Organocatalytic Enantioselective Formal (4 + 2)-Cycloadditions of Phosphine-Containing Dipoles with Isocyanates

Phosphine-catalyzed enantioselective formal (4 + 2)-cycloadditions of 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates with isocyanates have been developed for the first time. The initial SN2' attack of the chiral phosphine organocatalyst on 2-(4H-benzo[d][1,3]oxazin-4-yl)acrylates generated the key phosphine-containing dipolar intermediates, and the subsequent formal cycloaddition with isocyanates furnished a broad scope of 3,4-dihydroquinazolin-2-ones in 60-84% yields with 61-92% ee.