Photosensitized Reactions of Cyclobutene in Solution

Irradiation of a solution of cyclobutene in acetone gives rise to tricyclo[4.2.0.02,5]octane, 5-methyl-4-hexenal, and cyclobutylacetone as the major products. Quantum yields for the formation of these products have been obtained at 2537 and 3130 A as a function of the concentration of cyclobutene. It is believed that 5-methyl-4-hexenal is formed through the addition of an excited acetone molecule to cyclobutene to give an oxetane which subsequently decomposes to this product. The irradiation of acetone and 1-methylcyclobutene gives 6-methyl-5-hepten-2-one in a similar fashion. Cyclobutylacetone is probably formed by a free-radical reaction that is photo-mitiated. The formation of all three of the products is quenched by the presence of even a trace of biacetyl. It is estimated that for every collision of a triplet acetone with a cyclobutene that gives an oxetane, there are 11 collisions which result in energy transfer to give a triplet cyclobutene. © 1966, American Chemical Society. All rights reserved.