InCl3 catalyzed domino route to 2H-chromene-2-ones via [4 + 2] annulation of 2-hydroxyarylaldehydes with α-oxoketene dithioacetal under solvent-free conditions

A facile and efficient synthesis of 3-aroyl/heteroaroyl/ferrocenoyl/alkanoyl-2H-chromen-2-ones has been developed by the cyclocondensation of α-oxoketene dithioacetals and 2-hydroxyarylaldehydes catalyzed by InCl3 under solvent-free conditions. No co-catalyst or activator is needed and MeSH is the only by-product of this protocol. The methodology involves ring annulation of 2-hydroxyarylaldehydes with a variety of α-oxoketene dithioacetals offering rapid entry into differentially substituted chromen-2-ones. The condensation of ferrocene derived α-oxoketene dithioacetal and 2-hydroxyarylaldehyde furnished coumarin installed on a ferrocene platform.