Photolysis of 2,2-Diethoxy-2,3-dihydrophenalene-1,3-dione

Abstract

Irradiation of 2,2-diethoxy-2,3-dihydrophenalene-1,3-dione (6) with a pyrex-filtered high-pressure Hg arc lamp afforded acetaldehyde, 2-ethoxy-3-hydroxyphenalene-1-one (7) and bis-2-(2-ethoxy-l,3-dioxo-2,3-dihydro) phenalenyl (8). Mechanistic studies revealed that the first step of this photoreaction was a homolytic fission of the C–OC2H5 bond to 2-(2-ethoxy-1,3-dioxo-2,3-dihydro)phenalenyl radical (9) and ethoxyl radical. This homolytic fission occurred mostly from the triplet and in part from the singlet excited state of 6. Dimerization of 9 gave 8 and the disproportionation between 9 and ethoxyl radical gave acetaldehyde and 7. The photochemical behaviors of a variety of triketone derivatives were discussed.

The Chemistry of Vicinal Polycarbonyl Compounds

“…Investigation of the photochemistry (section VI.B) of vic-tetraketones 106 prompted study of the reactions of such tetraketones (2, Ar ) phenyl, p-tolyl, p-anisyl, mesityl, tert-butyl) with (benzoyloxy)phenyl ketene (163). This ketene was generated, in the presence of tetraketone, by reaction of triethylamine and the appropriate R-(aroyloxy)-R-arylcarboxylic acid chloride.…”

“…Otsuji et al 163 have reported an investigation of the photolysis of the diethylketal of phenalenetrione (17a) which proceeded via an R-cleavage mechanism. Differences in behavior between this compound and ninhydrin were discussed.…”

Chemistry of vicinal polyketones

“…The diethyl ketal of 42 showed similar behavior. 211 The one pinacol-forming reaction which may involve the usual H-atom abstraction type of mechanism is the irradiation203 of diethyl oxomalonate in cyclohexane to give diethyl tartronate ( 139) and Its pinacol. The fate of cyclohexane was not determined.…”