Haloalkane-driven dichotomous reactivity of aryl radicals as halogen and hydrogen atom transfer agents: photocatalytic olefin and alkyne functionalization cascades.

A visible-light mediated protocol for the annulative trifluoroethylation, perfluoroalkylation and di/tri-chloromethylation of olefins and alkynes tethered to aromatic rings is described. Both PIDA and diazonium salts can independently promote this transformation by simultaneously acting as both an oxidant and halogen atom transfer reagent. The reaction is applicable to multiple precursor classes, leading to the synthesis of various N- and O-containing ring systems including dihydroisoquinolinones, coumarins, fused benzimidazoles, and quinazolinone. The activation of chloroform and dichloromethane was also achieved by hydrogen atom transfer, displaying a mechanistic dichotomy of aryl radicals.