(L)-Proline catalysed efficient synthesis of 3-substituted 2,6-diarylpiperidin-4-ones

(L)-Proline catalyzed Mannich reaction of ketones, aromatic aldehydes and ammonia furnishes 3-substituted 2,6-diarylpiperidin-4-ones in enhanced yields (upto five times) compared to the reaction involving ketone, aldehyde and ammonium acetate. The catalytic efficiency of proline is ascribable to the involvement of an enamine intermediate that could result from the reaction of ketones with proline and the absence of the formation of bicyclic side product in this reaction.