.25 (s) (total 3H), 2.21 (m) and 1.91 (m) (total 1H), 2.11 (s) and 2.07 (s) (total 3H), 1.86-1.70 (m, 2H), 1.63 (m, lH), 0.88 (s) and 0.82 (s) (total 9H), 0.05 t o -0.02 (m, 6H). l3C NMR (75 MHz, CDC13)(mixture of diastereomers): 6 170.7, 170.6, 149.3, 148.6, 148.2, 148.1, 128.1, 127.5, 124.4, 124.3, 74.9, 74.8, 73.1, 72.4, 59.5, 59.4, 57.6, 56.2, 42.3, 40.6, 37.0, 36.4, 26.0, 26.0, 21.2, 21.1, 18.3, 18.3, -5.3, -5.4. IR (neat film) (mixture of diastereomers): 2935,2864,1744,1607,1524, 1463, 1345, 1229, 1090, 832, 772 cm-l. MS (CI, isobutane) (mixture of diastereomers): mlz 412 (M + 1,51, 352 (161, 322 (14),320 (16), 292 (121,291 (261,290 (loo), 264 (191,204 (121, 203 (62), 188 (111, 176 (101, 160 (151, 159 (U), 158 (191, 150 (151, 146 (16), 145 (441, 133 (311, 132 (131, 119 (281, 106 (24). HRMS (CI, isobutane) (mixture of diastereomers): calcd for C2,J&aNO& (M l),412.2155; found, 412.2139. Triol Derivative 9d: 70% yield (75 mg, 0.20 mmol). lH NMR (400 MHz, CDC13) (mixture of diastereomers): 6 5.124.94 (m, lH), 3.68 (m, 2H), 3.42-3.24 (m, lH), 3.31 (s) and 3.30 (s) (total 3H), 2.04 (s) and 2.02 (s) (total 3H), 1.88-1.50 (m, 6H), 1.27 (m, 8H), 0.89 (s, 12H), -0.05 (9, 6H). 13CNMR (75 MHz, CDC13) (mixture of diastereomers): 6 171.4, 171.3, 75.6, 75.3, 72.2, 71.9, 59.7, 59.6, 57.5, 56.5, 39.8, 38.4, 37.6, 37.1, 35.2, 34.7, 31.9, 29.4, 26.1, 25.3, 22.7, 21.4, 18.4, 18.4, 14.2, -5.3, -5.3. IR (neat film) (mixture of diastereomers): 2940,2870,1740,1460,1522,1368,1240,1090,1015,833,771 cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 375 (M 1, 91), 345 (9), 344 (331, 343 (1001, 317 (20), 316 (14), 315 (701,284 (91,283 (531,257 (101,203 (191,152 (61,151 (64), 145 (12), 135 (61, 133 (71, 129 (121, 119 (g), 117 (91, 109 (91, 107 (9), 101 (5). HRMS (CI, isobutane) (mixture of diastereomers): calcd for CZ0H4304Si(M + l),375.2931; found, 375.2890. Triol Derivative 9e: 70% yield (72 mg, 0.15 mmol). lH NMR (400 MHz, CDCl3): isomer 1, 6 8.17 (d, J = 8.0 Hz, 2H), 7.45 (d, J = 8.0 Hz, 2H), 7.33 (m, 5H), 5.97 (dd, J = 2.9, 10.0 Hz, lH), 4.58 (d, J = 11.2 Hz, lH), 4.41 (d, J = 11.2 Hz, lH), 3.79-3.64 (m, 3H), 2.08 (m, lH), 2.00 (s, 3H), 1.95-1.83 (m, 2H), 1.70 (m, 1H), 0.88 (s, 9H), 0.05 (s, 6H); isomer 2, 6 8.13 (d, J = 8.8 Hz, 2H), 7.36-7.28 (m, 7H), 5.90 (t,J = 7.0 Hz, lH), 4.53 (d, J = 11.2 Hz, lH), 4.31 (d, J = 11.2 Hz, lH), 3.703.60 (m, 2H), 3.45 (m, lH), 2.27 (m, lH), 2.03 (s, 3H), 1.99 (m, 1H), 1.85 (m, lH), 1.72 (m, lH), 0.82 (s, 9H), -0.02 (s, 6H). 13CNMR (75 MHz, CDC13)(mixture of diastereomers): 6 170.6, 170.5, 149.4, 148.5, 148.2, 148.1, 139.0, 138.8, 129.0, 128.7, 128.4, 128.4, 128.3, 128.1, 127.5, 124.4, 124.3,73.1, 73.0, 72.5, 72.5, 71.8, 70.9, 59.6, 59.5, 42.5, 41.0, 37.2, 37.0, 26.1, 26.0,

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Jiang et al.

