Unexpected Decarboxamidation of α -Arylsulfonyl Weinreb Amides by Grignard Reagents: Synthesis of α -Disubstituted Arylsulfones

An unexpected decarboxamidation of α-arylsulfonyl Weinreb amides as a side reaction under the standard acylating conditions was found in Weinreb amides chemistry. The control experiments for mechanism study disclosed that α-sulfo group was necessary, and α-quaternary carbon was the key factor for the reaction. Meanwhile, an efficient method was established for the preparation of secondary alkyl arylsulfones by this unexpected C―C bond cleavage reaction using excess Grignard reagent.