Reversal of the importance of steric and electronic effects in the base-promoted α-silylation of sulfides.

Lithiation of α–C-H groups in organic substrates by RLi or R2NLi followed by silylation with R′3SiCl generally provides analogous products regardless of the R′ group of R′3SiCl. A striking exception using 3,4-benzothiophane as substrate depending on whether R′ is methyl, phenyl, or isopropyl is demonstrated. With R′ = Me or Ph, the geminal α,α-bis-silylated products result whereas with i-Pr3SiCl the trans-α,α′-bis-silylated sulfide is formed. The latter pathway provides ready access to the C2-symmetric enantiomers of trans-2,5-bis(triisopropylsilyl)-3,4-benzothiophane.