Synthesis and catalytic activities of (S)-1-formylpyrrolidine-2-carboxylic acid derivatives for the enantioselective reductions of both a ketone and a ketimine

A series of (S)-1-formylpyrrolidine-2-carboxylic acid derivatives (6a-t) have been synthesised and examined as chiral organocatalysts in the asymmetric reduction of both ketone 2 and ketimine 3. These organic activators afforded good to moderate enantioselectivities in the asymmetric reductions of both the ketone and the ketimine. Among them, organic activator 6h displayed the best efficiency, affording a 84% yield and 41% ee in the reduction of the ketone and 75% yield and 52% ee in the reduction of the ketimine.