Enantio-complementary results

Discussion Taddol-catalyzed DA reactions provide simple and direct routes to functionalized cyclohexenones in enantiomerically enriched form. As with the HDA reactions, the best results were obtained when pure diene and dienophile were used, and the reaction temperature was rigorously maintained. Traces of moisture or acid impact negatively upon diene stability and product enantio-purities. One important advantage of the method is the commercial availability of both taddol catalyst 119 and the diene. The best substrates for the taddol-catalyzed DA reactions were a-substituted acroleins. This reactivity profile is complementary to that found for the secondary amine-based organocatalysis developed by MacMillan and co-workers, in which -substituted acroleins provided the best results [116]. 

A very recent study presented by Dujardin et al. describes the complementary use of chiral enol ethers as dienophiles in oxa Diels-Alder reactions. This approach has yielded promising results with regard to the synthesis of enantio-merically pure carbohydrates [481]. Further noteworthy studies directed to the preparation of biologically active amino sugars from enaminoketones have been carried out in our group [110]. 

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