Extremely Facile Ligand-Exchange and Disproportionation Reactions of Diaryl Sulfoxides, Selenoxides, and Triarylphosphine Oxides with Organolithium and Grignard Reagents

Article abstract of DOI:10.1021/jo00022a024

Diaryl sulfoxides undergo unusually rapid ligand-exchange reaction upon treatment with organolithium reagents at -95 deg C.Optically pure phenyl p-tolyl sulfoxide (4b) reacted with organolithium reagents at the range from -20 to -95 deg C to give facile ligand-exchange and disproportionation products, i.e., diphenyl sulfoxide (7), recovered 4b, and di-p-tolyl sulfoxide (8) in a statistical ratio of 1:2:1 in quantitative yields, and the recovered 4b was completely racemized.This facile ligand exchange was observed in the similar reactions using only diaryl selenoxides and triarylphosphine oxides.The reactions of 18O-labeled phenyl p-tolyl sulfoxide (4c) with organolithium reagents gave products in a statistical ration without 18O scrambling, indicating that only the C-S bond cleavage took place under low temperature.It is suggested that the ligand exchange reactions occur by the nucleophilic attack by organolithium reagent at the sulfinyl sulfur atom, giving ?-sulfurane as an intermediate that collapses rapidly.These results suggest that the treatment of arylic sulfoxides, selenoxides, and phosphine oxides with strong bases should be effected with caution.