Asymmetric N-H Insertion Reaction of alpha-Diazoesters and Carbamates Co-catalyzed by Dirhodium Acetate, Sufonic Acid and Chiral Sulfonamide Urea

The enantioselective N-H insertion of alpha-diazoesters and carbamates provides a potentially attractive approach to alpha-amino acid derivatives. Herein, a novel cooperative catalytic system of achiral dirhodium(II) acetates, chiral sulfonamide urea and achiral sulfonic acid was developed for asymmetric N-H insertion reactions. Prochiral ammonium ylide intermediates, generated in situ from alpha-diazoesters and carbamates initiated by dirhodium(II) acetate, underwent asymmetric protonation with a considerable enantioselectivity in the presence of chiral sulfonamide urea and achiral sulfonic acid as co-catalysts. The co-catalysts of chiral sulfonamide urea and achiral sulfonic acid were considered as a chiral proton shuttle assisting the asymmetric proton transfer process to control the enantioselectivity. This methodology provides an efficient and mild approach to a-amino acid derivatives in high yields (up to 84% yield) with moderate enantioselectivity (up to 77% ee).