Ascorbic acid: an efficient organocatalyst for environmentally benign synthesis of indole-substituted 4H-chromenes

An expedient, straightforward, and efficient one-pot three-component synthesis of biologically relevant indole-substituted 4H-chromenes has been developed by the reaction of various indoles, malononitrile, and salicylaldehydes using a catalytic amount of ascorbic acid in aqueous ethanol at room temperature. The significant features of the developed protocol are the clean reaction profile, operational simplicity, non-hazardous experimental conditions, no column chromatographic purification, use of an inexpensive, commercially available, and non-toxic metal-free catalyst, accomplishment of good to excellent yields, and large-scale synthesis.