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Organometallics 1996, 14, 3628-3629
Novel Synthesis of a-StannylVinyl Ethers from Catalytic and Stoichiometric Fischer Carbene Anions Frank E. McDonald,*J Colleen C. Schultz, and Arnab K. Chatterjee Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113 Received May 1, 1995@ Summary: Tributyltin tripate reacts with catalytic molybdenum carbene anion intermediates generated by alkynol cyclization, providing a novel and practical synthesis of a4tributylstannyl)dihydrofurans. Similar reactivity is observed with stoichiometric cyclic and acyclic chromium carbene anions. a-Trialkylstannyl vinyl ethers have proven valuable in synthetic organic chemistry for a variety of carboncarbon bond-forming reactions. For instance, they are commonly used as stable, storable precursors for the corresponding a-lithio vinyl ether derivatives,2 as well as the nucleophilic component for palladium-catalyzed couplings with unsaturated organic halides and sulf o n a t e ~ .However, ~ the usual preparation of a-stannyl vinyl ethers requires highly reactive, pyrophoric bases for deprotonation of vinyl ether precursor^.^ In our studies of molybdenum pentacarbonyl catalyzed cyclizawe have observed tions of alkynols to dihydr~furans,~ that a putative catalytic molybdenum carbene anion intermediate reacts with a variety of stoichiometric electrophiles, including trialkyltin electrophiles. For instance, reaction of photogenerated molybdenum pentacarbonyl triethylamine (25 mol %) with alkynyl alcohol l6 in the presence of 1 equiv of tributyltin chloride gives the 5-(tributylstannyl)-2,3-dihydrofuran 6 (45% yield), the unstannylated dihydrofuran (13%), and unreacted 1;the preparative yield of 6 increases to 65% when the more highly electrophilic tributyltin triflate is employed (Table 1,entry lh7The regiochemistry of this reaction contrasts with that observed with aldehyde ele~trophiles.~~ This methodology is particularly valuable for preparation of substituted stannylated dihydrofurans 6 and 8 in a single step from alkynols 1 and 3,8respectively. @Abstractpublished in Advance ACS Abstracts, August 1, 1995. (1)Camille and Henry Dreyfus New Faculty Awardee, 1992-1997; Alfred P. Sloan Research Fellow, 1995-1997. (2)(a) Soderquist, J. A.; Hsu, G. J.-H. Organometallics 1982,1,830. (b) Hanessian, S.;Martin, M.;Desai, R. C. J . Chem. SOC.,Chem. Commun. 1986,926.(c) Lesimple, P.; Beau, J.-M.; Jaurand, G.; Sinay, P. Tetrahedron Lett. 1986,27,6201.(d) Behling, J. R.; Babiak, K. A.; Ng, J . S.; Campbell, A. L. J . Am. Chem. SOC.1988,110, 2641. (e) (0 Kocienski, Paquette, L.A.; Oplinger, J. A. Tetrahedron 1989,45,107. P.;Barber, C. Pure AppZ. Chem. 1990,62, 1933.( g ) Boeckman, R. K.; Charette, A. B.;Asberom, T.; Johnston, B. H. J . Am. Chem. SOC.1991, 113,5337.(h) Bearder, J . R.; Dewis, M. L.; Whiting, D. A. Synlett 1993, 805.
(3)(a) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986,25,508.(b) Schreiber, S.L.; Porco, J. A. J. Org. Chem. 1989,54,4721.(c) MacLeod, D.; Moorcroft, D.; Quayle, P.; Dorrity, M. R. J.; Malone, J. F.; Davies, G. M. Tetrahedron Lett. 1990,31,6077. (d) Zhang, H.-C.; Brakta, M.; Daves, G. D. Tetrahedron Lett. 1993,34,1571.(e) Friesen, R. W.; Loo, R. W.; Sturino, C. F. Can. J . Chem. 1994,72,1262. (4)For another alternative, see: Casson, S.; Kocienski, P. Synthesis 1993,1133. (5) (a)McDonald, F. E.; Connolly, C. B.; Gleason, M. M.; Towne, T. B.; Treiber, K. D. J . O g . Chem. 1993,58, 6952.(b) McDonald, F. E.; Schultz, C. C. J . A m . Chem. SOC.1994,116,9363. (c) McDonald, F. E.; Gleason, M.M.Angew. Chem., Int. Ed. Engl. 1996,34,350. (6)Brandsma, L.Preparative Acetylenic Chemistry, 2nd ed.; Elsevier: Amsterdam, 1988;p 67.
