Formal [3+3] cycloaddition reaction of 4-hydroxythiocoumarin to 4Н-chromene-3-carbaldehydes: synthesis of thiochromeno[3',4':5,6]pyrano[2,3-b]chromen-6-ones

Abstract

A cascade reaction of 4-hydroxythiocoumarin and 4Н-chromene-3-carbaldehydes was developed, consisting of Knoevenagel condensation and oxa-6π electrocyclization in the presence of ammonium acetate as catalyst. A series of polycyclic acetals containing a fused thiocoumarin moiety were obtained