Photoaddition of Tertiary Amines to 2‐Cyclopentylidenecyclopentanone

Abstract Photochemical reactions of 2‐cyclopentylidenecyclopentanone with diisopropylmethylamine, diisopropylethylamine, dimethylaniline, triethylamine, isopropyldimethylamine and dimethylbutylamine in acetonitrile were studied. Besides the addition product, a novel 3+2 cycloaddition adduct 3a‐hydroxytrispiro(octahydropentalene‐1,1′:2,1″:3,1‴‐triscyclopentane)‐2‴‐one was isolated. The quantum yield and Stern‐Volmer parameters with triplet quencher piperylene are reported. From these kinetic studies of mechanism photo‐induced electron transfer and proton transfer is proposed for formation of the novel 3+2 cycloadduct of 2‐cyclopentylidenecyclopentanone.