Stereospecific rearrangement of 2,2-disubstituted vinylsilane epoxides to the silyl enol ethers of 2,2-disubstituted aldehydes

Abstract

The Z- and E-2-ethyl-2-methylvinylsilane epoxides (5a) and (5b) rearrange stereospecifically in the presence of boron trif luoride–diethyl ether to the Z- and E-silyl enol ethers, (6a) and (6b), respectively, of 2-methylbutanal. These silyl enol ethers react with t-butyl chloride, with 2-phenylthioalkyl chlorides, with the dimethyl acetal of benzaldehyde, with methyl vinyl ketone, and with 2-nitropropene, each catalysed by an appropriate Lewis acid, to give alkylation products. Since the vinylsilanes were prepared by silyl-cupration of a terminal acetylene, followed by alkylation, the overall result is to convert C-2 of a terminal acetylene into the quaternary carbon of a 2,2,2-trialkylated aldehyde, in which each of the alkyl groups is different.