Photoisomerization of Linear 1,3-Dienes to Cyclopropane Derivatives

Mercury-photosensitized isomerizations of 2,3-dimethyl-1,3-butadiene, ttms-2,3-dimethyl-1,3-pentadiene, 4-methyl-1,3-pentadiene, fra/u-2-methyl-1,3-pentadiene, and 2,4-dimethyl-1,3-pentadiene have been investigated. With the exception of the last compound, which yielded no isomeric product, the others gave methyl-substituted cyclopropenes and, in the first two instances, methylenecyclopropanes as well. Quantum yields as a function of diene pressure and of added inert gas at constant diene pressure were obtained for 2,3-dimethyl-1,3-butadiene. Quantum yields as a function of added ethane were obtained for trans,-2,3-dimethyl-1,3-pentadiene. Mechanisms to explain these transformations are proposed. © 1971, American Chemical Society. All rights reserved.