Oxidation of 7-hydroxy-2, 3-diphenylbenzofuran (III) with Fremy's salt, [ON (SO
3K)
2], gives 4, 7-dihydro-2, 3-diphenylbenzofuran-4, 7-dione (IX), mp 240-241°, (yield 40%) and 6, 7-dihydro-2, 3-diphenylbenzofuran-6, 7-dione (X), mp 160-161°, (yield >40%). Oxidation of 7-hydroxy-2, 3-diphenylbenzo [b] thiophene (IV) with the same reagent affords 4, 7-dihydro-2, 3-diphenylbenzo [b] thiophene-4, 7-dione (XXII), mp 162-163°, (yield 14.2%) and 6, 7-dihydro-2, 3-diphenylbenzo [b] thiophene-6, 7-dione (XXIII), mp 202-203.5°, (yield 45.5%).
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