Primary alkynol substrate 2 had previously appeared t o be unreactive to molybdenum pentacarbonyl mediated cyclizations in the absence of tributyltin electrophiles, as the starting alkynol was largely recovered. We propose that electrophilic trapping apparently drives an unfavorable equilibrium between acyclic vinylidene carbene 11 and cyclic molybdenum carbene anion intermediates 12;reaction of the anionic molybdenum atom with the stannyl electrophile forms the intermediate molybdenum stannyl species 13, which reductively eliminates t o the vinylstannanes 6-8 (Scheme 1).
As the corresponding reaction with stoichiometric Fischer-type carbenes had not been previously rep ~ r t e dwe , ~ then explored kinetic deprotonation of the chromium carbene 45awith n-butyllithium10followed by addition of tributyltin chloride, which also provided the a-stannyl dihydrofuran 6 (Table 1,entry 4). The same product 6 is also obtained under mildly basic conditions (triethylamine, tributyltin triflate, ether, 20 "C;entry 5). This reaction is apparently general, as the acyclic (7)Characterization data for 5: IR (neat) 2961,2081, 1915,1454, 1258,1032 cm-l; lH NMR (300MHz, CDC13) 6 4.76(3H, s), 3.30 (2H, t , J = 7 . 5 ) , 1.54-1.27(4H,m),0.90(3H,t,J=7.5):13CNMR(75MHz. CDC13) 6 362.7,221.6, 215.4,66.5,61.7, 27.4,21.4,12.8;MS 292,264, 236, 208, 180, 152, 107, 93, 80, 52; HRMS calcd for CllH1206Cr 292.0039,found 292.0017.6 IR (neat) 3029,2958,2929,2853, 1584, cm-l; lH NMR (300MHz, 1493,1464,1376, 1259,1055,937,859,697 CDC13)6 7.37-7.18(5H,m), 5.49(lH,dd, J = 10.8,8.0Hz),5.04(lH, dd, J = 2.5,2.0 Hz),3.08 (lH,m), 2.57 (lH,ddd, J = 2.5,8.0,15.01, 1.71-0.88(27H,m); 13C NMR (75MHz,CDC13) 6 162.5,144.4,128.4, z. 436. 127.3.125.8.110.7. , 82.9.39.2. ~ 29.1.27.3. ~ ~ 13.8. , ~9.7: ~. MS ~ ,m.l~ ~ ~ . . , 379. .~ ~~ . ~ 351,-i23,275, 177, 145, 127, 117,91,45; HRMS calcd for c,&60' lzoSn436.1788,found 436.1779.7: IR (thin film, CH2C12) 2953,2655, 1561,1464 cm-l; lH NMR (300MHz,CDCld 6 5.06 (lH, t. J = 2.4 Hz),4.22(2H,t,J=9.6H~),2.56(2H,dt,J=2.4,9.6Hz),1.58-0.82 (27H,m); 13C NMR (75MHz, CDC13) 6 162.4,111.5,69.8,29.9,28.9, 27.2,13.6,9.5;MS m l z 303,247, 191,159,121,69,41;HRMS calcd for C16H320120Sn360.1475,found 360.1467.8: IR (thin film, CH2C12) 2956, 2854,1579,1463 cm-l; lH NMR (300MHz, CDC13) 6 5.02 (lH, d, J = 2.4Hz), 4.30(lH,dd, J = 9.6,g.OHz), 3.78(lH, dd, J = 8.4,7.6 Hz), 2.96 ( l H , m), 1.61-0.87 (30H,m); 13C NMR (75 MHz, CsD6) 6 162.4,118.9,77.4,37.8,29.5,27.6,21.1,14.0,10.0;MS m l z 372,317, 261, 205, 173, 121, 83; HRMS calcd for C17H340116Sn 370.1627, found 370.1602.9IR (neat) 2697,1616,1463,1366,1210,1146,1101 cm-I; 'H NMR (300MHz, CDC13) 6 5.23 (lH, t, J = 7.51,3.45 (3H, SI, 1.88 (2H, q, J = 7.5),1.58-0.68(32H,m); 13CNMR (75MHz, CsD.5) 6 166.1,111.4,54.5,32.3,29.4,27.6,25.2,13.8,10.6;MS m l z 333,301, 265, 235, 209, 177, 151, 121,99,57; HRMS calcd for C l s H 3 ~ 0 ~ ~ ~ S n 386.1940,found 386.1951.The a-stannyl vinyl ethers 6-9 are moderately sensitive to moisture and did not provide satisfactory combustion analyses. (8)Gerard, F.; Miginiac, P. Synth. Commun. 1976,6 , 461. (9)Addition of trialkylstannyl hydrides to group VIB Fischer carbenes gives a-(alkoxyalky1)stannanes.(a) Connor, J. A.; Rose, P. D.; Turner, R. M. J . Organomet. Chem. 1973,55,111.(b) Nakamura, E.;Tanaka, K.; Aoki, S. J . Am. Chem. SOC.1992,114,9715.(c)Merlic, C. A,; Albaneze, J. Tetrahedron Lett. 1996,36,1007,1011.(d) From glycosyldiazirines: Uhlmann, P.; Nanz, D.; Bozo, E.; Vasella, A. Helu. Chim. Acta 1994,77,1430. (10)Casey, C. P.; Brunsvold, W. R. J . Organomet. Chem. 1975,102, 175.
