Tf 2 O-Mediated Direct Synthesis of 4-Sulfenylated Oxazoles from β-Keto Sulfoxides and Nitriles.

A general and efficient method for the synthesis of 4-sulfenylated oxazoles is described. Trisubstituted oxazoles are obtained in good to excellent yields from β-keto sulfoxides and nitriles. The mechanistic study suggests that the reaction proceeds via the nucleophilic addition of nitriles to the in situ formed α-carbonyl cation followed by intramolecular cyclization.