Photocyclisation of 3-alkoxy-6-chloro-2-(3-methylthiophen-2-yl)-4H-chromen-4-ones

Photochemical Transformation of some 3-benzyloxy-2-(benzo[b]thiophen-2-yl)-4Hchromen-4-ones: A Remote Substituent Effect

The effect on photochemical transformations of the substituents present remotely from the reaction site in 3-benzyloxy-2-(benzo[b]thiophen-2-yl)-4H-chromen-4-ones has been determined. The structure(s) of the substrates and photoproducts were established by spectroscopic techniques (UV, IR, and NMR). The substituents had profound effects on product yield and distribution. Electron withdrawing groups (EWGs) on the benzenoid moiety of the chromenone nucleus increased the yield of the photoproducts whereas electron donating groups (EDGs) decreased the yield. These results may be attributed to “state switching” of the substituents during excitation.