Reactions of (Triphenylsilyl)ethylene Oxide with Grignard Reagents (and with MgBr 2 ). A Reinvestigation Paul F. Hudrlik,* Mohamed E. Ahmed, Ralph R. Roberts, and Anne M. Hudrlik Department of Chemistry, Howard University, Washington, D.C. 20059 Received March 11, 1996 X Reactions of (triphenylsilyl)ethylene oxide (1) with simple Grignard reagents such as EtMgBr and PhMgBr have been reported to yield crystalline hydroxysilanes assigned as the R-hydroxy silanes expected from  opening of the epoxide. Reinvestigation of these reactions showed that the hydroxysilanes were the -hydroxy silanes 4 and 7 expected from a rearrangement-trapping sequence; a bromohydrin, assigned as the R-bromo--hydroxy silane 9 from R opening, and (triphenylsilyl)acetaldehyde (8) were also formed. Many ring-opening reactions of R,-epoxy silanes are known. In most cases, ring opening occurs at the carbon R to the silicon to give -hydroxy silanes. 1 However, in 1961, the reactions of triphenylsilylethylene oxide (1) with simple Grignard reagents (e.g., EtMgBr, PhMgBr) were reported to give products of  opening (e.g., R-hy- droxy silanes 2 and 5). 2 (Similar reactions were reported for (tribenzylsilyl)ethylene oxide. 2 ) Moreover, the reac- tion of 1 with MgBr 2 to give (triphenylsilyl)acetaldehyde (8) 3 appears to take place by a mixture of R- and -opening pathways: reaction of R-deuterio(triphenylsi- lyl)ethylene oxide with MgBr 2 gave 8 with deuterium scrambled between the aldehyde and R carbons. 4 Most of the studies of ring opening of R,-epoxy silanes have been carried out using trimethylsilyl epoxides. Although the vast majority of ring-opening reactions of R,-epoxy silanes give R opening,  opening has been observed in some other cases as well, e.g., with sterically hindered substrates such as epoxy silanes having the (i- Pr) 3 Si group. 5 Because of the synthetic utility of epoxysi- lanes 1 and because phenyl-substituted silicon groups have been shown to increase the synthetic versatility of organosilicon compounds (phenyl substitution on silicon allows the stereospecific replacement of the silicon group by OH (RSiMe 2 Ph f ROH), 6 we have reinvestigated the reactions of epoxysilane 1 with Grignard reagents and with MgBr 2 . We have previously shown that reactions of Grignard reagents with various R,-epoxy trimethylsilanes give -hydroxy silanes that are isomeric with those expected from direct R opening. 8 The reactions were felt to occur by an R-opening pathway: magnesium halide-promoted rearrangement of the epoxides to R-silyl carbonyl com- pounds and trapping with the Grignard reagents. Bro- mohydrins, shown to be R-bromo -hydroxy silanes, were obtained from some of these reactions using shorter reaction times. 8 The reactions of magnesium halides with R,-epoxy trimethylsilanes have also been studied 9,10 and have resulted in halohydrins, 9a,b,d,f,g R-silyl carbonyl compounds, 9a,c-f and in a few cases, silyl enol ethers 9a,c,f (presumably from rearrangement of the R-silyl carbonyl compounds). In most cases, the products could be ac- counted for by R opening of the epoxy silanes. 11 However, reaction of an R-alkyl-substituted epoxy trimethylsilane with a Grignard reagent gave an R-hydroxy silane (presumably from  opening) along with the expected -hydroxy silane (1:6 ratio). When the reaction was run with added MgBr 2 , the -hydroxy silane was obtained in good yield. 