Reactions of Singlet Oxygen with Enol Esters

Article abstract of DOI:10.1021/jo00361a023

Singlet oxygenation of 1-adamantylideneethyl acetate (4) and 6,6-dimethylcyclohex-1-enyl acetate (7) produces only "ene" reaction products.Photooxygenation of Δ^1,6-2-oxabicyclo<4.4.0>decen-3-one (9), in contrast, yields ene, acyl-shifted, and <2+2> cycloaddition products.The product distribution resulting from oxidation of 9 indicates that attack of singlet oxygen (1O2) occurs exclusively on the same side of the double bond as the ester functional group.The bimolecular rate constant for reaction of 9 with 1O2 is found to be ca. 50 times larger than those of 4 and 7.These results are explained most economicaly by invoking the ini tial formation of a perepoxide intermediate.In the case of 9, stabilization of the transition state leading to the perepoxide by interaction of the incoming 1O2 molecule with the ester functionally produces the observed rate enhancement and stereospecificity.