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Copper-Catalyzed N-Alkylation of Sulfonamides with Benzylic Alcohols: Catalysis and Mechanistic Studies
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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 sulfon-ACHTUNGTRENUNGamides 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-d7 with p-toluenesulfonamide, Nbenzyl-p-toluenesulfonamide or N-benzylidenetolu-ACHTUNGTRENUNGenesulfonamide 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-d7 with ptoluenesulfonamide revealed a kinetic isotope effect (kH/kD) of 3.287 (0.192) for the dehydrogenation of benzyl alcohol and 0.611 (0.033) for the hydrogenation of the N-benzylidene-p-toluACHTUNGTRENUNGenesulfonamide intermediate, which suggests that dehydrogenation of the alcohol is the rate-determining step.

Keywords: alcohols; alkylation; CN bond formation; copper catalysts; sulfonamides

★★★☆☆ Cui XJ,Shi F,Man Kin Tes,et al. Copper-catalyzed N-alkylation Of Sulfonamides With Benzylic Alcohols: Catalysis And Mechanistic Studies[J]. Adv. Synth. Catal.,2009,351:2949-2958.