The irradiations of 5-alkyl-1-hydroxy-8-oxabicyclo[3.2.1]octa-3,6-dien-2-ones, either in benzene or methanol by means of a high-pressure mercury lamp produced 2-alkyl-3-oxatricyclo[3.3.0.02,8]octane-4,6-diones. Although the intermediate ketenes could be detected by low temperature NMR, no adduct was formed in protic solvents.
Anodic oxidation of 2,7- and 2,3-dimethoxytropones gave the correspondong isomeric o-tropoquinone bisacetals, 2,2,7,7-tetramethoxycyclohepta-3,5-dienone and 2,2,3,3-tetramethoxycyclohepta-4,6-dienone in good yields. By H2SO4-treatment in AcOH–Ac2O, former afforded 4-acetoxy-2,7-dimethoxytropone, 2,5-diacetoxy-7-methoxytropone and 4,5-diacetoxy-3-methoxytropone, latter did no such product. Similar oxidation of 2-bromo-7-methoxytropone gave alternative p-tropoquinone bisacetal derivatives.
In connection with the study of the photorearrangement of bicyclic dienones and trienones via ketene intermediates the photorearrangement of the dienones (I) is investigated.
The dimethoxytropones (I) or (VIII) are electrochemically oxidized in the presence of methanol (II) to give the tetramethoxy compounds (III) and (IX) and the dimer (X).
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