Organometallics 1986,5, 2274-2283
2274
Conclusion In this paper we have reported the synthetic, spectroscopic, and structural investigations of several Pt(I1)substituted indole derivatives. These species were obtained by intramolecular cyclization reactions of an electrophilic isocyanide carbon with the adjacent carbanion of an ylide group generated by nucleophilic attack of a base on the acidic methylene protons of either the free or metal-coordinated isocyanides o-(BF4-R3P+-CH2)C6H4NC. When such ligands are coordinated to Pt(II), these reactions are also metal-promoted since Pt acts as an activating agent for the isocyano function, thus making possible the subsequent action of the otherwise uneffective mild base NEb. Furthermore, the Pt(I1) fragment can be selectively placed in the 1-or 2-position of the indole ring depending on whether the nucleophilic attack of the base on the -CH2PR3: group precedes or follows, respectively, the coordination of the isocyano function to the metal. The heterodifunctional ligands o-(XCH2)C6H4NC(X = organic or organometallic functionality) are being currently investigated with the aim of effecting intramolecular attack at the coordinated isocyanide by changing X or the isocyanide-bound metal. In particular, when X is a metal fragment,g such reactions should lead to novel homo- or heterobinuclear systems with the two metal centers lying in close proximity via base-promoted generation of the metal-substituted carbanion XCH--, which subsequently attacks the appropriately activated metal-coordinated isocyanide. The possibility of generating a transitionmetal-substituted carbanion has been recently demon-
(48) Zinner, G.; Fehlhammer, W. P. Angew. Chem., Int. Ed. Engl. 1985, 24, 979.
Acknowledgment. R.A.M. thanks CNR (Rome) for an operating grant based on a US.-Italy Cooperative Science Program and Prof. R. J. Angelici (Department of Chemistry, Iowa State University) for helpful discussions during a visit to I.S.U. related to this program. R.A.M. is grateful to Dr. L. Weber (Universitat Essen-GHS, Chemie) for correspondence regarding P-ylide-isocyanide transitionmetal chemistry. Technical assistance by Mr. A. Berton (CNR, Padua) is also acknowledged. Registry No. 1, 104241-66-9; 2, 103925-31-1; 3, 104241-68-1; 4,104241-70-5; 5, 104241-72-7; 6,104267-45-0; 7,104267-47-2; 8,
104241-74-9;9,104267-49-4;10,103925-21-9; 11, 104241-76-1; 12, 104241-78-3;13, 104241-80-7; 14, 104241-82-9; 15, 104241-84-1; L', 104292-21-9;L2, 103925-27-5;L3,104292-23-1;L4, 104292-25-3; L5,104292-28-6;AFA, 2258-42-6;trans-[(PCy3)2Pt(CNC6H4-o, C:H3)]BF4, 104292-27-5;c~s-{(PP~~)~P~[N(o-C~H~)C(PP~ , I (H)]C1)BF4,104321-47-3;trarzs-(PPh3)Pt[N(o-C6H4)C(PPh,)C(H)]Cl,, 104241-85-2;cis-(PPh3),PtClZ, 15604-36-1;trans[(PMePh,),Pt(CH&l], 24833-61-2;cis-(Ph2PCH==CHPPhJPtC12, 37410-35-8;cis-[(PPh3)2PtCl]Z(BF4)2,19394-83-3;cis-[(PPhS)PtCl2I2,15349-80-1;tram-[(PMezPh),Pt(CH3)C1],24833-58-7; 98839-59-9; o-(HOCH~)C~H~NHCHO, t~am-[(PCy3)2Pt(CHJC1], 104292-17-3; o - ( C ~ C H ~ ) C ~ H ~ N H C104292-18-4; HO, O(C1CH2)C6H4NC,88644-59-1; o-(C1-Me3P+CHZ)C6H4NC, 104322-35-2;o-(C1-Me2PhPtCH2)C6H4NC,103697-57-0; o-(Br104322-36-3; o-(Br-Ph2MeP+CH2)C6H,NC, Ph3P+CHZ)C6H4NC, 104292-19-5; o-aminobenzyl alcohol, 5344-90-1.
Supplementary Material Available: Listings of hydrogen atom coordinates, bond distances and angles, and thermal parameters (17pages); a list of observed and calculated structural factors (23pages). Ordering information is given on any current masthead page. (49) Crocco, G. L.; Gladysz, J. A. J. Am. Chem. Soc. 1985,107,4103.
