The photolyses of the gamma-allenyl-substituted conjugated alkylidenec
ycloalkanones underwent the intramolecular oxa-Diels-Alder reaction an
d the E-Z geometrical isomerization, and for the cyclopentanone posses
sing a 3-methyl-1,2-butadienyl group, the intramolecular [2+2] cycload
dition also occurred. The oxa-Diels-Alder reaction takes place via pho
tochemical process of the Z-enones.