Construction of Diverse and Functionalized 2H-Chromenes by Organocatalytic Multicomponent Reactions

A green and efficient one-pot process for the construction of diverse and functionalized 2H-chromenes was developed by using multicomponent reactions of salicylaldehydes, alkynes (i.e., propiolate and acetylenedicarboxylates), and alcohols. This new protocol was achieved by using L-proline as a mild and green organocatalyst and offers several advantages such as economic availability, low toxicity, ease of handling, high regioselectivity, and environmentally benign nature under mild reaction conditions. As an extension of this method, quinoline derivatives were synthesized by replacing salicylaldehyde with 2-aminobenzaldehyde, and the 2-hydroxy-2H-chromenes prepared by this approach were also successfully transformed into biologically interesting coumarins through an oxidation reaction.