4718 Organometallics, Vol. 14, No. 10,1995 21.2, 21.1, 18.4, 18.3, -5.3, -5.4. IR (neat film) (mixture of diastereomers): 2962, 2940, 2864, 1744, 1604, 1520, 1460, 1345,1225,1090,832,770,730,690cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 488 (M + 1,31,291 ( E ) , 290 (161, 290 (621, 279 (121, 189 (481, 188 (11), 187 (221, 150 (35), 145 (21), 133 (231, 131 (12), 131 (54), 108 (141, 107 (100). HRMS (CI, isobutane) (mixture of diastereomers): calcd for C26H38N06Si (M l), 488.2468; found, 488.2454. Triol Derivative 9f 64% yield (79 mg, 0.18 mmol). IH NMR (400 MHz, CDCl3): isomer 1,d 8.19 (d, J = 8.8 Hz, 2H), 7.50 (d, J = 8.8 Hz, 2H), 5.94 (t, J = 6.8 Hz, lH), 5.87 (m, lH), 5.28-5.14 (m, 2H), 3.97 (m, lH), 3.78 (m, lH), 3.69-3.58 (m, 2H), 3.36 (m, lH), 2.23 (m, lH), 2.06 (8,3H), 1.95 (m, 1H), 1.76 (m, 1H), 1.66 (m, lH), 0.81 (s, 9H), -0.01 (d, J = 4.0 Hz, 6H); isomer 2, 6 8.20 (d, J = 8.8 Hz, 2H), 7.49 (d, J = 8.8 Hz, 2H), 5.98 (dd, J = 4.0, 10.8 Hz, lH), 5.89 (m, lH), 5.27-5.15 (m, 2H), 4.05 (m, lH), 3.90 (m, lH), 3.74-3.60 (m, 3H), 2.09 (s, 3H), 1.87-1.76 (m, 2H), 1.68-1.60 (m, 2H), 0.88 (9, 9H), 0.05 (s, 6H). 13C NMR (75 MHz, CDC13) (mixture of diastereomers): 6 170.6, 170.5, 149.3, 148.6, 148.2, 148.1, 135.6, 135.5, 128.1,127.5, 124.3, 124.3, 117.6,117.1,73.2,73.1,72.7, 72.4, 71.1, 69.9, 59.5, 59.4, 42.5, 40.9, 37.6, 37.0, 26.0, 26.0, 21.2, 21.1, 18.3, 18.3, -5.3, -5.4. IR (neat film) (mixture of diastereomers): 2960, 2940, 2864, 1744, 1605, 1523, 1463, 1367,1345,1230,1090,930,832,770cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 378 (M + 1 - CH&02H, l ) , 291 (14), 290 (511, 290 (111,229 (371, 220 (111, 190 (131, 188 (151, 187 (131, 176 (14), 173 (131, 162 (121, 160 (281, 158 (11), 150 (23), 147 (131, 146 (201, 145 (721, 145 (231, 133 (131, 132 (141, 131 (251, 129 (461,129 (151, 120 (171, 119 (161, 117 (131, 115 (16), 115 (12), 113 (lo), 108 (26), 107 (121, 106 (591, 101 (10). HRMS (CI, isobutane) (mixture of diastereomers): calcd for CZ0H32N04Si(M + 1 - CH~COZH),378.2101; found, 378.2057. Representative Procedure for [3 21-Cycloadditions

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via Cyclization-CO Insertion Reactions of Iron-Olefin mcomplexes. Preparation of Iron-Olefin mcomplexes. A freshly-prepared solution of allyl(cyclopentadienyl)iron(II) dicarbonyl(1, 14 mmol) in 50 mL of anhydrous Et20 is added t o a stirred mixture of benzaldehyde (3.78 g, 42 mmol) and BF3-etherate (1.72 mL, 14 mmol) in anhydrous Et20 (100 mL) a t 0 "C. The mixture is stirred at 0 "C for 3 h, and the yellow precipitate is collected by filtration under an argon atmosphere, washed with anhydrous Et20 (150 mL), and dried in vacuo to afford 4.21 g (80%) of iron-olefin n-complex 2a. A similar procedure gives 2b (4.89 g, 80%), 2c (4.43 g, 75%), 2d (2.17 g, 45%), and 2e (2.45 g, 50%). Cyclization-CO Insertion Reactions of Iron-Olefin mcomplexes. To a solution of iron-olefin n-complex (188 mg, 0.50 mmol) in CHzClz is added KOtBu (62 mg, 0.55 mmol) a t -20 "C, followed by the addition of acetone (1 mL). The mixture is allowed to stir at -20 "C for 12 h. After being warmed t o rt, the mixture is added dropwise over a 30 min period to a solution of ceric ammonium nitrate (1.37 g, 2.5 mmol) in methanol (10 mL) at -78 "C under a CO atmosphere. After the mixture is stirred at -78 "C for an additional 30 min, the solvent is warmed t o rt and allowed to stir for an additional 30 min and then evaporated in vacuo. The residue is triturated several times with small portions of CHzClz until the washings are colorless, and the washings are transferred t o a Si02 flash column and eluted with CHzClz and then 2% acetone in CH2C12. After further purification by a second flash column, 46 mg of tetrahydrofuran ester l l a (45%) is obtained as a colorless oil. IH NMR (400 MHz, CDC13) (mixture of diastereomers): 6 7.41-7.22 (m, 5H), 5.02 (t, J = 7.4 Hz) and 4.87 (dd, J = 6.0, 9.6 Hz) (total lH), 4.34 (t, J = 8.2 Hz) and 4.29 (dd, J = 6.0, 8.8 Hz) (total lH), 4.11 (t, J = 8.8 Hz) and 4.05 (t, J = 7.4 Hz) (total lH), 3.74 (s) and 3.71 (s) (total 3H), 3.27 (m, lH), 2.68-2.55 (m, lH), 2.20-2.02 (m, 1H). 13CNMR (75 MHz, CDC13) (mixture of diastereomers): 6 174.9, 174.5, 142.6,142.0, 129.0, 128.9,128.2, 128.1, 126.5,126.2,82.0,81.1, 70.9, 70.6, 52.4, 44.9, 44.1, 38.4, 38.0. IR (neat film): 2970, 2890, 1735, 1635, 1435, 1367, 1273, 1197, 1172, 1060, 1020,