8 Relatively few reactions have been carried out with epoxy silanes having aryl-substituted silicon groups. In addition to the above-mentioned Grignard reactions, other ring-opening reactions of (triphenylsilyl)ethylene oxide (1) include examples of both R and  ring opening. Reactions with LiAlH 4 3a and with (i-Bu) 2 AlH 4,12,13 have been reported to result in R opening; although with a large excess of LiAlH 4 , the product of  opening was observed as a minor product. 3a Reaction with Me 2 CuLi resulted in a mixture with predominant R opening (88: 12), while addition of BF 3 ‚Et 2 O reversed the regioselec- tivity. 14 Reactions with HCl, 4 (i-Bu) 3 Al, 12b lithiated sul- fones, 15 and MeAlCl 2 16 have resulted in predominantly the product of  ring opening. X Abstract published in Advance ACS Abstracts, June 15, 1996. (1) Review: Hudrlik, P. F.; Hudrlik, A. M. In Advances in Silicon Chemistry; Larson, G. L., Ed.; JAI Press: Greenwich, CT, 1993; Vol. 2, pp 1-89. (2) Wende, A.; Gesierich, A. Plaste u. Kautschuk 1961, 8, 301-303; Chem. Abstr. 1962, 56, 5993f. (3) (a) Eisch, J. J.; Trainor, J. T. J. Org. Chem. 1963, 28, 2870- 2876. (b) Wilt, J. W.; Kolewe, O.; Kraemer, J. F. J. Am. Chem. Soc. 1969, 91, 2624-2631. (c) Brook, A. G.; MacRae, D. M.; Bassindale, A. J. Organomet. Chem. 1975, 86, 185-192. (4) Eisch, J. J.; Galle, J. E. J. Org. Chem. 1976, 41, 2615-2621. (5) Lipshutz, B. H.; Lindsley, C.; Susfalk, R.; Gross, T. Tetrahedron Lett. 1994, 35, 8999-9002. (6) (a) Fleming, I.; Henning, R.; Plaut, H. Chem. Commun. 1984, 29-31. (b) Fleming, I.; Sanderson, P. E. J. Tetrahedron Lett. 1987, 28, 4229-4232. (c) The alkoxy group on silicon has also been used for this purpose; see ref 7. (7) Tamao, K.; Najako, E.; Ito, Y. J. Org. Chem. 1987, 52, 4412-4414. (8) Hudrlik, P. F.; Hudrlik, A. M.; Misra, R. N.; Peterson, D.; Withers, G. P.; Kulkarni, A. K. J. Org. Chem. 1980, 45, 4444-4448. (9) (a) Hudrlik, P. F.; Misra, R. N.; Withers, G. P.; Hudrlik, A. M.; Rona, R. J.; Arcoleo, J. P. Tetrahedron Lett. 1976, 1453-1456. (b) Hudrlik, P. F.; Hudrlik, A. M.; Rona, R. J.; Misra, R. N.; Withers, G. P. J. Am. Chem. Soc. 1977, 99, 1993-1996. (c) Obayashi, M.; Utimoto, K.; Nozaki, H. Tetrahedron Lett. 1977, 1807-1810. (d) Obayashi, M.; Utimoto, K.; Nozaki, H. Tetrahedron Lett. 1978, 1383-1386. (e) Obayashi, M.; Utimoto, K.; Nozaki, H. Bull. Chem. Soc. Jpn. 1979, 52, 1760-1764. (f) Obayashi, M.; Utimoto, K.; Nozaki, H. Bull. Chem. Soc. Jpn. 1979, 52, 2646-2652. (g) Okamoto, S.; Shimazaki, T.; Kobayashi, Y.; Sato, F. Tetrahedron Lett. 1987, 28, 2033-2036. (10) (a) Ashwell, M.; Jackson, R. F. W. J. Chem. Soc., Chem. Commun. 1988, 645-647. (b) Hewkin, C. T.; Jackson, R. F. W. Tetrahedron Lett. 1990, 31, 1877-1880. (c) Ashwell, M.; Clegg, W.; Jackson, R. F. W. J. Chem. Soc., Perkin Trans. 1 1991, 897-908. (d) Hewkin, C. T.; Jackson, R. F. W. J. Chem. Soc., Perkin Trans. 1 1991, 3103-3111. (11) An exception is reactions of epoxides substituted in the R position with SO2Ph which usually give (R-bromoacyl)silanes. 10 (12) (a) Eisch, J. J.; Galle, J. E. J. Organomet. Chem. 1988, 341, 293-313. (b) Eisch, J. J.; Liu, Z.-R.; Singh, M. J. Org. Chem. 1992, 57, 1618-1621. (13) The product of  opening was obtained from the reaction of R-methyl(triphenylsilyl)ethylene oxide and (i-Bu)2AlH. 12a (14) Chauret, D. C.; Chong, J. M. Tetrahedron Lett. 1993, 34, 3695- 3698. 4395 J. Org. Chem. 1996, 61, 4395-4399 S0022-3263(96)00485-9 CCC: $12.00 © 1996 American Chemical Society