Structure and asymmetric diels-alder reactions of optically active allene-1,3-dicarboxylates

Optically active allene-1,3-dicarboxylates (1a and 2a), which contain the axial asymmetry of the allene moiety, were prepared. The Diels-Alder reaction of 1a and 2a with cyclopentadiene afforded the 1:1 (1a or 2a to cyclopentadiene) endo adducts 3a and 4a through the combination of the sterically favorable approach of the diene and the dienophile owing to the axial asymmetry of the allene moiety and the effective secondary orbital interaction. The absolute configurations of 3a and 4a were determined by chemical transformation and X-ray analysis. The absolute configuration of the axial asymmetry of 1a was also determined to be R by X-ray analysis.