748, 695 cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 207 (M 1, 511, 205 (26), 189 (121, 175 (12), 163 (281, 162 (621, 145 (141, 137 (111,133 (161, 131 (261, 129 (141, 125 (15), 123 (23), 119 ( l l ) , 117 (16), 113 (1001, 112 (221, 111 (34), 109 (26), 103 (11),101(13). HRMS (CI, isobutane): calcd for C12H1503 (M 11,207.1021; found, 207.1052. Tetrahydrofuran Ester l l b : 43% yield (54 mg, 0.22 mmol, 1.2:l). IH NMR (400 MHz, CDC13) (mixture of diastereomers): 6 8.22 (s) and 8.21 (s) (total lH), 8.13 (d, J = 7.6 Hz, lH), 7.70 (d, J = 8.0 Hz) and 7.65 (d, J = 7.6 Hz) (total lH), 7.51 (m, lH), 5.10 (t,J = 7.2 Hz) and 4.97 (dd, J = 7.2, 8.8 Hz) (total lH), 4.37 (t,J = 8.4 Hz) and 4.31 (dd, J = 6.8, and 8.8 Hz) (total lH), 4.11 (m, lH), 3.75 (s) and 3.70 (s) (total 3H), 3.36-3.22 (m, lH), 2.77-2.63 (m, lH), 2.19-1.97 (m, 1H). 13CNMR (75 MHz, CDC13) (mixture of diastereomers): 6 174.4, 174.1, 149.1, 149.1, 145.0, 144.6, 132.5, 132.3, 130.0, 123.1, 123.0, 121.5,121.1,80.7,79.9,71.1,70.9,52.5,44.8,44.1,38.1, 38.1. IR (neat film) (mixture of diastereomers): 2970, 2892, 1735,1527,1435,1349,1270,1198,1171,1065,1018,805,730 cm-l. MS (CI, isobutane) (mixture of diastereomers): mlz 252 (M 1, loo), 250 (31, 236 (3), 235 (31, 234 (101, 222 (71, 220 (3). HRMS (CI, isobutane): calcd for C12H1405 (M + 11, 252.0872; found, 252.0854. Tetrahydrofuran Ester llc: 45% yield (53 mg, 0.23 mmol, 1.2:l). IH NMR (400 MHz, CDC13) (mixture of diastereomers): d 7.26 (m, 2H), 6.94-6.80 (m, 2H1, 5.00 (t, J = 7.2 Hz) and 4.86 (dd, J = 6.8, 9.6 Hz) (total lH), 4.33 (t, J = 8.2 Hz) and 4.28 (dd, J = 6.8, 8.8 Hz) (total lH), 4.10 (t, J = 8.4 Hz) and 4.04 (dd, J = 6.8, 8.8 Hz) (total lH), 3.81 (s, 3H), 3.74 (s) and 3.70 (s) (total 3H), 3.26 (m, lH), 2.67-2.55 (m, lH), 2.19-2.01 (m, 1H). 13CNMR (75 MHz, CDC13) (mixture of diastereomers): 6 174.8, 174.5, 160.5, 144.3, 143.7, 130.1, 130.0, 118.8,118.4, 113.8,113.5, 111.8, 111.6,81.8,80.9,70.9, 70.6, 55.5, 52.4, 52.3, 44.8, 44.1, 38.3, 38.0. IR (neat film) (mixture of diastereomers): 2960, 1735, 1602, 1435, 1360, 1260,1195,1168,1042,855,778,692cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 237 (M 1, 1001, 236 (221, 235 (13),230 (6), 219 (211, 205 (61, 175 (71, 159 (71, 135 (81, 129 (12), 113 (9). HRMS (CI, isobutane): calcd for C13H1704 (M l), 237.1127; found, 237.1077. Tetrahydrofuran Ester lld: 19% yield (20 mg, 0.094 mmol, 1.51). 'H NMR (400 MHz, CDC13): 6 4.04-3.90 (m, 2H), 3.69 (s, 3H), 3.13 (m, lH), 2.06-1.94 (m, 2H), 1.84 (m, lH), 1.74-1.26 (m, 11H). 13CNMR (75 MHz, CDC13) (mixture of diastereomers): 6 174.8, 87.3, 68.5, 52.1, 44.3, 41.9, 40.5, 40.0, 29.4, 29.3, 23.0, 22.9. IR (neat film): 2930, 2862, 1738, 1435, 1263, 1195, 1172, 1053 cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 213 (M 1, loo), 212 (23), 191 (13), 181 (30), 163 (191, 162 (42), 131 (231, 129 (121, 113 (84), 112 (18), 111 (311, 109 (94), 101 (16). HRMS (CI, isobutane): calcd for C12H2103 (M + 11, 213.1491; found, 213.1475. Tetrahydrofuran Ester lle: 20% yield (22 mg, 0.10 mmol, 1.5:l). 'H NMR (400 MHz, CDC13) (mixture of diastereomers): d 7.40-7.20 (m, 5H), 4.26-4.03 (m, 2H), 3.69 (s) and 3.57 (s) (total 3H), 3.31 (m) and 3.00 (m) (total lH), 2.612.52 (m, 1H), 2.42-2.29 (m, lH), 1.58 (s) and 1.51 (s) (total 3H). 13C NMR (75 MHz, CDC13) (mixture of diastereomers): d 174.6, 173.9, 147.9, 147.3, 128.9, 128.8, 127.3, 127.2, 125.2, 125.1, 85.8, 85.3, 69.4, 69.3, 52.3, 52.1, 44.8, 44.3, 43.0, 42.8, 29.9, 29.9. IR (neat film) (mixture of diastereomers): 3070, 2990,2964,2940,1735,1685,1639,1440,1265,1198,729,699 cm-l. MS (CI, isobutane) (mixture of diastereomers): mlz 221 (M 1, loo), 205 (241,203 (141,189 (71,151 (91,143 (16), 133 (9), 119 (ll),117 (7). HRMS (CI, isobutane): calcd for C13H1703 (M l),221.1178; found, 221.1189. Representative Procedure for ZnCl2-Catalyzed [3 21-Cycloadditions. To a solution of 4-nitrobenzaldehyde (151 mg, 1.0 mmol) and ZnClz (0.15 mL, 1 M in CH2C12,0.15 mmol) in CHzClz (5 mL) is added a freshly-prepared solution of 1 (5 mL, 0.5 M, 2.5 mmol) under an argon atmosphere. The reaction is stirred a t rt for 14 h and then added dropwise over a 30 min period to a solution of ceric ammonium nitrate (4.1

