s Photochemical Synthesis of Fused Five-membered O-heterocycles

Some transformations are not possible with ground-state reactions even in the presence of a catalyst, hence they are performed under photochemical conditions. Electron transfer occurs even with the photochemical excitement of one molecule where redox reaction is not possible at the ground state. The side products are obtained from ground-state reactions. For C-C bond formation during photochemical reactions, there is no requirement of any chemical activation of the substrates. Therefore, these reactions are presented here for the synthesis of fused five-membered O-heterocycles in the context of sustainable processes from 1964 to 2019.