Palladium-catalyzed [2 + 2 + 1] annulation: access to chromone fused cyclopentanones with cyclopropenone as the CO source

Abstract

Herein we report a palladium-catalyzed [2 + 2 + 1] annulation among 3-iodochromones, bridged olefins, and cyclopropenone, giving a variety of chromone fused cyclopentanones that are of interest in medicinal chemistry. This protocol involves a Heck coupling/C(sp²)–H activation/carbonylation sequence, forming two C(sp²)–C(sp³) bonds and a C(sp²)–C(sp²) bond as well as a cyclopentanone unit in a single operation. Importantly, cyclopropenone in this methodology was utilized for the first time as the sole CO surrogate in the carbonylation process; its exceptional potential in carbonylation will be an inspiration for organic chemists.