Iminophosphorane-Catalyzed Enantioselective Ketimine Nitro-Mannich Reaction

Key words

nitro-Mannich reaction - iminophosphoranes - bifunctional catalysis

Significance

Dixon and co-workers report a new class of bifunctional Brønsted base/H-bond donor organocatalyst. The catalyst (bifunctional iminophosphorane, BIMP) can be applied to the ­ketimine nitro-Mannich reaction, generating β-nitroamines in good to excellent yields and ­enantioselectivities.

Comment

The authors developed a new catalyst motif consisting of a triaryliminophosphorane moiety as a Brønsted base and a thiourea moiety as an H-bond donor. The catalyst can be easily synthesized via Staudinger reaction of an organoazide and a triarylphospine. The efficiency of the catalyst was demonstrated by the application to the first catalytic enantioselective addition of nitromethane to ketone-derived imines under metal-free conditions. The reaction can be scaled up to multigrams and gives access to enantiomerically pure quaternary α-amino acids.