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Organometallics, Vol. 14, No. 10,1995 4719

Allyl(cyclopentadienyl)iron(II) Dicarbonyls g, 7.5 mmol) in CH30H (20 mL) at -78 "C under a CO atmosphere. After the solution is stirred at -78 "C for an additional 30 min, the solvent is warmed to rt and allowed to stir for an additional 30 min and then evaporated in vacuo. The residue is triturated several times with small portions of CHzCl2 until the washings are colorless, and the washings are transferred to a Si02 flash column and eluted with CHzClz and then 2% acetone in CH2C12. Purification by a second flash column affords 178 mg of tetrahydrofuran ester l l f (71%,3.1:l mixture of diastereomers) as a pale yellow oil. lH NMR (400 MHz, CDCl3): major isomer, 6 8.21 (d, J = 8.8 Hz, 2H), 7.50 (d, J = 8.8 Hz, 2H), 5.11 (t, J = 7.8 Hz, lH), 4.36 (t, J = 8.3 Hz, lH), 4.10 (dd, J = 5.9, 8.8 Hz, lH), 3.75 (s, 3H), 3.25 (m, lH), 2.74 (m, lH), 1.98 (dt, J = 12.7,8.8Hz, 1H);minor isomer, 6 8.21 (d, J = 8.8 Hz, 2H), 7.52 (d, J = 8.8 Hz, 2H), 4.98 (dd, J = 6.8, 8.8 Hz, lH), 4.31 (dd, J = 5.9, 8.8 Hz, lH), 4.14 (t, J = 8.8 Hz, lH), 3.69 (s, 3H), 3.31 (m, lH), 2.66 (m, lH), 2.13 (dt, J = 14.7,8.8 Hz, 1H). 13CNMR (75 MHz, CDCl3) (mixture of diastereomers): 6 174.4, 174.1, 150.3, 150.0, 147.9, 127.1, 126.8, 124.2, 80.7, 80.0, 78.0, 71.1, 71.0, 52.5,44.6,44.0, 38.1, 38.0. IR (neat film) (mixture of diastereomers): 2960, 1735, 1605,1520,1436,1348,1273,1200,1173,1072,1009,912,853, 726 cm-l. MS (CI, isobutane) (mixture of diastereomers): mlz 252 (M 1, loo), 251 (3), 236 (3), 234 (71, 222 (a), 129 (5). HRMS (CI, isobutane): calcd for C12H1405N (M l ) , 252.0872; found, 252.0895. Anal. Calcd for C12H1305N: C, 57.37; H, 5.22. Found: C, 57.38; H, 5.27. Tetrahydrofuran Ester lla: 36% yield (75 mg, 0.36 mmol, 2.1:l mixture of diastereomers). Tetrahydrofuran Ester llb: 62% yield (156 mg, 0.62 mmol, 2.7:l mixture of diastereomers). Tetrahydrofuran Ester llg: 31% yield (73 mg, 0.31 mmol, 2.0:l mixture of diastereomers). lH NMR (400 MHz, CDCl3) (mixture of diastereomers): 6 7.48 (d, J = 7.6 Hz) and 7.39 (d, J = 6.8 Hz) (total lH), 7.24 (m, lH), 6.95 (m, lH), 6.86 (d, J = 7.6 Hz, lH), 5.28 (t,J = 6.8 Hz) and 5.16 (dd, J = 6.8, 8.8 Hz) (total lH), 4.34 (t, J = 7.8 Hz) and 4.27 (dd, J = 6.8, 8.8 Hz) (total lH), 4.10 (t, J = 8.4 Hz) and 4.04 (t, J = 7.8 Hz) (total lH), 3.82 (s) and 3.82 (s) (total 3H), 3.73 (s) and 3.68 (s)(total 3H), 3.31-3.14 (m, lH), 2.70 (m, lH), 2.04-1.97 (m, 1H). I3C NMR (75 MHz, CDC13) (mixture of diastereomers): 6 174.8, 174.6,156.9, 156.8,131.5, 130.9, 128.8, 126.3, 126.1, 121.2, 121.0, 110.7, 110.7, 76.7, 70.7, 70.2, 55.6, 52.3, 44.9, 44.1, 37.0, 36.7. IR (neat film) (mixture of diastereomers): 2960, 1735, 1600, 1490, 1460, 1436, 1365,1280, 1240, 1196, 1173, 1065, 1020, 927, 750 cm-'. MS (CI, isobutane) (mixture of diastereomers): mlz 237 (M 1,71,236 (12), 235 ( l l ) , 219 (48), 205 (M 1 - CHsOH, 19), 187 (55), 177 (39), 176 (21), 175 (31), 162 (15), 159 (41), 150 (30), 145 ( l l ) , 135 (24), 130 (24), 129 (loo), 109 (11). HRMS (CI, isobutane): 1 - CHsOH), 205.0865; found, calcd for C12H1303 (M 205.0865.

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General Procedure for ZnClz-Promoted 13 + 23-Cycloadditions. This procedure is the same as that above

except 1 molar equiv of ZnClz is employed. Tetrahydrofuran Ester lla: 40% yield (82 mg, 0.40 mmol, 1.1:l mixture of diastereomers). Tetrahydrofuran Ester llf: 50% yield (125 mg, 0.50 mmol, 1.1:lmixture of diastereomers). Tetrahydrofuran Ester llg: 28% yield (57 mg, 0.28 mmol, 1.2:l mixture of diastereomers). Tetrahydrofuran Ester llh: 16% yield (38 mg, 0.16 mmol, ratio not determined due to overlapping signals in the lH NMR spectrum). 'H NMR (400 MHz, CDC13) (mixture of diastereomers): 6 7.25 (m, 5H), 4.12-3.76 (m, 3H), 3.68 (s), 3.68 (s), 3.67 (s), and 3.65 (s) (total 3H), 3.14-2.70 (m, 2H), 2.33-1.67 (m, 2H), 1.36 (overlapping d, J = 7.0 Hz) and 1.27 (overlapping d, J = 7.0 Hz) (total 3H). 13C NMR (75 MHz, CDCl3) (mixture of diastereomers): 6 175.0, 175.0, 174.8, 174.7, 144.8, 144.5, 129.1, 128.9, 128.9, 128.4, 128.3, 128.3, 128.2, 127.1,127.0,127.0,85.4,84.9,84.4,84.0,70.6,70.5,70.3, 70.2, 52.3, 52.2, 45.4, 45.3, 44.8, 44.6, 44.4, 44.0, 34.6, 33.8, 33.7, 33.4, 19.1, 18.8, 18.3, 17.9. IR (neat film) (mixture of

diastereomers): 2970, 2884, 1735, 1448, 1370, 1266, 1197, 1170, 1065, 1015, 925, 755, 696 cm-l. MS (CI, isobutane) (mixture of diastereomers): mlz 235 (M 1,22), 223 (25),217 (ll),203 (591, 185 (12), 157 (73), 131 (12), 129 (22). HRMS (CI, isobutane): calcd for C14H1903 (M l), 235.1334; found, 235.1327.

