Oxidative aromatization of some 1,4-dihydropyridine derivatives using NaBrO3

In this study, oxidation of some 3,5-diacyl or 3,5-diester 1,4-dihydropyridines to corresponding pyridine derivatives using sodium bromate in the presence of NH4Cl, NaHSO4 and Bu4NHSO4 under thermal conditions has been investigated. The yield and structure of formed products is similar under all conditions; however, the reaction is accelerated in the presence of Bu4NHSO4 and NaHSO4. In addition, oxidation of 3,5-diester 1,4-dihydropyridines, against 3,5-diacetyl 1,4-dihydropyridines using sodium bromate in the presence of tetrabutylammonium hydrogen sulfate leads to the corresponding pyridines in shorter reaction times than sodium hydrogen sulfate. The cheapness of reagent, high yielding, easy work up and mild condition make this method a useful addition to the available methods in organic synthesis.