Preparation and Reactions of ( E )-a-Lit hio-a- (methytdiphenylsilyl)alkenest Gerald L. Larson,"
Evelyn Torres,'ascCarmen Burgos Morales,1a9d and Glenn J. McGarvey" lb
Departments of Chemistry, University of Puerto Rico, Rio Piedras, P.R. 0093 1, and University of Virginia, Charlottesville, Virginia 2290 1 Received January 28, 1986
Alkylation of (dibromomethy1)methyldiphenylsilaneand thermolysis of the resulting (a,a-dibromoin good yield. These have alky1)silanes in DMF provides the (2)-1-bromo-1-(methyldiphenylsily1)alkenes been converted to their corresponding lithium reagents by metal-halogen exchange. The stereointegrity of these vinyllithium reagents was found to be excellent at temperatures below 0 OC. These lithium reagents were reacted with alkyl halides, group IV (14)chlorides, aldehydes, benzoyl chloride, and acetic anhydride. The synthetic potential of these systems was demonstrated by the preparation of (2)-heneicosene, the pheromone of the house fly (musca dornestica), and of l-phenyl-1,2-butadiene. The Grignard reagents of the vinyl bromides were also studied, but to a lesser extent.
Introduction In conjuction with an interest in investigating the potential of organosilicons optically active at silicon in enantioselective synthesis, studies which currently involve the 1-naphthylphenylmethylsilyl group,2 we have been carrying out several studies with the diphenylmethylsilyl 'Dedicated to Dr. George Zweifel on the occasion of his 60th birthday.
0276-7333/86/2305-2214$01.50/0
group, which serves as a reasonable, readily available model for the 1-naphthylphenylmethylsilylgroup. We wish to report herein on the preparation of and some of the (1) (a) University of Puerto Rico. (b) University of Virginia. (c) National Science Foundation Predoctoral Fellow, 1983-1986. (d) Graduate student supported in part by the NIH-MBRS (RR-8102-14) program. Current address, The Upjohn Co., Kalamazoo, MI. (e) Current address: Petrarch Systems, A member of Dynamit Nobel Chemicals, Bartram Rd, Bristol, PA 19007. (2) Larson, G. L.; Torres, E. J . Organornet. Chem. 1985, 261, 19.
0 1986 American Chemical Society
Reactions of (E)-a-Lithio-a-silylalkenes entry
Table I. PreDaration of 7. 1. and 2 R'CH2X % yield 7O C,HJ 84 n:c4i-I9I 82
R3Si Ph?MeSi PhiMeSi Ph2MeSi PhzMeSi PhMe2Si PhMezSi PhMe2Si
1 2 3 4 5 6 7
Organometallics, Vol. 5, No. 11, 1986 2275
79 78 77 81 58
n-C12H231
C3H5Br CzH51 C3H5Br PhCHzBr
% yield 1 or 2"
Z E ratiob
86 71 78c 41 54 95 81
982 982 95:5 95:5 91:9 66:34 98:2
a Isolated yields. Products purified by silica gel chromatography or crystallization. Ratio determined by capillary GLC on a 25-m FFAP or 25-m SE-30 column (1%)or by 'H NMR spectroscopy (5%). CProductprepared from crude alkylated product. Yield calculated based on starting (dibromomethy1)diphenylmethylsilane.
