Base hydrolysis of halolactones in the bicyclo(2.2.1)heptyl and bicyclo(2.2.2)octyl systems

The mechanism of ketocarboxylic acid formation in the base treatment of bicyclo[2.2.1]heptyl halolactones has been determined. On the basis of stoichiometry, kinetics, effect of leaving group, and isotopic labeling experiments, a dehydrohalogenation mechanism is proposed in which cleavage of the carbon-halogen bond precedes that of the carbon-hydrogen bond in the transition state. The relationship between El-like and syn-E2 transition states in these systems is discussed.In the bicyclo[2.2.2]octyl series base treatment of the halolactones yields oxidocarboxylic acids. The difference in behavior between the two systems is rationalized on the basis of molecular geometry.