Formation of alpha-Lithio Siloles from Silylated 1,4-Dilithio-1,3-Butadienes: Mechanism and Applications

A full account of a useful transformation from silylated 1,4-dilithio-1,3-butadienes to alpha-lithio siloles is described. These lithio siloles formed by this procedure are general, in terms of substitution patterns and synthetic methods, affording diversified silole derivatives. Notably, some structurally complex molecules, such as bridged bis-silole compounds, have been synthesized easily and successfully by applying our protocol. The structure of the alpha-lithio silole, which adopts a dimeric fashion through two lithium bridges, was confirmed by X-ray analysis. Furthermore, a possible mechanism of the skeleton rearrangements via E/Z isomerization of 1-silyl-1-lithio alkene and nucleophilic attack on silicon is proposed, and is also proved by experimental investigations.