Photomediated transformation of eremophilanes-I: Photooxidation of 2ß-angeloyloxy-10ß-H-furanoeremophilane

The photochemical oxygenation reaction of 2β-angeloyloxy-10β-H-furanoeremophilane (1), a sesquiterpene, was studied in benzene and methanol. Three photoproducts were isolated and characterized by IR 1 H-NMR, 13 C-NMR and mass spectral studies. Sesquiterpene itself was found to be singlet oxygen ( 1 O2) sensitizer. Addition of rose bengal increased the rate of photooxidation whereas as DABCO was found to decrease the rate of photolysis proving the involvement of 1 O2 in these photoreactions. 2β-Angeloyloxy-8-hydroxy–10β-Heremophilanolide (4) and 2β-angeloyloxy–7,8-epoxy-10β-H-eremophilanolide (6) were obtained as products in benzene. Photolysis in methanol gave a single product 2β-angeloyloxy-10β-H-8methoxy-12-hydroperoxy-dihydro-furanoeremophilane (7), which was further transformed into product 4, 8 and 12. Reaction was also carried out by adsorbing compound (1) on silica gel bound rose bengal, which yielded the products 4 and 6 with an increase in the rate of reaction.