Acid-Catalyzed Regiodivergent Annulation of 4-Hydroxycoumarins with Isoprene: Entry to Pyranocoumarins and Pyranochromones

Abstract

An acid-catalyzed regiodivergent formal [3+3] annulation of 4-hydroxycoumarins with isoprene is developed. A variety of pyranocoumarins were obtained exclusively in the presence of strong Brønsted acid, while varying to Lewis acid delivered pyranochromones as main products. The protocol also features high atom-economy, wide substrate scope, easy scale-up, and good applications in natural product synthesis.