Catalyst-Controlled Inter- and Intramolecular Cascade [4 + 2] Annulations via Benzopyrylium Intermediates

We report two types of catalyst-controlled inter- and
intramolecular
cascade [4 + 2] annulations between diyne-carbonyls and alkenes, Pt­(II)-catalyzed
annulation with two alkenes via two benzopyrylium intermediates, and
Au­(I)-catalyzed annulation with one alkene via benzopyrylium and quinodimethane
intermediates. Additionally, Au­(I)-catalyzed reactions of highly nucleophilic
indole-yne-carbonyls with one alkene afford cascade [4 + 2] annulation
products in high yields through benzopyrylium and not quinodimethane
but carbocation intermediates, the contribution of which is supported
by DFT calculations.