Microwave-assisted synthesis and transformations of sterically hindered 3-(5-tetrazolyl)pyridines

Sterically hindered 2,4-disubstituted 3-(5-tetrazolyl)pyridines were synthesized from corresponding nicotinonitriles using microwave technology. 2-Methylnicotinonitriles were converted into the 2-azidomethyl-3-cyanopyridines via 2-hydroxymethyl and 2-chloromethyl derivatives. Intramolecular [3+2] cycloaddition of an heteroaromatic cyano group to side azido group was carried out to form a novel heterocyclic system containing a (tetrazolo)azaisoindole unit. Condensation of the 2-methylnicotinonitriles and aldehydes gave rise to the corresponding 2-vinyl derivatives, which were then transformed into novel heterocyclic system (5,6-dihydrotetrazolo[5,1-f]-1,6-naphthyridine) by intramolecular N-alkylation reaction of tetrazole ring with olefinic fragment. The 3-(5-tetrazolyl)pyridines obtained were alkylated to give the various N- and C-benzyl derivatives as well as acylated to afford the 3-(1,3,4-oxadiazol-2-yl)pyridines in good yields. A majority of above-mentioned reactions was carried out under microwave irradiation.