Photoreaction of Acetylenic Compounds with Tetrahydrofuran

Abstract

Irradiation of phenylacetylene [1] in tetrahydrofuran in the presence of acetophenone or benzophenone using high pressure mercury lamp resulted in the formation of 1: 1 adducts β- (tetrahydro-2-furyl) -styrene [2 a and 2 b] and 1, 2-ethanediols. However, the reaction hardly tookplace in the presence of naphthalene or phenanthrene, or by nonsensitized irradiation with low pressure mercury lamp (Table 1). From the results, the reaction is considered to proceed via hydrogen abstraction by the excited keton sensitizers followed by addition of tetrahydrofuryl radical to [1].
In the photoreaction of methyl phenylpropiolate C 3 J with tetrahydrofuran, 1: 1 adducts, methyl a- (tetrahydro-2-fury1)-cinnamate (4 a and 4 b) were also obtained. The reaction was quenched by 1, 2-pentadiene and a\ Stern-Volmer plot (Fig.1) gave a straight line. The photoreaction of C 3 J and photoisotherization of the mixture of (4 a) and (4 b) were carried out by use of various triplet sensitizers (Table 2 and 3). From the results thus obtained, it was found that the triplet excited state of ( 3) has an impprtant role in the reaction, and the lowest triplet excitation energies of ( 3) and (4 b) (trans isomer) were estimated at 56.9-61.8 and approximately 59.5 kcal/mol, respectively.