Catalytic Asymmetric Construction of Halogenated Stereogenic Carbon Centers by Direct Vinylogous Mannich-Type...

A catalytic asymmetric vinylogous Mannich-type reaction of γ-halo-α,β-unsaturated N-acylpyrazoles and N-Boc-aldimines was disclosed, which afforded an array of halogenated (F-, Cl-, and Br-) allylic stereogenic carbon centers in high yields with good to high regio-, diastereo-, and enantioselectivities. The brominated product served as a suitable electrophile for common S_N2 nucleophilic substitution and copper-mediated S_N2' allylic alkylation with metal reagents. The utility of present methodology was demonstrated by the asymmetric synthesis of a common intermediate toward the synthesis of two chiral 2,3-disubstituted piperidine pharmaceuticals.