SYNTHESIS AND PHOTOREACTION OF 5-ALKENYLOXYPSORALEN DERIVATIVES

In order to investigate the intramolecular ''quenching'' of the photoe xcitation of some 5-alkenyloxypsoralen derivatives, we have prepared m odel compounds in which a psoralen moiety was linked at position 5 to a terminal double bond via a polymethylenic chain of various length (n = 2-9). The isolation and characterization of photo-cycloadducts obta ined for each compound after irradiation at 365 nn in a polar solvent was performed. The results on the photoreactivity of this series of co mpounds show that the 3,4-pyrone double bond of 5-alkoxypsoralens is t he most reactive. Four kinds of intramolecular photocycloadducts betwe en the 3,4-pyrone double bond and the chain unsaturation were obtained according to the length of the linking chain: cis-syn, hpns-syn, cis- anti and trans-anti. Their structures were established by a combinatio n of H-1 and C-13 NMR and fully assigned by H-1 NOE (nuclear Overhause r effect) and H-1-C-13 HMQC (heteronuclear multiquantum correlation) s pectroscopies. No traces of 4',5' adducts were detected.