Alpha-lithiosilanes: III. The Reaction of Vinylalkoxysilanes with Organolithium Reagents

The reaction of two equivalents of vinyldimethylethoxysilane or vinyldimethylmethoxysilane with hydrocarbon soluble alkyllithium reagents; $\text{t}$-BuLi, $\text{s}$-BuLi, or $\text{n}$-BuLi; in hexane at low temperature gives high yields of 1,1-dimethyl-2-alkyl-4-(dimethylalkoxysilyl)silacyclobutanes. With methyl- or phenyllithium substituted vinylsilanes are obtained. The stereochemistry of the silacyclobutanes is assigned on the basis of Si-29 and H-1 NMR. For vinyldimethylethoxysilane the ratio of cis to trans silacyclobutane is about $\text{57}\text{43}$, and is independent of the alkyllithium reagent used. In the reaction of vinyldimethylmethoxysilane with $\text{t}$-BuLi a $\text{sol70}\text{30}$ ratio of the cis and trans silacyclobutane is obtained. A pathway is proposed which is consistent with the stereochemical results and with the products isolated in the reaction run in THF.