Study of an Unexpected Rearrangement of the α-Phenyl Pyrane Derivatives Prepared via Hetero-Diels−Alder Reaction of Acyclic Vinyl Allenes and Aldehydes

Abstract

The Lewis acid catalyzed hetero-Diels-Alder reaction between acyclic vinyl allenes and aldehydes as heterodienophiles was studied. This reaction allows for the preparation of pyrane derivatives in good yields, high facial and regioselectivity and moderate endo/exo ratio. When benzaldehyde was used as the heterodienophile, rearranged products were obtained depending on the reaction conditions. DFT calculations were used to study the rearrangement, concluding that it is a highly selective ionic process, driven by the stability of the rearranged products.