Abstract
Alkoxy group effect at C2 position in 1,3-diradicals has attracted considerable attention from the substituent effect on the singlet-triplet energy gap and their chemical reactivity. In the present study, we have investigated the effect of the spiro-configured ethylene-acetal functionality. The ethylene-acetal functionality produces not only the lager singlet-triplet energy gap in 1,3-diradicals, but also the reactivity of the cyclopentane-1,3-diyls, when compared with the 2,2-dimethoxy substituted one.