7-Hydroxy-2-および-3-phenylbenzo[b]thiophene類のFremy′s Saltによる酸化方向 : 3-Phenyl基の立体的影響 : 複素環キノン類の研究(第3報)

抄録

The structural confirmations of the migration product of phenyl group in benzo [b] thiophene derivatives from C₃ to C₂-position during the following reactions are shown. a) Cyclization of 2-(2, 5-dimethoxyphenylthio) acetophenone (X) with polyphosphoric acid. b) Demethylation of 7-methoxy-3-phenylbenzo [b] thiophene (IV) with anhydrous aluminium chloride. Oxidation of 7-hydroxy-3-phenylbenzo [b] thiophene (VI) with Fremy's salt gives 4, 7-dihydro-3-phenylbenzo [b] thiophene-4, 7-dione (VII), mp 103-104° (yield 35.3%), and 6, 7-dihydro-3-phenylbenzo [b] thiophene-6, 7-dione (VIII), mp 158-159° (yield 40.7%). On the other hand, the same reaction of 7-hydroxy-2-phenylbenzo [b] thiophene (XIV) yields 4, 7-dihydro-2-phenylbenzo [b] thiophene-4, 7-dione (XV), mp 174-175° (yield 31.5%), as a sole product. Examination of the oxidation products from the nine 7-hydroxyheterocyclic compounds with Fremy's salt (Table I) shows that the presence of a phenyl group at C₃-position is effective in producing o-quinone derivative. This phenomenon may be explained by the steric hindrance of a C₃-phenyl group to the formation of a key intermediate (XXb) which is the important step towards formation of p-quinone.