The development of knoevenagel-michael cyclocondensation through a single-electron transfer (SET)/energy transfer (EnT) pathway in the use of methylene blue (MB+) as a photo-redox catalyst

Abstract

Through the Knoevenagel-Michael cyclocondensation of malononitrile, aryl aldehydes, and resorcinol, a multicomponent green tandem method for the metal-free synthesis of 2-amino-4H-chromene scaffolds was developed. At room temperature in an aqueous solvent, photo-excited state functions formed from methylene blue (MB+) were used as single-electron transfer (SET) and energy transfer (EnT) catalysts using visible light as a renewable energy source in the air atmosphere. This research looks toward expanding the use of a non-metal cationic dye that is both affordable and readily available. Methylene blue is catalyzed by photochemical means using the least amount of catalyst, which results in excellent yields, energy efficiency, environmental friendliness, high atom economy, time-saving features, and ease of operation. As a result, various ecological and sustainable chemical properties are met. Surprisingly, such cyclization may be carried out on a gram scale, indicating the reaction's potential industrial application.