185-nm Photochemistry of Cyclobutene and Bicyclobutane

Article abstract of DOI:10.1021/ja00299a028

The high quantum yield of the direct 185-nm photolysis of cyclobutene (φ_s=0.71) leading to 1,3-butadiene is in accord with symmetry-allowed electrocyclic ring opening of a ?,?^*-excited singlet state of cyclobutene.The formation of ethene, acetylene, and methylenecyclopropane as minor products presumably involves cyclopropylmethylene and cyclobutylidene as carbene intermediates, formed on (?,3s)-Rydberg excitation of cyclobutene.The 185-nm photolysis of bicyclo<1.1.0>butane resembles that of the homologous bicycloalkanes.As main products cyclobutene (φ_p=0.30) and 1,3-butadiene (φ_p=0.29) are formed.On the other hand, the transformations of methylenecyclopropane on 185-nm irradiation, leading to ethene, acetylene, and 1,3-butadiene, are akin to radiolysis and gas-phase photolysis results of this substrate.