Photochemical and thermal transformations of 7-silabicyclo[2.2.1]Heptadiene and 7-silabicyclo[2.2.1]heptene systems

Abstract

2,3-Dicarbomethoxy-7,7-dimethyl-7-silabicyclo[2.2.1]hepta-2,5-diene (III) on photolysis gave dimethyl tetraphenylphthalate whereas the photolysis of 7,7-dimethyl-7-silabicyclo[2.2.1]hep-5-ene-2,3-dicarboxylic anhydride (XIa) resulted in the formation of 1,1-dimethyl-2,3,4,5-tetraphenyl-1-silacyclopentadiene (XIIIa). The thermolysis of XIa also gave rise to XIIIa. Similarly, the photolysis as well as thermolysis of 1,4,5,6,7,7-hexaphenyl-7-silabicyclo[2.2.1]hept-5-ene-2,3-dicarboxylic anhydride (XIb) led to hexaphenylsilacyclopentadiene (XIIIb). Attempts to detect radical intermediates in these thermal and photochemical transformations by carrying out the reaction in the presence of hydroquinone, hydrazobenzene, 3,6-diphenyl-1,2-dihydro-1,2,4,5-tetrazine, cumene and tolan were unsuccessful. An attempted preparation of 7-silabicyclo[2.2.1]hepta2,5-dienes by the reaction of silacyclopentadienes such as 1-methyl-1-vinyl2,3,4,5-tetraphenyl-1-silacyclopentadiene (XV) and 1-methyl-1,2,3,4,5-pentaphenyl-1-silacyclopentadiene (XVI) with dimethyl acetylenedicarboxylate resulted in the isolation of dimethyl tetraphenylphthalate indicating that the corresponding 7-silabicyclo[2.2.1]hepta-2,5-dienes are thermally unstable.