Abstract
Abstract— In order to investigate the intramolecular “quenching” of the photoexcitation of some 5‐alkenyloxypsoralen derivatives, we have prepared model 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 photocycloadducts obtained for each compound after irradiation at 365 nm in a polar solvent was performed. The results on the photoreactivity of this series of compounds show that the 3,4‐pyrone double bond of 5‐alkoxypsoralens is the most reactive. Four kinds of intramolecular photocycloadducts between the 3,4‐pyrone double bond and the chain unsaturation were obtained according to the length of the linking chain: cis‐syn, trans‐syn, cis‐anti and trans‐anti. Their structures were established by a combination of 1H and 13C NMR and fully assigned by lH NOE (nuclear Overhauser effect) and 1H‐13C HMQC (heteronuclear multiquantum correlation) spectroscopies. No traces of 4′,5′ adducts were detected.
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