Polybrominated methoxy- and hydroxynaphthalenes

Abstract

Regio- and stereoselective synthesis are described for convenient preparation of hydroxy- and methoxynaphthalenes starting from naphthalene (1). cis,cis,trans-2,3,5,8-Tetrabromo-4-methoxy-1,2,3,4-tetrahydronaphthalen-1-ol (6), cis,cis,trans-2,3,5,8-tetrabromo-1,4-dimethoxy-1,2,3,4-tetrahydronaphthalene (7), and cis,cis,cis-2,3,5,8-tetrabromo-1,4-dimethoxy-1,2,3,4-tetrahydronaphthalene (8) were obtained with silver-induced substitution of trans,cis,trans-1,2,3,4, 5,8-hexabromo-1,2,3,4-tetrahydronaphthalene (3). Base-promoted aromatization of dimethoxides 7 and 8 afforded 3,5,8-tribromo-1-methoxynaphthalene (9) and 2,5,8-tribromo-1-methoxynaphthalene (10). The reaction of 6 with sodium methoxide formed compounds 10 and 3,5,8-tribromonaphthalen-1-ol (16). Bromination of 9 and 16 with Br-2 in dichloromethane at room temperature produced 2,3,5,8-tetrabromo-1-methoxynaphthalene (14) and 2,3,4,5,8-pentabromonaphthalen-1-ol (18), respectively, while compound 10 did not react in the same conditions. Pyridine-induced elimination of hexabromide 3 afforded 1,4,6-tribromnaphthalene (21) in 99% yield and thermolysis of the hexabromide 3 gave mainly 1,4,6,7-tetrabromonaphthalene (22). Tetrabromide 22 was transformed to 1,4,6,7-tetramethoxynaphthalene (23) by copper-assisted nucleophilic substitution reaction.