The temperature dependence of intramolecular [2+ 2] photocycloadditions has been studied for two series of cyclohexenones, α-and β-linked, respectively, to a variously substituted olefin moiety via a trimethylene chain. With one exception, the disappearance quantum yield of the starting material decreases sharply in a narrow temperature range to approximately one-half of its initial value. No such sharp temperature effect was observed on the product ...
