Intramolecular hetero Diels–Alder reactions of vinyl allenes and aldehydes

Compounds containing a vinyl allene moiety linked to an aldehyde by a tether have been synthesised and shown to undergo the intramolecular hetero Diels–Alder reaction. Only one compound with stereochemistry consistent with an exo approach of the dienophile to the dienic portion of the vinyl allene was obtained in each case. Depending on the length of the tether and on the substitution pattern on the allene the reactions were spontaneous at room temperature or required heating or the presence of a Lewis acid to proceed.