Lithiated sulfoxides: α-sulfinyl functionalized carbanions

Abstract

Reactions of alkyl aryl sulfoxides H–CRR′S(O)Ar with n-BuLi–TMEDA (TMEDA = N,N,N′,N′-tetramethylethylenediamine) afforded α-sulfinyl functionalized alkyl aryl lithium compounds of the type [Li₂{CRR′S(O)Ar}₂(TMEDA)₂] (1, R/R′ = H/H, Ar = Ph; 2, R/R′ = H/H, Ar = p-Tol; 3, R/R′ = Me/Me, Ar = Ph; 4, R/R′ = H/Ph, Ar = Ph; 5, R/R′ = Me/Ph, Ar = Ph). The compounds were characterized by ¹H, ¹³C and ⁷Li NMR spectroscopy and, except for 5, by single-crystal X-ray diffraction analyses. In crystals of 1, 2, 3 and 4·Et₂O dinuclear molecules with four-membered Li₂O₂ rings were found. There are no Li⋯C_α contacts, thus, “free” carbanions are the main structural feature. Reactions of 1–6 (6, R/R′ = H/Me, Ar = Ph) with benzaldehyde and benzophenone afforded the corresponding sulfoxides of the type ArS(O)CRR′CHPhOH (1a–6a) and ArS(O)CRR′CPh₂OH (1b–6b), respectively. The reactions yielding 1a/3a and 4b/6b proceeded with high diastereoselectivities. By X-ray diffractometry it has been shown that in the case of 3a and 4b the diastereomers consisting of the two enantiomers S_SR_C and R_SS_C were formed.