Photocatalytic 1,6-HAT-Enabled Formal [3 + 3] Annulation of Vinyl Azides with α-Bromomalonates to Tetrahydropyridines.

A visible-light-induced formal [3 + 3] annulation of vinyl azides with branched alkyl-substituted α-bromomalonates is reported for the synthesis of polysubstituted 2,3,4,5-tetrahydropyridines. Photocatalytic generation of a carbon-centered radical, followed by addition to the vinyl azide and N2 extrusion, affords an iminyl radical that undergoes 1,6-HAT and cyclization. The reaction proceeds under mild conditions, exhibits broad substrate compatibility, and is amenable to gram-scale synthesis. Hydrogenation of the products provides highly substituted piperidines, demonstrating the synthetic utility of the method.