The Natural Product Esculetin as an Efficient Photoacid for the Visible-Light-Mediated Acetalization/Ketalization Reaction.

The development of photochemical protocols for the production of fine chemicals and industrially interesting products, employing sustainable catalysts under mild conditions, is of high interest. We demonstrate herein that esculetin, a naturally occurring coumarin widespread in plants, is an efficient photoacid, catalyzing acetalization/ketalization reactions under visible light irradiation. A variety of aldehydes and alcohols produce acetals in high yields, using a low catalyst loading of esculetin under 427-nm LED irradiation. In addition, various ketals, including industrially interesting products, such as solketal, fructone, and levulinate-based ketals, are generated in high yields. Esculetin has been proven to be an excellent, efficient photocatalyst for the production of acetals and ketals under mild and environmentally friendly conditions, highlighting that natural products offer a platform for investigation in an effort to discover sustainable renewable photocatalysts.