N-acyl and N-alkoxycarbonyl derivatives of 1H-1,2,3-triazolo-[4,5-c] pyridine; preparation and application

Article abstract of DOI:10.1002/jhet.5570430223

The N-acylating and N-alkoxycarbonylation ability of the N-substituted 1,2,3-triazolo[4,5-c]pyridines 1a-e have been investigated. The alkoxycarbonyl triazolopyridine derivatives (1c-e) were readily prepared in 81-96% yield (the corresponding tetrafluoroborate > 95%). Triazolo[4,5-c]pyridine (1) has been shown to work as a good leaving group by the formation of amido- and carbamate protected derivatives of primary amines. The method was also successful for the N-tert-butoxycarbonyl (N-BOC) protection of the amino acid, phenylalanine. The synthetic transformations are facilitated by the one-pot preparation of 1a-e followed by the direct reaction with the amines or amino acid. The present method thus offers an efficient and convenient protocol for the in situ preparation of triazolopyridine reagents to be used directly for the protection of amines and amino acids. N-Acyl- and N-alkoxycarbonyl triazolopyridines (1a-e) were readily prepared in 4 steps from 4-aminopyridine (4) by amine protection, pyridine nitration, nitro reduction and diazotizations/cyclizations. All reactions offer the advantages of rapid conversions in high yields under very mild conditions.