A straightforward synthesis of functionalized 6<i>H</i>-benzo[<i>c</i>]chromenes from 3-alkenyl chromenes by intermolecular Diels–Alder/aromatization sequence
A new and metal-free approach to the synthesis of substituted 6H-benzo[c]chromenes has been developed. This three-step synthetic sequence starts from variously substituted salicylaldehydes and α,β-unsaturated carbonyl compounds to form the chromene core. The de novo ring-forming key step is based on a highly regioselective intermolecular Diels–Alder cycloaddition between 3-vinyl-2H-chromenes and methyl