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Representative Procedure for TiCl&atalyzed [3 + 21-Cycloadditions. To a solution of Tic14 (2.0 mL, 1 M

solution in CHzC12, 2 mmol) in CH2Cl2 (5 mL) is added cycloheptanone (112 mg, 1.0 mmol) via a syringe at -78 "C, followed by slow addition (10 min) of a freshly-prepared solution of 1 (5 mL, 0.5 M, 2.5 mmol) under an argon atmosphere. The reaction is warmed to rt, anhydrous CH3OH (2 mL) is added to dissolve the viscous residue, and the dark red solution is added dropwise over a 30 min period to a solution of ceric ammonium nitrate (4.1 g, 7.5 mmol) in CH3OH (20 mL) at -78 "C under a CO atmosphere. After the mixture is stirred a t -78 "C for an additional 30 min, the solvent is warmed to rt and allowed to stir for an additional 30 min and then evaporated in vacuo. The residue is triturated several times with small portions of CHzClz until the washing is colorless, and the washings are transferred to a Si02 flash column and eluted with CH2Cl2 and then 2% acetone in CH2C12. Purification by a second flash column affords 79 mg of tetrahydrofuran ester l l d (37%) as a colorless oil. Tetrahydrofuran Ester lle: 15% yield (33 mg, 0.15 mmol, 1.O:l mixture of diastereomers). Tetrahydrofuran Ester llh: 15% yield (35 mg, 0.15 mmol).

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RepresentativeProcedure for Uncatalyzed [3 21-Cycloadditions. To a solution of 4-nitrobenzaldehyde (151 mg, 1.0 mmol) in CHzCl2 (5 mL) is added a freshly-prepared solution of 1 (5 mL, 0.5 M, 2.5 mmol) under an argon atmosphere. The reaction is stirred at rt for 43 h and then added dropwise over a 30 min period to a solution of ceric ammonium nitrate (4.1 g, 7.5 mmol) in CH30H (20 mL) at -78 "C under a CO atmosphere. After the mixture is stirred at -78 "C for an additional 30 min, the solvent is warmed to rt and allowed to stir for an additional 30 min and then evaporated in vacuo. The residue is triturated several times with small portions of CHzClz until the washings are colorless, and the washings are transferred to a Si02 flash column and eluted with CHzCl2 and then 2% acetone in CH2C12. Purification by a second flash column affords 150 mg of the tetrahydrofuran ester l l f (60%, 1.9:l mixture of diastereomers) as a pale yellow oil. TetrahydrofuranEster lla: 8%yield (17 mg, 0.08 mmol, 1.8:l mixture of diastereomers). Tetrahydrofuran Ester llb: 45% yield (113 mg, 0.45 mmol, 1.9:1 mixture of diastereomers).

Representative Procedure for [3 + 21-Reactions of N-Tosylimines. To a stirred solution of benzaldehyde N-

tosylimine (259 mg, 1.0 mmol) and ZnCl2 (0.15 mL, 1M Et20, 0.15 mmol) in CHzClz (5 mL) is added a 0.5 M solution of freshly-prepared 1 (5 mL, 2.5 mmol) under an argon atmosphere. The mixture is stirred at rt for 24 h and then added dropwise over a 30 min period t o a methanolic solution (15 mL) of ceric ammonium nitrate (3.0 g, 5.5 mmol) at -78 "C under a CO atmosphere. After the mixture is stirred at -78 "C for an additional 30 min, the solution is warmed t o rt and allowed to stir for an additional 30 min and then evaporated in vacuo. The residue is triturated several times with CH2Cl2 (5 mL), and then the washings are transferred to a Si02 flash column and elute with CHzCl2 and then 5% acetone in CH&. Additional purification by a second lash column affords 197 mg (55%) of pyrrolidine ester 13a as a 2 5 1 mixture of diastereomers. lH NMR (400 MHz, CDC13): 6 7.69 (d, J = 8.8 Hz, 2H), 7.34-7.28 (m, 7H), 4.88 (m, major) and 4.75 (t, J = 8.0 Hz, minor) (total lH), 3.89 (m, lH), 3.75 (m, minor) and 3.58 (buried, major) (total lH), 3.59 (s, minor) and 3.58 (s, major) (total 3H), 3.10 (pent, J = 8.0 Hz, major) and 2.85 (pent, J = 8.0 Hz, minor) (total lH), 2.44 (buried, minor)

Jiang et al.

