Abstract: We have studied the intramolecular photochemistry of dienones lOa, b-l2a, b. The initial rate of loss of alkene stereochemistry in recovered starting ketone provides a measure of the rate of reversion (k,) of the biradical intermediate (Scheme I) relative to its conversion to products (kp). Results are presented in Table I along with quantum yields for products (ap) and for reversion (ar) and the fraction of absorbed light not accounted for by these ...