Visible-Light-Induced Photoannulation of α‑Naphthyl Cyclopropane Carboxylic Esters to Functionalized Dihydrophenalenes

A general synthetic entry to functionalized dihydrophenalenes has been found using naphthyl-cyclopropane esters as starting materials. The desired annulation was possible with visible light, Ir­(Fppy)₃ as photocatalyst, BnNMe₂ or DABCO as electron donor, HAT-catalyst, and proton source. A broad scope of substituted naphthyl and azanaphthyl derivatives provided the photoannulation products in high yield. Deuteration studies support a photoredox mechanism involving the photoreductive cyclopropane opening to an enolate radical followed by an aryl radical trapping.