Trapping of Hexadehydro-Diels–Alder Benzynes with Exocyclic, Conjugated Enals as a Route to Fused Spirocyclic Benzopyran Motifs

Exocyclic, conjugated enals react with benzynes generated by heating various triyne-containing substrates to produce spirocyclic benzopyran derivatives. These products are consistent with a mechanistic sequence that involves initial net [2+2] cycloaddition of the benzyne and aldehyde followed by 4π-electrocyclic ring opening and 6π ring closing.