Stereochemical effects on the mechanism of the ozonolysis of (E)- and (Z)-o-(2-phenyl-3-methoxy-2-propenyl)benzophenone

The ozonolyses of (E)- and (Z)-o-(2-phenyl-3-methoxy-2-propenyl)benzophenone (6), which should proceed through a common carbonyl oxide intermediate 15, afforded distinctly different reaction product mixtures, suggesting that the substrate stereochemistry exerts an influence on the overall reaction mechanism: (a) The reaction of (E)-6 in carbon tetrachloride resulted in the formation of unidentified polymeric products, whereas 2,3-diphenylindene ozonide (8) was the major reaction product in acetic acid and methanol at 0 °C. From the ozonolysis of the isomeric keto olefin (Z)-6 in both the protic and aprotic solvents, however, the ozonide 8 was obtained almost quantitatively, (b) The reaction of (E)-6 in methanol-methylene chloride at -70 °C gave the methoxy hydroperoxide 9 in 81% yield, whereas the reaction of (Z)-6 under similar conditions led to the formation of the hemiperacetal 10 (14% yield) together with the ozonide 8 (49% yield). Moreover, the high degree of similarity in the nature and distribution of the products from the ozonolyses of keto olefin (Z)-6 and 2,3-diphenylindene (7) would be consistent with their respective reactions proceeding predominantly through a common carbonyl oxide intermediate.