The photochem. Wolff-rearrangement of title compds. I (X = CH2CHPhCH2, CH2CMe2CH2, CHPhCHPhCH2, OCMe2O, NRCONR; R = Me, Ph, cyclohexyl) at 120K-200nm gave ketoketenes II which on warning above 180K gave cyclopantanone and ketene dimers in some cases. Photolysis of I (X = NPhCONPh) in alc. at 300K-300nm gave valance isomer diazirine III. Photolysis of I (X = CH2CHPhCH2) in EtOH at 300K-200nm gave Et 4-phenylcyclopentan-2-onecarboxylate whereas photolysis of I (X = NPhCONPh) in MeOH at 300K-200nm gave Me 1,3-diphenylhydantoincarboxylate.