Selective dealkylation of methoxyanthraquinones via difluoro[1-hydroxymethoxyanthraquinonato-O1,O9]boron chelates: synthesis of hydroxymethoxyanthraquinones

Abstract

1,8-, 1,5-, 1,2-, and 1,4-Dimethoxyanthraquinones have been treated with boron trifluoride–diethyl ether to give difluoro (anthraquinonato) boron chelates (1a–d) respectively. 1,4,5-Trimethoxyanthraquinone was similarly converted separately in benzene and toluene into the mono-(2) and bis-difluoroboron (3)-chelates respectively, and 2,2′,4,4′-tetramethoxybenzophenone was converted by BF₃·Et₂O in toluene into the boron adduct (4). Treatment of these derivatives, (1a–d) and (2)–(4), with methanol gave the following uncomplexed derivatives in good yield respectively: 1-hydroxy-8-methoxyanthraquinone, 1-hydroxy-5-methoxyanthraquinone, 1-hydroxy-2-methoxyanthraquinone, 1-hydroxy-4-methoxyanthraquinone, 4-hydroxy-1,5-dimethoxyanthraquinone, 1,4-dihydroxy-5-methoxyanthraquinone, and 2-hydroxy-2′,4,4′-trimethoxybenzophenone.