Reversal of the Importance of Steric and Electronic Effects in the Base-Promoted α‑Silylation of Sulfides

Abstract

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>i</i>-Pr₃SiCl the <i>trans</i>-α,α′-bis-silylated sulfide is formed. The latter pathway provides ready access to the <i>C</i>₂-symmetric enantiomers of <i>trans</i>-2,5-bis­(triisopropylsilyl)-3,4-benzothiophane