Scheme I R3SiCl
LiCHBr2
R3SiCHBr2
THF/-90%
1 . LDAlTHF
2. R ' C H x~
* R3SiCBr2CH2R'
7
DMF
reflux
8
R
Br
chemistry derived from the (2)-(a-bromoviny1)silanes 1 and to a lesser extent the dimethylphenylsilyl analogue 2. PhZMeSi
H
PhMepSi
X
X
Br
R
Br
la, R=Me
b. R = P h c , R = CH=C H Z d. R = n -C11 He3
P h2 Me S i
H
PhzMeSi
X
R
BrMg
2
#"
Li 4
R
H R
3
1- NpPhMeSi" Y %e 5,Y = Br 6 , Y Li
-
The principle questions that we wanted to address in these studies are (1) how to best prepare compounds of the type 1 in a regiospecific manner, (2) what would be the stereointegrity of their Grignard and lithium reagents, 3 and 4, respectively, (3) what would be the reactivity of 3 and 4 toward alkyl halides and other electrophiles, and finally (4) what would be the results of applying the Grignard and lithium reagents of 5 toward asymmetric ~yntheses.~ Preparation of 1 and 2. Although a variety of methods have been employed in the preparation of compounds of the general type 1 as well as for their E counterparts," we chose to prepare them via the convergent route outlined in Scheme I. (Dibromomethy1)lithium is readily silylated (3) Results on this aspect of the work will be reported in due course. (4) For (a-bromoviny1)silanesconsult (a) Ottolenghi, A.; Fridkin, M.; Zikha, A. Can. J.Chem. 1963,41, 2977. (b) Miller, R. B.; McGarvey, G. J.Org. Chem. 1978,43,4424. Miller, R. B.; McGarvey,G. Ibid. 1978,44, 4623. (c) Zweifel, G.; Lewis, W. Ibid. 1978 44, 2739. (d) Grobel, B.-Th.; Seebach, D. Chem. Ber. 1977,110,867. (e) Seyferth, D.; Lefferts, J. L.; Lambert, R. L., Jr. J. Organomet. Chem. 1977,142,39. For an erratum on this paper consult: Ibid. 1979,168, C32. (0 Yamaguchi, R., Kawasaki, H.; Kawanisi, M. Synth. Commun. 1982, 12, 1027. (g) Yarosh, 0. G.; Voronof, V. K.; Komarov, N. V. Izu. Akad. N a u k SSSR, Ser. Khim. 1971, 875. (h) Komarov, N. V.; Yarosh, 0. G. Ibid. 1971,1573. (i) Boeckman, R. K.; Jr.; Bruza, K. J. Tetrahedron Lett. 1974, 3365. (i) Miller, R. B.; Al-Hassan, M. I. J. Org. Chem. 1983,4113. (k)Brook, A. G.; Duff, J. M.; Reynolds, W. F. J. Organornet. Chem. 1976, 121, 293. (1) Chan. T. H.; Mychajlowskij,W. Tetrahedron Lett. 1974,171. (m) Brook, A. G.; Duff, J. M. Can. J. Chem. 1973, 51, 2024. (n) Villieras, J.; Rambaud, M.; Kirschleger, B.; Tarhouni, R. J. Organomet. Chem. 1980, 190, C31. (0) Chan, T. H.; Mychajlowskij, W.; Ong, B. S.; Harpp, D. N. J. Org. Chern. Chem. 1978,43, 1526. For (a4odovinyl)silanesconsult: (p) Zweifel, G.; Murray, R. E. Ibid. 1981,46,1292. (4)Hasan, I.; Kishi, Y. Tetrahedron Lett. 1980, 22, 4229.
Table 11. Stereointegrity of Lithium Reagents 4a" and Grignard 3abas a Function of Temperature vinylmetallic temp, "C E Z ratio Li -78 95:5 Li -40 91:9 Li -20 91:9 Li 0 91:9 Li 30 87:13 MgBr -78 95:5 MgBr -40 95:5 MgBr -20 95:5 MgBr 0 95:5 MgBr 30 95:5 "Prepared from a 95:5 Z E ratio of la and sec-butyllithium in THF as a 0.5 M solution. bPrepared from 4a and MgBr2 initially at -78 "C.
a t low temperature in good yield to provide the corresponding (dibromomethy1)silane 7 which can in turn be deprotonated and alkylated with alkyl halides to give 8 in good to excellent ~ i e l d . ~These , ~ (a,a-dibromoalky1)silanes tend to lose hydrogen bromide upon standing, and best results are obtained when they are directly converted in crude form to the (a-bromoviny1)silanes 1, 2, or 5 in refluxing dimethylformamide.' This procedure gives predominantly the 2 product in all cases with the more sterically demanding methyldiphenylsilyl group providing the greatest stereoselectivity as can be seen by comparison of entries 1 and 5 and 4 and 6 in Table I. If this reaction is allowed to proceed for an extended period of time, considerable amounts of the ethynylsilane are formed presumably due to the trans arrangement of the vinyl proton and the bromine in the initial elimination product. Considering a trans elimination of hydrogen bromide, it can be argued that the observed product is derived from conformer 9 as opposed to 10. In addition to being the predicted lower energy conformer, 9 holds 2 : l statistical advantage over 10. These results are consistent with those found for the elimination of hydrogen chloride from (a,a-dichloroalky1)silanesin refluxing DMF.7 This sequence was carried out successfully with ethyl iodide, benzyl bromide, allyl bromide, and dodecyl iodide but was not successful with benzyl chloride, allyl chloride, alkyl brom(5) (a) Villieras, J.; Bacquet, C.; Normant, J. F. Bull. Soc. Chern. Fr. 1975, 1797. (b) Seyferth, D.; Lambert, R. L., Jr.; Hanson, E. M. J . Organornet. Chem. 1970, 24, 647. (6) For a comparable procedure in the preparation of alp-diidosilanes consult: Seyferth, D.; Lambert, R. L.; Jr. J. Organornet. Chem. 1973,54, 123. (7) Larson, G. L.; Rosario, 0. J. Organomet. Chem. 1979, 168, 13.
