Copper‐Catalyzed <i>N</i>‐Alkylation of Sulfonamides with Benzylic Alcohols: Catalysis and Mechanistic Studies

Abstract

Abstract The N ‐alkylation of sulfonamides with alcohols is efficiently performed in the presence of easily available copper catalysts via hydrogen borrowing methodology. Applying a copper acetate/potassium carbonate system the reaction of sulfonamides and alcohols gave the corresponding secondary amines in excellent yield. In situ HR‐MS analysis indicated that bissulfonylated amines are formed under air atmosphere, which act as self‐stabilizing ligands for the catalytic system. UV‐visible measurements suggest the interaction between the copper centre and the bissulfonylated amine. Reactions of benzyl alcohol‐ d 7 with p ‐toluenesulfonamide, N ‐benzyl‐ p ‐toluenesulfonamide or N ‐benzylidenetoluenesulfonamide revealed that the reaction proceeds via a transfer hydrogenation mechanism and the whole process is micro‐reversible. Competitive reactions of benzyl alcohol and benzyl alcohol‐ d 7 with p ‐toluenesulfonamide revealed a kinetic isotope effect ( k H/ k D) of 3.287 (0.192) for the dehydrogenation of benzyl alcohol and 0.611 (0.033) for the hydrogenation of the N ‐benzylidene‐ p ‐toluenesulfonamide intermediate, which suggests that dehydrogenation of the alcohol is the rate‐determining step.