The photolysis of dione 3 (n= 4) in methylene chloride leads mainly to the isomeric, photolabile enol lactone 6. Diones 3 (n= 5, 6, or 7) on irradiation in methylene chloride solutions lead to 20, 50, and 40% yields of 4 (n= 5, 6, or 7), respectively. Pentamethyleneketene and hexamethyleneketene were also formed from diones 3 (n= 6 or 7). Little cycloelimination occurs in the case of dione 3 (n= 5). Small amounts of ...