(8) For spectral data on similar systems but containing the trimethylsilyl group consult ref 4b,c,e. (9) Miller, R. B.; McGarvey, G. Synth. Cornrnun. 1979, 9, 831. (10) For examples of other useful a-silylvinylmetallics consult: (a) Sato, F.; Ishikawa, H.; Sato, M. Tetrahedron Lett. 1981, 22, 85. (b) Westmijze, H.; Meijer, J.; Vermeer, P. Ibid. 1977, 1824. (c) Eisch, J. J.; Damasevitz,G. A. J. Org. Chem. 1976,41, 2214. (d) Uchida, K.; Utimoto, K.; Nozaki, H. Ibid. 1976, 41, 2215. (e) Uchida, K.; Utimoto, K.; Nozaki, H. Ibid. 1976, 41, 2941.
2276 Organometallics, Vol. 5, No. 11, 1986 H
Larson et al.
H
I
I
Br
81
10
9
ides, isopropyl iodide, and neopentylmethane sulfonate. The results of the alkylation of the (dibromomethy1)silanes and their elimination to 1 are given in Table I. The assigned Z geometry to the principle isomers of the (a-bromoviny1)silanesformed is based on the results of the elimination of hydrogen chloride from the a,a-dichloroa1kyl)silanes' and the lH NMR spectrum of the vinyl region, which in all cases shows a major resonance a t ca. 6.3 ppm for the Z isomer and a small resonance at ca. 6.9 ppm for the minor E isomer.s It is interesting to note that the vinyl proton in the dimethylphenylsilyl and methyldiphenylsilyl systems resonate at essentially the same place as their trimethylsilyl counterparts. In the butadienes and styrene systems this key proton resonates at ca. 6.9 ppm and in the aromatic region for the Z and E isomers, respectively. Further confirmation of the assigned geometry comes from the attempted isomerization of (Z)-la under conditions employed by Zweifel and Lewis4"to successfully prepare (2)-(a-bromoviny1)trimethylsilanesin high isomeric purity from their E isomers.4c This attempted isomerization provided only starting @)-la.The final isomeric ratios of all systems were determined by capillary GLC on a 30-m SE-30 or a 25-m FFAP column. Preparation and Reactions of 3 and 4. I t was of interest to study both the generation and the stereointegrity of 3 and 4. Treatment of la with magnesium turnings in T H F followed by protonation gave 11 and 12 in excellent yield, but as a 78:22 E Z mixture. On the basis of this result, the Grignard reagent was not further studied. I t is worthwhile noting, however, that the bromomagnesium reagent 3a prepared by treatment of 4a with magnesium bromide at 0 OC maintained its stereointegrity providing 11 and 12 in a 95:5 EZ ratio, the same ratio as the starting vinyl bromide implying that the loss of stereochemistry in 3a occurs during the direct formation of the Grignard reagent and is not a result of the stability of the vinyl Grignard reagent itself. la
I Mg/THF 2 NHqCl(oq) 90%
3.- 0 . C 4. NHqCltoq)
(methyldiphenylsily1)propene. This is to be compared to the results found with [a-(trimethylsilyl)viny1]lithium reagents which provide an equilibrium E:Z mixture of about 86:14 at 0 " C starting from greater than 99% pure (E)-w(trimethylsily1)vinyl i ~ d i d e . ~Itp thus appears that the use of the methyldiphenylsilyl group leads to greater stereointegrity of the vinyllithium reagent. Reaction of 4a with Trimethylchlorosilane, -germane, and -stannane. The metalation of 4a with group IV (14*l) chlorides proceeds in good yield with high stereospecificity according to eq 3. The assignment of the stereochemistry is based on the stereochemistry of the starting lithium reagent as described above.
