Formal enantioselective [4+3] cycloaddition by a tandem Diels-Alder reaction/ring expansion

The tandem Diels-Alder reaction/ring expansion between cyclopentadiene and unsaturated aldehydes is a highly stereoselective process for the synthesis of bicyclo[3.2.1]octenones, the formal products of a [4 + 3] cycloaddition. When the initial cycloaddition was conducted in the presence of the chiral Lewis acid catalyst 14, the bicyclo[3.2.1]octenones were obtained in two steps in 72 - 85 % yields with up to 96 % ee and > 98 % de.