Abstract
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.
Highlights
Proline has emerged as an efficient and important enantioselective organocatalyst in several asymmetric transformations such as aldol reaction,[1] conjugate addition[2] involving ketones and aldehydes as nucleophilic component and additions to imines, nitroalkenes, crossed aldol reactions[3] involving different aldehydes as donors and acceptors, Mannich reaction[4] involving ketones, aldehydes and amines, etc
The finding that (L)-proline catalyzes asymmetric Mannich reaction[4,10] prompted us to examine whether the synthesis of 3substituted 2,6-diarylpiperidin-4-ones by the three-component reaction involving ketone, aromatic aldehyde and ammonia in the presence
This synthesis of piperidones was initially reported by Baliah and Noller[11] from ketone, aromatic aldehyde and ammonium acetate
Summary
Proline has emerged as an efficient and important enantioselective organocatalyst in several asymmetric transformations such as aldol reaction,[1] conjugate addition[2] involving ketones and aldehydes as nucleophilic component and additions to imines, nitroalkenes, crossed aldol reactions[3] involving different aldehydes as donors and acceptors, Mannich reaction[4] involving ketones, aldehydes and amines, etc. We have been interested in the study of synthesis, stereochemistry, biological activity and reactions of diversely substituted pipridin-4-one ring systems.[6,7,8,9] The finding that (L)-proline catalyzes asymmetric Mannich reaction[4,10] prompted us to examine whether the synthesis of 3substituted 2,6-diarylpiperidin-4-ones by the three-component reaction (which can be considered as a double Mannich reaction) involving ketone, aromatic aldehyde and ammonia in the presence No enantioselectivity has been found in the reaction with proline under the reaction conditions employed in the present study, it is of interest to note that the yields of the 3-substituted 2,6diarylpiperidin-4-ones formed are found to be significantly higher than those reported in the literature in the presence of ammonium acetate and the results are presented in this paper.
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