A mixture of freshly distilled pyridine (A) and 1-chloro-2,4-dinitrobenzene (I) in dry acetone is allowed to reflux for 15 h. Removal of the solvent in vacuo affords a residue which is washed with ether, recrystallized in absolute ethanol and characterized as N-(2,4-dinitrophenyl)pyridinium chloride (II). To an ice-cooled solution of compound (II) in methanol, a suspension of isonicotinic acid hydrazide in methanol in five aliquots is added with stirring. Triethylamine is then added and the reaction is allowed to stand at room temperature overnight. The solid which precipitates is purified and characterized as compound (III). A suspension of compound (III) in dioxane:water (4:1 v/v) is heated under reflux for 12 h to afford a clear solution. Separation and purification of the products gives a yellowish crystalline solid of N-(4-pyridylcarbonylimino)pyridiniumylide (IV) and 2,4-dinitroaniline (V). A solution of compound (IV) in 95% ethanol is added dropwise to a solution of sodium borohydride in 95% ethanol pre-cooled to 0 C. After stirring for 4 h at 0 C, the reaction mixture is poured onto crushed ice and allowed to come to room temperature. Extraction with chloroform, drying and purification yields N-(4-pyridylcarbonylamino)-1,2,3,6-tetrahydropyridine.

A mixture of freshly distilled pyridine (A) and 1-chloro-2,4-dinitrobenzene (I) in dry acetone is allowed to reflux for 15 h. Removal of the solvent in vacuo affords a residue which is washed with ether, recrystallized in absolute ethanol and characterized as N-(2,4-dinitrophenyl)pyridinium chloride (II). To an ice-cooled solution of compound (II) in methanol, a suspension of isonicotinic acid hydrazide in methanol in five aliquots is added with stirring. Triethylamine is then added and the reaction is allowed to stand at room temperature overnight. The solid which precipitates is purified and characterized as compound (III). A suspension of compound (III) in dioxane:water (4:1 v/v) is heated under reflux for 12 h to afford a clear solution. Separation and purification of the products gives a yellowish crystalline solid of N-(4-pyridylcarbonylimino)pyridiniumylide (IV) and 2,4-dinitroaniline (V). A solution of compound (IV) in 95% ethanol is added dropwise to a solution of sodium borohydride in 95% ethanol pre-cooled to 0 C. After stirring for 4 h at 0 C, the reaction mixture is poured onto crushed ice and allowed to come to room temperature. Extraction with chloroform, drying and purification yields N-(4-pyridylcarbonylamino)-1,2,3,6-tetrahydropyridine.

A mixture of freshly distilled pyridine (A) and 1-chloro-2,4-dinitrobenzene (I) in dry acetone is allowed to reflux for 15 h. Removal of the solvent in vacuo affords a residue which is washed with ether, recrystallized in absolute ethanol and characterized as N-(2,4-dinitrophenyl)pyridinium chloride (II). To an ice-cooled solution of compound (II) in methanol, a suspension of isonicotinic acid hydrazide in methanol in five aliquots is added with stirring. Triethylamine is then added and the reaction is allowed to stand at room temperature overnight. The solid which precipitates is purified and characterized as compound (III). A suspension of compound (III) in dioxane:water (4:1 v/v) is heated under reflux for 12 h to afford a clear solution. Separation and purification of the products gives a yellowish crystalline solid of N-(4-pyridylcarbonylimino)pyridiniumylide (IV) and 2,4-dinitroaniline (V). A solution of compound (IV) in 95% ethanol is added dropwise to a solution of sodium borohydride in 95% ethanol pre-cooled to 0 C. After stirring for 4 h at 0 C, the reaction mixture is poured onto crushed ice and allowed to come to room temperature. Extraction with chloroform, drying and purification yields N-(4-pyridylcarbonylamino)-1,2,3,6-tetrahydropyridine.