Aktivierte Chinone: O‐ versus C ‐Addition von Phenolen; eine neue, regiospezifische Synthese von Xanthonen, Thioxanthonen und N ‐Methyl‐9‐acridonen

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.