A remarkable photoreaction of 3-O-benzylhypericin

Irradiation of 3-O-benzylhypericin dissolved together with at least 1 equiv . of 'proton sponge' in benzene was shown, by means of UV/VIS, H-1-NMR, and mass spectrometric measurements, to produce the rearranged blepharismin-an alogous 11-phenyl-11H-benz[4,10]anthra[2,1,9,8-nopqa]pleiadene system. The latter compound yielded hypericin when treated with light and oxygen in ace tone solution, followed by aqueous NH4Cl. This reaction is considered to pr oceed via the oxybleopharismin-analog 3,4-benzal acetal of hypericin. The i mplications of the novel phototransformation for synthesis and biosynthesis of the natural products. as well as the structural peculiarities of the ph otoproducts, are discussed.