A series of endo-5norbornenyl ketones 1 was prepared which contained the following heterocyclic rings: 2-fury1, 2-thienyl, N-methyl-2-pyrryl, 3, 5-dimethyl-4-isoxaolyl, 5-methyl-3- isoxazolyl and 2, 5-dimethyl-4-oxazolyl groups. Oxetanes 2 were produced from the ketones either by direct irradiation (A> 300 nm) or by use of photosensitizers. The two isoxazolyl systems were irradiated at 254 nm and found to lead to additional products, two of which ...