Reduction of 3,5-disubstituted pyridines to dihydropyridines

Abstract

The reduction of pyridine-3,5-dicarboxylates by sodium borohydride to give the corresponding 1,2- and 1,4-dihydropyridines has been investigated, and the compositions of the isomer mixtures produced in various solvents have been determined. New syntheses have been developed for 3,5-disubstituted 1,4-dihydropyridines involving reduction with sodium cyanoborohydride, and for 1,2-dihydropyridine-3,5-dicarboxylates involving reduction with diborane. Details of the previously reported catalytic hydrogenation of pyridines are given.