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

Wang, T.; Oswood, C. J.; Hoye, T. R. Syn. Lett. 2017, 28, A-C. 

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.