Selective bromination of 1-bromonaphthalene: efficient synthesis of bromonaphthalene derivatives

Selective and specific preparation methods are described for 1,4-dibromonaphthalene, 1,5-dibromonaphthalene and 1,3,5-tribromonaphthalene. The reaction of 1-bromonaphthalene and naphthalene with stoichometric quantities of bromine by using a minimum amount of solvent (methylene chloride) at −30 and −50°C smoothly affords 1,4-dibromonaphthalene in 90% yield. Photobromination of 1-bromonaphthalene in CCl4 at −30°C gives 1,2,3,4,5-pentabromo-1,2,3,4-tetrahydronaphthalenes, whereas 1,5-dibromonaphthalene is obtained at reflux (77°C) in 80% yield under the same conditions. Dehydrobromination of the pentabromide by t-BuOK affords 1,3,5-tribromonaphthalene as a sole product (91%). 1,5-Dibromo- and 1,3,5-tribromonaphthalenes were efficiently converted to the corresponding methoxy naphthalene derivatives.