The acetylation of naphthoquinones. The synthesis of 3-acetyl-5-methoxy- and 3-acetyl-5,7-dimethoxy-1,4-naphthoquinones

Abstract

The conversion of 5-methoxy- and 5,7-dimethoxy-1,4-naphthoquinones into their 3-acetyl derivatives is described. A key step is the Fries rearrangement of 1,5-dimethoxy-4-acetoxynaphthalenes to the corresponding 3-acetyl-4-naphthols with boron trifluoride–diethyl ether. Alternative Fries rearrangement of 1-acetoxy-4-hydroxy-5-methoxynaphthalenes gave the 3-acetylquinols, involving meta migration of the acetyl group. A convenient new synthesis of 2-acetyl-1,4-naphthoquinone is also reported.