4720 Organometallics, Vol. 14, No. 10, 1995

After being stirred for 1h a t 0 "C, a solution of HBFd (2.9 mL, and 2.06 (m, major) (total lH), 2.44 (s, major) and 2.43 (s, 21.5 mmol) and Ac20 (4.5 mL) is added dropwise to the mixture minor) (total 3H), 2.15 (m, 1H). at 0 "C. The yellow solid is precipitated by addition of Et20 Pyrrolidine Ester 13b: 42% yield (170 mg, 0.42 mmol). (100 mL). Complex 18 (2.49 g, 70%) is collected by vacuum IH NMR (400 MHz, CDC13): 6 8.14-8.06 (m, 2H), 7.75-7.50 filtration, washed with EtzO, and dried under vacuum. 'H (m, 4H), 7.34-7.30 (m, 2H), 4.91 (dd, J = 8.0, 4.0 Hz, major) NMR (400 MHz, acetone-&): 6 5.90 (s,5H), 5.28 (m, lH), 4.05 and 4.80 (t,J = 8.0 Hz, minor) (total lH), 3.96 (m, lH), 3.82 (dd,J=2.5,8.8Hz,lH),3.63(dd,J=2.5,14.6Hz,lH),2.51 (m, minor) and 3.63 (buried, major) (total lH), 3.61 ( 8 , minor) (m, 2H), 2.41 (m, 2H), 1.90-1.20 (m, 13H). 13CNMR (75 MHz, and 3.58 (s, major) (total 3H), 3.09 (pent, J = 8.0 Hz, major) CDCl3): 6 217.1,210.2,208.8,89.5,88.7,54.8,54.7,52.0,43.2, and 2.79 (pent, J = 8.0 Hz, minor) (total lH), 2.56 (m, minor) 43.2, 37.1, 31.8, 31.8, 31.6, 30.4, 30.3, 29.6, 29.6, 28.8, 28.7, and 2.35 (m, major) (total lH), 2.44 (s, major) and 2.43 (s, 24.6, 24.5. IR (CH2Clz): 3125, 3065, 2940, 2870, 2070, 2030, minor) (total 3H), 2.17 (m, minor) and 2.06 (m, major) (total 1695, 1050 (br) cm-l. MS (FAB, glycerol): mlz 357.0 (26) (M 1H). - BF4-), 181.1 (2) (M 1 - Fp+ - BF4-), 177.0 (Fp+). Similarly, pyrrolidine esters 13c were prepared from croPreparation of Tricyclic Furan Ester 20. To a suspentyliron complex 12. sion of yellow complex 18 (444 mg, 1.0 mmol) in CHzCl2 (10 Pyrrolidine Ester 13c: 28% yield (117 mg, 0.28 mmol). mL) is added Et3N (0.2 mL, 1.4 mmol) at 0 "C. The mixture lH NMR (400 MHz, CDC13): 6 8.14-8.06 (m, 2H), 7.75-7.49 is stirred at 0 "C for 30 min and then at rt for an additional (m, 4H), 7.30-7.23 (m, 2H), 4.85 (m, lH), 4.15 (m, minor) and 30 min. After solvent is removed in umuo, the residue is 4.01 (m, major) (total lH), 3.82 (m, minor) and 3.55 (m, major) triturated with Et20 (3 x 10 mL). The ethereal layers are (total lH), 3.69 (s, minor) and 3.67 (s, major) (total 3H), 2.80 combined and evaporated in uacuo t o afford u-complex 19 (263 (m, lH), 2.46 (m, lH), 2.42 (s,major) and 2.40 (s, minor) (total mg, 73%) as a dark brown oil. ZnCl2 (0.15 mL, 1 M in CH23H), 0.99 (d, J = 6.8 Hz, minor) and 0.60 (d, J = 6.8 Hz, major) Cl2, 0.15 mmol) is added t o a-complex 19 in CHzClz (10 mL) (total 3H). at -20 "C. A yellow precipitate is formed immediately. After Preparation of Epoxyketone 17. To a solution of diiso42 h at -20 "C, the mixture is stirred at rt for an additional propylamine (4.6 mL, 35 mmol) in THF (30 mL) is added 1.5 h. The brown solution is transferred to a solution of ceric slowly a solution of "BuLi (18.0 mL, 1.6 M in hexane, 28.8 ammonium nitrate (2.75 g, 5 mmol) in CH30H (15 mL) via a mmol) at 0 "C, followed by the addition of cycloheptanone syringe pump at -78 "C under a CO atmosphere over 30 min. cyclohexylimine (4.257 g, 22 mmol) in THF (10 mL) over 15 The mixture is stirred at -78 "C for 30 min and at rt for an min. The yellow solution is stirred at 0 "C for 30 min. HMPA additional 30 min. After evaporation in uacuo, the residue is ( 5 mL, 29 mmol) is added, followed by the slow addition of triturated with small portions of CHzCl2 and transferred 5-bromopentene (4.33 g, 29 mmol) in THF (10 mL). After being to a flash column. Purification by flash chromatography stirred for 1 h at 0 "C, the reaction is quenched with Et20 (silica gel, CH2Clz) affords tricyclic furan ester 20 (71 mg, (100 mL). The mixture is washed with saturated NH4Cl 30% fm iron-olefin n-complex 18,2.3:l mixture of diasteresolution (3 x 25 mL), and dried over MgS04. Solvent is omers) as a colorless oil. Data for the major isomer are as evaporated in uacuo and purified by flash chromatography follows. 