The benzo-3,4-coumarin scaffold is conspicous in the arena of secondary metabolites with a broad spectrum of bioactivities. Prominent examples include the antimalarial agent dioncolactone A, the antibacterials murayalactone and chrysomysin A, the antifungal alternariol and ellagic acid which shows antiproliferative and antioxidant properties. Predicated on the versatility and growing interest of this structural motif development of an efficient and sustainable entry into this privileged core is highly desirable. Herein, an operationally simple protocol is disclosed to facilitate entry to benzo-3,4-coumarins directly from biaryl-carboxylic acids without the need for substrate-pre-functionalization. Complementary to classic lactonization strategies, this disconnection relies on the oxidation competence of photo-activated (–)-riboflavin (vitamin B2) to generate the heterocyclic core via photo-induced single electron transfer (SET). Efficient generation of the aryl C(sp2)-O bond is contingent solely on molecular oxygen as the terminal oxidant. Collectively, the inexpensive nature of the catalyst (Sigma Aldrich, reagent grade 97%, A89200, 100g = $55.50), ease of execution and absence of external metal additives are a convincing endorsement for the incorporation of simple vitamins in contemporary catalysis.

Vitamin catalysis: Photocatalytic synthesis of benzocoumarins via (–)-riboflavin-mediated electron transfer

2019 Fall National Meeting

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