Photochemistry of Cyclobutanes. I. Photolysis of Naphthalene peri-Fused Cyclobutanes in Rigid Media. Photocleavage from an Upper Triplet State

The photocleavage reaction of naphthalene perp-fused cyclobutanes (I–IV) in rigid media is found to proceed from one (or several) of the upper triplet states. Nearly planar cyclobutanes (I–III), which were photocleaved in fluid solutions to yield acenaphthylene and 1,2-ethylenedicarboxylic acid derivatives, afford 1,8-naphthalenediacrylic acid derivatives in addition to the above products by irradiation in rigid media. Twisted cyclobutane (IV), which is considerably stable to irradiation in fluid solutions, was also photocleaved in rigid media to give dimethyl 1,8-naphthalenediacrylate. An NMR study shows that the formation of these diacrylic acid derivatives from I–IV in rigid media is considerably stereospecific. The yield ratio of diacrylic acid derivatives to acenaphthylene formed in the photolysis of I–III is independent of the viscosity of the solvents, i.e., of the matrix rigidity, but depends on other properties of the rigid solvents. A concerted mechanism is proposed for the photocleavage reaction of I–IV in rigid media in order to explain the photochemistry different from that in fluid solutions.