Photochemical behaviour of 3,4-epoxy-3,4-dihydro-2H-1-benzopyrans, intermediates in the synthesis of pterocarpans, has been studied in various solvents. While ring contraction leading to 2,3-dihydrobenzofurans through a photodecarbonylation process was observed in cyclohexane, photoisomerisation leading to 3-chromanones was observed in acetone. This study has also been extended to antijuvenile hormone precocene(I) oxide. © 1992 Indian Academy of Sciences.