Vitamin Catalysis: Direct, Photocatalytic Synthesis of Benzocoumarins via (−)-Riboflavin-Mediated Electron Transfer

An operationally simple protocol is disclosed to facilitate entry to benzo-3,4-coumarins directly from biaryl carboxylic acids without the need for substrate prefunctionalization. Complementary to classic lactonization strategies, this disconnection relies on the oxidation competence of photoactivated (−)-riboflavin (vitamin B 2 ) to generate the heterocyclic core via photoinduced single electron transfer. Collectively, the inexpensive nature of the catalyst, ease of execution, and absence of external metal additives are a convincing endorsement for the incorporation of simple vitamins in contemporary catalysis.