Regiospecific Electrophilic Substitution of Aminopyridines: Ortho Lithiation of 2-, 3-, and 4-(Pivaloylamino)pyridines

Article abstract of DOI:10.1021/jo00168a007

2- and 4-(pivaloylamino)pyridines have been shown to undergo metalation exclusively at C-3 and these smoothly react with a variety of electrophiles to produce 2,3- and 3,4-disubstituted pyridines, respectively.Removal of the pivaloyl protecting group results in overall electrophilic substitution of an aminopyridine.Utilization of this method is exemplified by efficient syntheses of 2- and 4-aminonicotinaldehydes.Minor modifications of the reaction conditions permitted exclusive ortho metalation of 2-(pivaloylamino)pyridines additionally functionalized by chloro, fluoro, or methyl groups.Although the major product from reaction of 3-(pivaloylamino)pyridine by this method was metalation at C-4, the reaction was complicated by substantial quantities of product derived from nucleophilic attack by n-butyllithium on the pyridine nucleus.