Metal triflimide-mediated acylation of sulfonamides and transacylation of N-acylsulfonamides.

A method for the acylation of sulfonamides and transacylation of N-acylsulfonamides has been developed. The acylation proceeds smoothly in the presence of Cu(NTf2)2 (0.1 mol%) using carboxylic anhydrides, acyl chlorides, or isopropenyl acetate as acylating agents. Alternative catalysts active in this transformation include Zn(NTf2)2, Mg(NTf2)2, La(NTf2)3, and Ce(NTf2)3. The transacylation of N-acylsulfonamides takes place smoothly at room temperature in excess acyl chlorides in the presence of Cu(NTf2)2 (20 mol%) and furnishes analogous N-acylsulfonamides through exchange of the N-acyl group. When performed at elevated temperatures, transacylation also occurs readily in carboxylic anhydrides. The reaction conditions are mild, and a variety of functional groups such as halogen, keto, nitro, cyano, ether, and carboxylic ester are well tolerated. Mechanistic studies using 2,6-di-tert-butyl-4-methylpyridine (DTBMP) as a probe suggest that in situ generated Brønsted acids are the true catalytic species.