A systematic study of photochemical behaviour of 3,4-epoxyprecocene-I and related epoxychromans was undertaken. Upon irradiation in acetone or cyclohexane, 3,4-epoxyprecocene-I 1 was found to undergo photoisomerisation to the corresponding 3-chromanone 2. In contrast, the photochemical behaviour of analogous 3,4-dihydro-3,4-epoxy-2H-1-benzopyrans 3 was found to be dependent upon the nature of solvent. Irradiation of 3 in cyclohexene led to photodecarbonylation leading to the formation of 2,3-dihydrobenzofurans 4, whereas irradiation in acetone resulted in the formation of chramanones 5. © 1989.