Kinetics of the Photochemical Dimerization of Olefins to Cyclobutane Derivatives. I. Intramolecular Addition

Abstract

The photoisomerization reaction (2), has been studied in six 1, 3-dienes and in 1, 3, 5-cycloheptatriene. It was observed that 1, 3-pentadiene, isoprene and 2, 3-dimethvl-1, 3-butadiene gave rise to 3-methyl-, 1-methyl- and 1, 2-dimethylcyclobutene, respectively, while 1, 3-cycloöctadiene and 1, 3, 5-cycloheptatriene yielded the previously reported cyclobutane derivatives. The formation of 1, 2-dimethylcyclobutene from 2, 3-dimethyl-1, 3-butadiene in the vapor phase was studied in the presence of oxygen, nitric oxide and ether. The reaction is believed to be intramolecular and to, originate in the singlet state of the molecule. The quantum yields for the photoisomerization reaction in solution at 2537 Å. fell in decreasing order as: 1, 3-cycloöctadiene > 2, 3-dimethyl-1, 3-butadiene > isoprene > 1, 3-pentadiene = 1, 3, 5-cycloheptatriene. Under the same conditions, the formation of a cyclobutene product from 1-methoxy-1, 3-butadiene and 2, 4-dimethyl-1, 3-pentadiene could not be detected. Rate studies on the irradiation of a mixture of cis- and trans-1, 3-pentadiene in solution indicated that the trans compound was the sole source of 3-methylcyelobutene, and that this reaction was faster than the photoisomerization of trans- to cis-pentadiene. © 1962, American Chemical Society. All rights reserved.