Polybrominated methoxy- and hydroxynaphthalenes

Abstract

Regio- and stereoselective synthesis are described for convenient preparation of hydroxy- and methoxynaph-thalenes 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), andcis,cis,cis-2,3,5,8-tetrabromo-1,4-dimethoxy-1,2,3,4-tetrahydronaphthalene (8) were obtained with silver-induced substitution oftrans,cis,trans-1,2,3,4,5,8-hexabromo-1,2,3,4-tetrahydronaphthalene (3). Base-promoted aromatization of dimethoxides7and8afforded3,5,8-tribromo-1-methoxynaphthalene (9) and 2,5,8-tribromo-1-methoxynaphthalene (10). The reaction of6withsodium methoxide formed compounds10and 3,5,8-tribromonaphthalen-1-ol (16). Bromination of9and16withBr2in 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 compound10did not react in the same conditions. Pyridine-inducedelimination of hexabromide3afforded 1,4,6-tribromnaphthalene (21) in 99% yield and thermolysis of the hexabromide3gave mainly 1,4,6,7-tetrabromonaphthalene (22). Tetrabromide22was transformed to 1,4,6,7-tetramethoxynaphthalene(23) by copper-assisted nucleophilic substitution reaction.