Oxidation by singlet oxygen of 4,7-dimethoxy-2,9-di-t-butyloxepino[2,3-b]benzofuran, an oxidation product of the antioxidant BHA

Abstract

Tetraphenylporphin-sensitized photo-oxidation of 4,7-dimethoxy-2,9-di-t-butyloxepino[2,3-b]benzofuran (3) and reaction of the products with methanol cleaves the oxepine ring, producing the acetal (9) and its isomer (13), which may be derived respectively from the 1,4-endoperoxide and 1,2-dioxetane oxygen adducts of (3). The geometrical isomerization of (9) to (14), and the acidcatalysed hydrolysis of (9), (13) and (14) to the dihydrofuranylidenebenzofuranone (18) are described. Crystal structures were determined for compounds (9), (14), and (18).