Reduction of Thiocarbonyl Compounds with Lithium Diisopropylamide

Abstract

Treatment of 4,4-disubstituted 2-phenyl-1,3-thiazole-5(4H)-thiones with lithium diisopropylamide (LDA; LiNiPr2) in THF at -78° yielded the corresponding 1,3-thiazole-5(4H)-thioles in moderate yields. Sequential treatment with LDA and MeI under the same conditions led to the 5-methylsulfanyl derivatives. Similarly, reaction of some cycloalkanethiones as well as diaryl thioketones with LDA and MeI gave cycloalkyl methyl sulfides and diarylmethyl methyl sulfides, respectively. A reaction mechanism via H transfer from LDA to the thiocarbonyl C-atom via a six-membered transition state is proposed for this unprecedented reduction of the C1⁄4S bond.