Synthesis of substituted Pyridines via Annulation of Ketones with Vinamidinium salts

For the past century, classical methods for the formation of pyridines have been used extensively. Such methods include the condensation of enaminoketones or β-ketoesters with 1,3-diketones[1]. The Hantzsch pyridine synthesis from β-dicarbonyl compounds in the presence of an aldehyde and ammonia,2 and the related Knoevenagel cyclization of β- aminoacrylates with β,α-unsaturated carbonyl compounds [3]. Despite the numerous studies and applications that have appeared in the literature [4]. Most methods are still severely limited in their use by the lack of generality, the harsh reaction conditions involved, the poor yields, or the formation of complex mixtures of side products. New methodologies alleviate some of these limitations. They include the inverse electron-demand Diels-Alder cycloaddition of triazines with electron-rich alkenes. The cycloaddition of azadienes with Fisher carbenesand the sequential reaction of metalated phosphonates with nitriles and unsaturated carbonyl compounds.