Synthesis of the Benzotricyclo2,7>heptene Ring System via the Intramolecular -Cycloaddition Reaction of Some Cyclopropene Derivatives

Article abstract of DOI:10.1021/ja00351a051

The photo and thermal reactions of a number of 1,2-diphenyl-3-methyl-3-(o-vinylphenyl)-substituted cyclopropenes have been studied.The thermolysis of these systems gave substituted benzotricyclo<3.2.0.0^2,7> heptenes in good yield by means of a novel intramolecular <2+2> cycloaddition.The sensitized di-?-methane photorearrangement of several substituted benzonorbornenes was used to independently synthesize the thermal cycloadducts.The observed regiospecificity of the rearrangement is understandable in terms of formation of the most stable diradical intermediate.In contrast to the thermal results, the photosensitized irradiation afforded a mixture of two products.In addition to the <2+2> cycloadduct, a new compound was isolated whose formation involves attack of the ortho position of the triplet state on the terminal vinyl carbon followed by diradical coupling and subsequent rearomatization.Thermolysis or sensitized photolysis of several unsymmetrically substituted 1,3-diphenyl-2-methyl-2-(o-vinylphenyl)cyclopropenes afforded related cycloadducts.With these systems, the <2+2>-cycloaddition reaction is highly regiospecific and involves bonding from the cyclopropene carbon bearing the methyl group onto the terminal vinyl carbon.The silver ion and singlet excited-state behavior of several substituted cyclopropenes was also studied, and the results obtained were compared to the reactions which occur on thermolysis or sensitized photolysis.