Visible-Light-Promoted 6π Photocyclization of ortho-Biaryl-Appended β-Ketoesters

A photocatalyst- and additive-free visible-light-induced6 pi-photocyclizationof ortho-biaryl-appended beta-ketoesters has beendeveloped. Upon irradiation with visible light, substrates undergo6-endo-trig cyclization/1,5-H shift to 9,10-dihydrophenanthren-9-olswith high efficiency and selectivity. The reaction proceeds via conrotatory ring closure followed by a suprafacial 1,5-hydrogenshift leading to the observed single trans-fusedproducts. Preliminary mechanistic studies reveal the feasibility ofboth 1,5-H shift and intersystem crossing of the diradical intermediate.

Automated summary

A photocatalyst- and additive-free visible-light-induced 6 pi-photocyclization of ortho-biaryl-appended beta-ketoesters has been developed, which allows the efficient and selective formation of trans-fused products. Preliminary mechanistic studies indicate the feasibility of both 1,5-H shift and intersystem crossing of the diradical intermediate.