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

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- methoxyanthra-quinone, 4-hydroxy-1,5-dimethoxyanthraquinone, 1,4-dihydroxy-5-methoxyanthraquinone, and 2-hydroxy-2',4,4'- trimethoxybenzophenone.