Polyene cyclization reactions are highly efficient and unique biomimetic transformations that yield complex polycyclic molecules from their acyclic precursors. The process involves a concerted step in the formation of stereo-controlled multiple C-C bonds. Over the years, various cation-mediated and radical-mediated synthetic methods have been developed to obtain highly enantioselective cyclization, along with the use of visible light in recent years. Such developments have significantly expanded the scope of terpene and polyene functionalization. However, all these strategies demand using expensive and toxic transition metal complexes or organic dyes as catalysts to accomplish the desired reaction. In contrast, here, we report a visible-light-mediated, catalyst-free cascade cyclization of geranyl phenols and farnesyl phenols containing bromo (-Br) and chloro (-Cl) groups at different positions of the phenolic ring. The desired cyclization product was obtained with high stereoselectivity using a blue LED light in hexafluoro-2-propanol without any photocatalyst.

Blue light-mediated catalyst-free polyene cyclization

ACS Spring 2022

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