合成路线1

The methylation of 3-cyanopyridine (I) with methyl iodide in acetone gives 3-cyano-1-methylpyridinium iodide (II), which is reduced with NaBH4 in methanol/water yielding 1-methyl-1,2,5,6-tetrahydropyridine-3-carbonitrile (III). The reaction of (III) with ethyl chloroformate and K2CO3 in 1,1,1-trichloroethane affords 3-cyano-1,2,5,6-tetrahydropyridine-1-carboxylic acid ethyl ester (IV), which is cyclized with sodium azide by means of AlCl3 in refluxing THF giving tetrazole (V). Alkylation of (V) with ethyl iodide and NaOH in refluxing acetone, followed by column chromatography, yields 3-(2-ethyltetrazol-5-yl)-1,2,5,6-tetrahydropyridine-1-carboxylic acid ethyl ester (VI). The decarboxylation of (VI) with HBr in acetic acid affords 2-ethyl-5-(1,2,5,6-tetrahydropyridin-3-yl)tetrazole (VII), which is methylated with formaldehyde/formic acid or with methyl iodide to give 2-ethyl-5-(1-methyl-1,2,5,6-tetrahydropyridin-3-yl)tetrazole (VIII). Finally, this compound is treated with L-(+)-tartaric acid.