Vinyl-allenes as dienes in the Lewis acid-mediated hetero Diels–Alder reaction with aldehydes

The Lewis acid-mediated, hetero Diels–Alder reaction of a vinyl-allene system with aldehydes as heterodienophiles has been carried out. In the cases studied, only two cycloadducts have been obtained, which correspond to the endo (major compound) and exo (minor compound) approach of the aldehyde through the less hindered face of the dienic system.