Conformational Effects in the Alkali Metal Reduction of Diaryl Sulfides and Dibenzothiophene

Article abstract of DOI:10.1021/jo00238a022

In alkali metal reductions, the carbon-sulfur bond cleavage that occurs in diaryl sulfides and similar structures such dibenzothiophene is shown to be controlled not by the relative stability of the reactive intermediates but by their degree of conformational freedom.Regardless of the stability of the reactive intermediates, diaryl sulfides suffer carbon-sulfur bond cleavage because the aryl groups are free to assume a configuration that favors cleavage.Dibenzothiophene, although similar in structure to diphenyl sulfide, does not have such freedom and therefore, instead of carbon-sulfur bond cleavage, undergoes ring hydrogenation.The behavior of di-1-naphthyl sulfide and di-4-quinolinyl sulfide support this conclusion and provide further evidence for intramolecular coupling of the aryl moieties at some reactive intermediate stage to form an episulfide type of intermediate.This is then follwed by a double carbon-sulfur bond cleavage to extrude sulfur.