Visible-Light-Promoted Formal [4 + 3] Radical Annulation of Vinyldiazos: Access to Fluorinated Cyclohepta[b]indoles.

Abstract

Cyclohepta[b]indoles are important nitrogen-containing heterocycles, yet their efficient synthesis remains challenging. Herein, we report a visible-light-promoted formal [4 + 3] cyclization of 3-difluorobromoacetylindoles with vinyldiazos through a photoredox cascade radical process. This method provides straightforward access to a broad range of fluorinated dihydrocyclohepta[b]indole derivatives in good to excellent yields. The reaction features mild conditions, broad substrate scope, good functional-group tolerance, and operational simplicity. Gram-scale synthesis, product derivatizations, and late-stage modification of complex bioactive molecules further demonstrate the synthetic utility of this protocol.