[1,2]- and [1,4]-Wittig rearrangements of α-alkoxysilanes: effect of substitutions at both the migrating benzylic carbon and the terminal sp2 carbon of the allyl moiety

Substituted α-alkoxysilanes can be deprotonated by alkyllithium bases and made to undergo Wittig rearrangements to afford the [1,4]- and [1,2]-rearranged products in varying ratios. Substitution at the benzylic migrating carbon and/or at the allylic carbon of the allyl moiety impacts the rearrangement reaction, influencing the reactivity as well as the [1,4]-/[1,2]-selectivity. Diastereomeric α-alkoxysilanes show different reactivities with the syn diastereomer being the more reactive isomer.