0276-7333/95/2314-3628~09.00/0 0 1995 American Chemical Society
Communications
Organometallics, Vol. 14,No. 8, 1995 3629
Table 1. Reaction of Carbene Anions with Tributyltin Electrophilesa entry
substrate
Scheme 1
product conditions ( ufified ield) 1-3
6-8
’H
I 6 (65%)
7 (64%)
PnBu3r
EtJNH
c H3
:NE13
8 (45%)
Bu3SnX
H
6 (60%) 11
4
5
4 c H 3 0 c ) 5
C
6 (58%)
‘H
HNEt,
In conclusion, these preparations of a-stannyl vinyl ethers represent a novel reaction pathway of Fischer carbene compounds. Further studies t o extend the scope of these reactions and synthetic applications are in progress.
cH30c H
5
12
9 (44%)
a Procedure A: Mo(CO)6 (0.25mmol) was placed in a 18 x 150 mm borosilicate test tube; freshly distilled Et3N (3 mL) and Et20 (10 mL) were added and the contents dissolved by stirring. The reaction mixture was then photolyzed for 20 min under N2. The reaction vessel was removed from the light source, alkynyl alcohol 1-3 (1.0 mmol) was added, followed by n-Bu3SnOTf (1.0 mmol) in Et20 (2 mL), and the reaction mixture was stirred for 18 h. a-Stannyl dihydrofuran products 6-8 were isolated by evaporation of solvent followed by flash chromatography on silica gel (pentane/ EtzO/l% Et2NH). Procedure B: Chromium carbene 4 was dissolved in THF and the solution was cooled to -78 “C. n-BuLi (1.0 equiv, 2.5 M in hexane) was added dropwise; after the mixture was stirred for 30 min n-BusSnC1 was added and this reaction mixture was warmed to room temperature. a-Stannyl vinyl ether 6 was purified by evaporation of solvent followed by flash chromatography on silica gel (pentaneiEtzO/l% EtZNH). Procedure C: Chromium carbenes 4 and 5 (0.5 mmol) were dissolved in freshly distilled Et3N (1mL) and Et20 (5 mL), n-BusSnOTf (0.65 mmol) in Et20 (2 mL) was added, and the reaction mixture was stirred for 4 days. a-Stannyl vinyl ether products 6 and 9 were isolated by evaporation of solvent followed by flash chromatography on silica gel (pentane/EtzO/l% Et2NH).
chromium carbene 5 also gives the vinyl ether g7 as a single stereoisomer (entry 6).11
Acknowledgment is made t o the donors of the Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research. We also gratefully acknowledge financial support provided by Northwestern University and the Camille and Henry Dreyfus Foundation. OM950316T (11)(a) Stereochemistry for 9 is assigned as 2 (tin cis to propyl), consistent with observed NOE enhancement of the vinylic hydrogen resonance (8 5.23)upon irradiation of the methoxy protons (6 3.45). The reaction of chromium carbene 5 with triethylamine in diethyl ether in the absence of tributyltin electrophile gives a mixture of vinyl ether isomers (trans, JHI-HZ = 13.0 Hz;cis: JHIHZ= 6.6 Hz): 5
4% Et3N in Et20
reflux
*
cH30 H
?ranslcis= 1 . 7 / 1
In contrast, Caseyllb and Soderbergll‘ have observed predominant formation of cis-vinyl ethers and vinyl esters from chromium oxacarbenes. (b) Casey, C. P.; Brunsvold, W. R. Inorg. Chem. 1977,16,391. (c) Soderberg, B.C.; Turbeville, M. J. Organometallics 1991,10,3951.
