Use of dissolving metals in the partial reduction of pyridines: formation of 2-alkyl-1,2-dihydropyridines

The partial reduction of a series of electron deficient pyridines to give both 1,2- and 2,5-dihydropyridines is described. The factors that lead to formation of such dihydropyridines are discussed and it was found that, generally, the presence of two activating groups on the pyridine nucleus is optimal. A series of 2-alkyl-1,2-dihydropyridines was prepared using either Birch or sodium naphthalenide reducing conditions and some preliminary derivatisation chemistry has been examined. The identity of three relevant nitrogen containing heterocycles was proven by X-ray crystallography.