X
PhpMeSi I . s-BuLI/THF
la
2.Mn5MCI
*
Me3M
H
(3)
Me
13
4 d -t n - C e H 1 7 1
47%
M = Si.Ge.Sn P h pMe Si
TBAF
- Cii H a 3
n-CeH17hn
THF/HMPA
14
15
Alkylation of 4. Generation of 4d from the reaction of Id with a slight excess of sec-butyllithium followed by reaction with methanol gave a 99% yield of 1-(methyldiphenylsily1)-1-tridecene,indicating excellent formation of the lithium reagent. A similar result was observed for the two-step conversion of IC to 1-(methyldiphenylsily1)-1,3butadiene, although the yield was a lower 70%. Lithium reagent 4a was successfully alkylated with ethyl, n-butyl, n-octyl, and n-decyl iodide and with dimethyl sulfate as shown in Table 111. However, it did not react with methyl iodide, allyl chloride, allyl bromide, or benzyl bromide even in the presence of hexamethylphosphoramide or N,N,N',N'-tetramethylethylenediamine. The stereochemical assignments are again based on lH NMR data, which showed essentially a single resonance at 5.85 ppm for the vinyl proton consistent with the results of Zweifel and Lewis,4cMiller and M ~ G a r v e y and , ~ ~ Seyferth and c o - w ~ r k e r s ~This ~ . alkylation procedure was applied to the synthesis of (2)-heneicosene, the major component of the sex pheromone for the house fly (Musca domestica). Thus, lithium reagent 4d was treated with n-octyl iodide to give vinylsilane 14 in 47% yield and greater than 95% stereochemical purity. Protiodesilylation of this material gave 58% of the desired pheromone component, whose isomeric ratio was determined to be greater than 9 8 2 Z:E by 'H NMR analysis of its epoxide.12
- ph2Mes'xH Ph2Mes'xMe
I . s-EuLi/THF/-78 2 . Mg-0,~
la
Table 111. Group IV (14) Metalation and Alkylation of Lithium Reagent 4a entry RX % yield E:Z ratio Me2S04 50 964 95:5 51 C2HJ n-C4H91 95:5 47 n-C8H,,I 95:5 79 95:5 76 n-CloH211 Me3SiC1 42 9O:lO Me3GeCl 92 2:98 Me3SnCl 2:98 85
Me
H
'C
-
+
H
11
12
78%
22 %
95%
5%
H
("
(21
The formation of the lithium reagent was readily accomplished with n-, sec-, or tert-butyllithium in T H F a t -78 0C.9The use of n-butyllithium, however, led to the formation of butylated material via reaction of the la with the 1-bromobutane produced from the metal-halogen exchange as had been found by Miller and McGarvey in similar studies.4b The use of a single equivalent of secbutyllithium or 2 equiv of tert-butyllithium provided excellent entries into the (E)-(a-lithio-a-sily1)alkenes 4. The stereointegrity of these useful reagents'O was studied as a function of temperature via 3a and 4a. The results of this study are given in Table 111. As can be seen these lithium reagents maintain their stereochemistry over a wide temperature range, noteworthy being the conversion of a 95:5 Z E mixture of la to a 91:9 E:Zmixture of 1-
(11) Carlson, D. A.; Mayer, M. S.; Silhacek, D. L.; James, J. D.; Beroza, M.; Bierl, B. A. Science (Washington, D.C.) 1971, 174, 76.
Reactions of (E)-a-Lithio-a-silylalkenes Table IV. Reaction of 4a with Aldehydes and Cyclohexanone with BFaOEtzCatalysis entry carbonyl compd % yield" 16 % yield" 17 1 PhCHO 81 81 2 i-PrCHO 79 56b 3 t-BuCHO C 4 cyclohexanone 72 64 "Isolated yield. All products are greater than 98% 2 isomer. bProduct very volatile analyzed by 'H NMR. cProduct unstable analyzed by lH NMR.
Reaction of 4a with Aldehydes and Ketones. On the basis of the excellent results of the reaction of several [a-(trimethylsilyl)vinyl]lithiumreagents, with and without @-substituents,with aldehydes and ketones4j,'J3we were somewhat surprised to find that lithium reagent 4a reacted very poorly (
