New syntheses of substituted pyridines via bromine-magnesium exchange

Bromine-magnesium exchange using iPrMgCl in THF at room temperature on 2-, 3- and 4-bromopyridines allowed the synthesis of various functionalized pyr idines. The methodology was successfully used for the synthesis of 4-azaxan thone. Moreover, single exchange reactions observed on 2,6-, 3,5-, 2,3- and 2,5-dibromopyridines, with complete regioselectivity in the case of 2,3- a nd 2,5-dibromopyridines, afforded substituted bromopyridines, which were th en involved in a second exchange step to provide difunctionalized pyridines . (C) 2000 Elsevier Science Ltd. All rights reserved.