The irradiation of methyl geranate (3) in ether using 254 nm lamps produces methyl 5- methyl-2-isopropenyl-4-hexenoate (13), 1, 6, 6-trimethyl-endo-5-carbomethoxybicyclo-[2.1. 1] hexane (11), methyl 2-isopropenyl-5-methylcyclopentanecarboxylate (12) and methyl (3Z)- 3, 7-dimethyl-3, 6-octadlenoate (14). Photolysis run in water or in ether in the presence of base generates two additional dienes: methyl 3-methylene-7-methyl-6-octenoate (16) and ...