A general protocol for radical anion [3 + 2] cycloaddition enabled by tandem Lewis acid photoredox catalysis.

We report herein a method for intermolecular [3 + 2] cycloaddition between aryl cyclopropyl ketones and alkenes involving the combination of Lewis acid and photoredox catalysis. In contrast to other more common methods for [3 + 2] cycloaddition, these conditions operate using a broad range of both electron-rich and electron-deficient reaction partners. The critical factors predicting the success of these reactions is the redox potential of the cyclopropyl ketone and the ability of the alkene to stabilize a key radical intermediate.