ACTIVATED QUINONES - O-ADDITION VERSUS C-ADDITION OF PHENOLS - NEW REGIOSPECIFIC SYNTHESES OF XANTHONES, THIOXANTHONES AND N-METHYL-9-ACRIDONES

Activated quinones: O‐ versus C‐addition of phenols. New regiospecific syntheses of xanthones, thioxanthones and N‐methyl‐9‐acridones The acid catalyzed reaction of phenols with activated quinones, e.g. 2‐methoxycarbonyl‐1, 4‐benzoquinone or 2‐acetyl‐1, 4‐benzoquinone, leads to substituted biphenylderivatives (C, C‐addition) as has been previously described [1]. O, C‐Addition of phenols has now been achieved by using 2‐methoxypyridin or 4‐dimethyl‐aminopyridin [4] as basic catalysts. The resulting substituted diphenylethers can serve as convenient starting materials for regiospecific syntheses of substituted xanthones, especially for 1, 4‐dimethoxyxanthones. Arylthiols and N‐methyl‐N‐arylamines also react readily with activated quinones to give substituted di‐aryl‐thioethers and N‐methyl‐N, N‐diarylamines respectively; both types of compounds are convenient materials for regiospecific syntheses of substituted thioxanthones and N‐methyl‐9‐acridones. Copyright © 1979 Verlag GmbH & Co. KGaA, Weinheim