Asymmetric Organocatalysis of 4 + 3 Cycloaddition Reactions

Treatment of several 4-trialkylsilyloxypentadienals with a chiral secondary amine, trifluoroacetic acid, and a diene resulted in the formation of 4 + 3 cycloaddition products, which were enantiomerically enriched. This represents the first examples of the asymmetric organocatalysis of the 4 + 3 cycloaddition reaction. 2,5-Dimethylfuran reacted with 4-trimethylsilyloxy-2,4-pentadienal in the presence of catalytic amounts of chiral amine and acid to afford a cycloadduct in 64% yield as a single diastereomer with an enantiomeric excess of 89%.