Organocatalytic Asymmetry Aldol And Oxa-Diels-Alder Reaction

Enantioselective organocatalysis has recently provided a research avenue in which to explore the fundamental chemical parameters such as reactivity, selectivity and mechanism and in doing so has led to the discovery of many valuable reactions and catalysts. In this context, we document the organocatalytic asymmetric Aldol reactions as well as Oxa-Diels-Alder reactions.1. Readily tunable and bifunctional L-prolinamides as novel organocatalysts have been developed and their catalytic activities were evaluated in the direct asymmetric Aldol reactions of various aromatic aldehydes and tetrahydropyran-4-one. The reaction conditions have been optimalized. High isolated yields (up to 96%), enantioselectivities (up to >99% ee), and anti- diastereoselectivities (up to >99:1 dr) were obtained under the optimal conditions. All compounds were characterized by ¹H NMR, ¹³C NMR, and element analysis.2. Substituted di- and tetrahydropyran rings are frequently structural motifs in biologically active natural products. Herein, highly chemoselective synthesis of substituted tetrahydropyran-4-ones, via pyrrolidine catalyzed Oxa-Diels-Alder reaction ofα,β-unsaturated ketones with aldehydes, are described. This reaction provides six-membered oxygen-containing heterocycles in good yields. Moreover, we also studied organocatalytic asymmetric Oxa-Diels-Alder reactions of aldehydes withα,β-unsaturated ketones. The enantiomer excess of the product was up to 52%.