The synthesis of chromenes, chromanes, coumarins and related heterocycles via tandem reactions of salicylic aldehydes or salicylic imines with α,β-unsaturated compounds

The tandem reactions of salicylic aldehydes or salicylic imines with alpha,beta-unsaturated compounds have only been studied systematically in recent years. These tandem reactions provide an easy access to a variety of heterocycles, such as chromanes, chromenes, coumarins and tetrahydroxanthenones, many of which are synthetic useful intermediates.