Photochemical domino reaction driven C-H/S-H functionalization of bioactive molecules to access xanthene scaffolds

A visible-light-induced C(sp²)-H functionalization of indoles by using Schreiner's thiourea as the organocatalyst has been reported. With the aid of a three-component domino reaction between 2-hydroxybenzaldehydes, cyclic-1,3-diketones, and a variety of indoles, the corresponding densely functionalized xanthene scaffolds were isolated in good to excellent yields. Apart from these, a broad range of other bioactive natural products including kojic acid, lawsone, and 4-hydroxycoumarin were also investigated instead of indoles for the present work. All the molecules participated in the photochemical reaction smoothly and provided the desired xanthenes in synthetically valuable yields. Therefore, the present energy-efficient catalytic strategy was also very successful in executing challenging carbon-sulfur bond formation reactions, demonstrating the synthetic potentiality of the work. Notably, this air-stable, transition metal-free approach with broad functional group tolerability provides an alternative to conventional methods.