Photoredox-enabled ring-opening of cyclobutanes via the formation of a carbon radical†

Abstract

The high strain energy of cyclobutanes has been utilized for selective ring-opening, enabling the synthesis of valuable linear aliphatic compounds. Although significant progress has been observed recently, most of the approaches appear to be limited to two major manifolds, namely, transition metal-catalyzed carbon–carbon (C–C) oxidative addition or cyclobutyloxy radical-initiated ring opening. In sharp contrast, we describe photoinduced C–C activation using a cyclobutylcarbinyl radical to access γ,δ-unsaturated ketones obtained from cyclobutyl tertiary alcohols and sulfonyl chlorides through a strain release strategy associated with the formation of a stabilized radical. Furthermore, the ketocarbonyl group also enables diverse post-synthetic modifications. Overall, our approach is characterized by broad functional group tolerance, ample substrate scope, and scalability. Our findings represent an alternative method to the aforementioned methods for remote 1,4-difunctionalizations, accompanied by a synthetically useful C–C double bond persisting in the obtained products.