A new and efficient method for the facile synthesis of N-acyl sulfonamides under Lewis acid catalysis

The N-acylation of sulfonamides with carboxylic acid anhydrides in the presence of Lewis acids is described. Several Lewis acids such as BF3·Et2O, ZnCl2, MoCl5, TiCl4, B(C6F5)3, Sc(OTf)3 and I2 were found to catalyze the reaction efficiently to furnish the N-acylated products in good yields under solvent-free conditions. The reactions of various sulfonamides were studied with different carboxylic acid anhydrides including the less reactive benzoic and pivalic anhydrides, in the presence of 3 mol % ZnCl2 as the catalyst. Carboxylic acids were also successfully used as acylating agents via the mixed anhydride method.