Ion-pairing catalysis in the enantioselective addition of hydrazones to N-acyldihydropyrrole derivatives

We have demonstrated that dihydropyrrole-based enamide derivatives can act as efficient precursors of chiral quaternary N-acyliminium salts under BrOnsted acid catalysis that undergo reactions with hydrazones, the latter participating as masked nucleophilic carbonyl group equivalents. The optimized methodology provides a variety of enantiopure -substituted proline derivatives in excellent yields, being even compatible with disubstituted -enamides that generate two contiguous stereocentres.