Photoreaction of 1-phenyl-1, 3, 5-heptatriyne with unsaturated fatty acid methyl ester

Abstract

Some conjugated polyacetylenes were prepared sucessfully with moderate yields by proper coupling methods from comercially available cheap starting material. 1-Phenyl-1,3,5-heptatriyne (7``) was prepared by the use of 1-trumethylsilyl-1,3-pentadiyne which is a very stable precusor for 1,3-pentadiyne at room temperature. 1-Methoxy-4-phenylbut-1-en-3-yne (8``) was durectly introduced by using the phenyliodide and $PdCl_2(PPh_3)_2$ as a catalyst. 1-Phenyl-1,3-pentadiyne (9``) and 1-phenyl-4-trimethylsilyl-1,3-butadiyne (10``) were easily prepared from 8``. Trimethylsilyl group contributes to the stability of the diyne unit. 1,6-Diphenyl-1,3,5-hexatriyne (12``) was synthesized by Cadiot-Chodkiewiez coupling reaction. The near-UV induced photoreactions of 1-phenyl-1,3,5-heptatriyne (PHT) with undecylenic(10-undecenoic) acid methyl ester(UAME) has been investigated in n-hexane as a model reaction for PHT phototoxic action via the viral membrane damage. The photoreaction of PHT with 1-hexene has been investigated as a reference reaction. Four major photoadducts (1-4, 5-8) have been isolated in both cases and purified by normal and reverse phase liquid chromatography. The structures of these adducts were determined by mass, UV absorption, FT-IR, $^1H$ and $^{13}C$ NMR spectral analyses, one-and two-dimensional nuclear Overhauser effect (1D NOE and NOESY) studies, and $^1H-^1H$ homo correlation spectroscopy (COSY). All the data indicate that the adducts are cyclobutenes resulting from the [2+2] photocycloaddition of PHT to UAME and 1-hexene. The site of inital bond formation may be the $C_1$, $C_3$, $C_4$, and $C_6$carbons of PHT with the 11 position of the fatty ester. These reactions most likely result in the formation of cumulene type diradical spections. Irradiation of PHT with linoleic acid methyl ester (LANE) in deaerated solution of n-hexane at 350 nm yields six 1:1 photoadducts (9-14) as major products. The regiochemistry of these adducts were determined by $^{13...