Eco-friendly synthesis of fused pyrano[2,3-]pyrans ammonium acetate-mediated formal oxa-[3 + 3]cycloaddition of 4-chromene-3-carbaldehydes and cyclic 1,3-dicarbonyl compounds.

Various substituted polycyclic pyrano[2,3-]pyrans were synthesized the condensation of 4-chromene-3-carbaldehydes and their areno-condensed analogues with hetero- and carbocyclic 1,3-dicarbonyl compounds in acetic acid. Ammonium acetate was used as a green catalyst for the reaction. The process also involves the subsequent Knoevenagel condensation and 6π-electrocyclization of the 1-oxatriene intermediates formed.