'H NMR (400 MHz, CDC13): 6 4.09 (dd, J = 7.8, 8.8 (silica gel, 50% pentane:CHzClz) to afford 3.29 g (83%)of 244'Hz, lH), 3.87 (t, J = 8.8 Hz, lH), 3.69 (s, 3H), 2.74 (m, lH), penteny1)cycloheptanone as a light yellow oil. IH NMR (400 2.47 (m, lH), 2.02-1.86 (m, 4H), 1.86-1.72 (m, 2H), 1.60MHz, CDC13): 6 5.78 (m, lH), 4.95 (m, 2H), 2.47 (m, 3H), 2.03 NMR 1.52 (m, 3H), 1.50-1.40 (m, 2H), 1.38-1.20 (m, 4H). (m, 2H), 1.85 (m, 4H), 1.70-1.52 (m, 2H), 1.34 (m, 6H). 13C (100 MHz, CDC13): 6 174.0, 98.1, 68.4, 54.8, 51.8, 51.6, 51.3, NMR(75MHz, CDC13): 6 217.0, 139.1, 115.0,52.4,42.9,33.9, 35.9,34.2,32.4,31.6,31.4,29.4,24.1; IR(neat film)2940,2870, 32.0, 31.5, 29.7, 28.6, 26.7, 24.7. IR (neat film): 3090, 2940, 1735, 1636, 1435, 1375, 1325, 1269, 1197, 1168, 1055, 1010, 2870, 1703, 1640, 1449, 1343, 1163, 987, 933, 909 cm-l. 849, 730 cm-'. MS (CI, isobutane): mlz 239.2 (M 1, 441, To the above ketone (2.48 g, 13.76 mmol) in CHzClz (60 mL) 221.2 (lo), 162.0 (15), 135.1 (131, 129.1 (12). HRMS (CI, at 0 "C is added mCPBA (4.15 g, 24.1 mmol) portionwise. The isobutane): calcd for C14H2303 (M 11, 239.1647; found, mixture is stirred at rt for 16.5 h and quenched with H2O (10 239.1628. Data for the minor isomer are as follows. IH NMR mL) and saturated NaHC03 solution (25 mL). The aqueous (400 MHz, CDC13): 6 4.08 (dd, J = 8.8, 9.8 Hz, lH), 3.98 (dd, layer is separated and washed with CHzClz (25 mL). The J = 7.8, 8.8 Hz, lH), 3.67 (s, 3H), 3.13 (dt, J = 9.8, 7.8 Hz, organic layers are combined, washed with brine (25 mL), and lH), 2.41 (dt, J = 10.7, 7.8 Hz, lH), 2.00 (m, lH), 1.90-1.52 dried over MgS04. Evaporation and purification by flash (m, 7H), 1.52-1.30 (m, 7H). 13C NMR (100 MHz, CDC13): 6 chromatography gives 2.24 g (83%) of epoxyketone 17 as a 172.4, 96.8, 66.5, 53.6, 51.9, 51.5, 46.7, 36.8, 34.6, 32.7, 31.6, colorless oil. 1H NMR (400 MHz, CDC13) (mixture of dia27.7, 27.0,23.6. IR (neat film): 2935,2865,1738, 1635, 1435, stereomers): 6 2.89 (m, lH), 2.74 (t, J = 4.4 Hz, lH), 2.651370, 1319, 1273, 1197, 1170, 1054, 1030 cm-l. MS (CI, 2.40 (m, 4H), 1.85 (m, 4H), 1.71 (m, lH), 1.61-1.25 (m, 9H). 13CNMR(75 MHz, CDCl3): 6 216.7,52.4,52.3,52.2,47.1,47.1, isobutane): mlz 239.2 (M 1,281, 221.2 (71, 162.0 (13), 135.1 (51, 113 (8). HRMS (CI, isobutane): calcd for C14H2303 (M 42.9, 42.9, 32.7, 32.5, 32.2, 32.1, 31.5, 31.4, 29.6, 29.6, 28.6, l),239.1647; found, 239.1631. 24.6, 24.6, 23.9, 23.7. IR (neat film): 2940, 2865, 1697, 1447, 930,825 cm-l. MS (CI, isobutane): mlz 197 (M 1,100), 181 (23), 180 (21), 179 (99), 162 (14), 161 (771, 151 (261, 149 (181, Acknowledgment. The donors of the Petroleum 137 (16), 135 (20), 133 (20), 125 (181, 123 (33), 121 (18),119 Research Fund, administered by the American Chemi(16), 113 (19), 112 (15), 112 (711, 111 (291, 111 (16), 110 (ll), cal Society, and the Wendy Will Case Cancer Fund are 109 (73), 107 (361, 105 (20). HRMS (CI, isobutane): calcd for gratefully acknowledged for financial support of this C12H2102 (M l),197.1542; found, 197.1534. research. We also thank Dr. Alicia Regueiro for carryPreparation of Iron-Olefin z-Complex 18. To a freshlying out some informative experiments on the preparaprepared solution of sodium (cyclopentadienyl)iron(II)dicartion of cycloheptanone n-complex 18. bony1 in THF (16 mL, 0.5 M, 8.0 mmol) is added slowly OM940819J epoxyketone 17 (1.57 g, 8.0 mmol) in THF (10 mL) a t 0 "C.

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