Asymmetric Diels-Alder Reactions of 2-Pyrones with a Bifunctional Catalyst

Significance

An organocatalytic asymmetric ­Diels-Alder reaction of 3-hydroxy-2-pyrones with electron-deficient dienophiles has been developed. While bifunctional catalysts 1a or 1b were found to be effective for the Diels-Alder reactions with enone dienophiles, catalysts 2a or 2b were used with furanonitrile and maleonitrile dienophiles. In addition, the authors have shown catalyst-controlled exo/endo selectivity with α-chloroacrylonitrile as dienophile. With 5 mol% of catalyst 1 or 2 moderate to high yields (65-100%) and high enantioselectivities (er = 90:10 to 98:2) are obtained for different 2-pyrones and ­dienophiles.