Organocatalytic Regio- and Enantioselective (3+3)-Annulation of 2-(4H-Benzo[d][1,3]oxazin-4-yl)acrylates with 2,4-Dihydro-3H-pyrazol-3-ones

A chiral sulfonamide-phosphine catalyzed regio- and enantioselective (3 + 3)-annulation of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates with 2,4-dihydro-3H-pyrazol-3-ones has been established, affording a wide range of such 1,4,5,6-tetrahydropyrano [2,3-c]pyrazole-containing carboxylates in generally high yields (61–96%) with high diastereo- and enantioselectivities (8:1->20:1 dr, 85–95% ee). Based on several control experiments, a reaction mechanism was proposed. Importantly, the work represents the first example of using benzoxazinyl acrylates as three-atom synthons, which enriches the chemistry of benzoxazinyl acrylates.