Photoreaction of conjugated polyacetylenes with some olefins

Abstract

1-Phenyl-1, 3-pentadiyne(PPD) was photolyzed in 2, 3-dimethyl-2-butene(DMB) to obtain a site specific [2+2] type 1:1 photoadduct 1. Irradiation of PPD with unsymmetrical olefins such as ethyl vinyl ether [EVE] and acrylonitrile[AN] yields site specific and regiospecific [2+2] type 1:1 photoadducts [$\underline{2}$ and $\underline{6}$] and 1:2 photoadducts[$\underline{3}$-$\underline{5}$ and $\underline{7}$-$\underline{9}$] which are bicyclo [2.2.0.] hexane derivatives having three stereoisomers. The 1:1 photoadducts are the primary photoproducts and 1:2 photoadducts are the secondary photoproducts because the 1:1 photoadducts are initially formed and prolonged irradiation of the solution results in the formation of 1:2 photoadducts. the regiochemistry of 1:1 photoadducts [$\underline{3}$-$\underline{5}$ and $\underline{7}$-$\underline{9}$] is determined by $^1H$-NMR spectrum and results of the regiochemistry of 1:2 photoadducts. The regiochemistry of 1:2 photoaddcuts is determined by mass spectral fragmentation patterns of thermally rearranged products of 1:2 adducts and NOE studies. The stereochemistry of 1:2 adducts is also identified by NOE studies. The formation pathway of these adducts is proposed. 1,4-Diphenyl-1, 3-butadiyne(DPB) was photolyaed in DMB to obtain three photoadducts($\underline{12}$-$\underline{14}$). the photoadducts $\underline{12}$ and $\underline{13}$ are initially formed and prolonged irrdiation of the solution results in decrease of $\underline{12}$ and formation fof $\underline{14}$ indicating that $\underline{14}$ is a secondary photoproduct of $\underline{12}$. At initial stage of photolysis of DPB with EVE yields a regiospecific [2+2] type photoadduct $\underline{15}$ as the primary photoproduct. Extended irradiation of the solution results in the formation of 1:2 photoadducts ($\underline{16}$ and $\underline{17}$). The secondary photoadduct(s) of $\underline{15}$ is (are) very unstable at room temperature and thermally rearranged...