Synthesis of 1,2,4-triazolo[1,5-a]pyridines
A copper-catalyzed reaction under an atmosphere of air provides 1,2,4-triazole derivatives by sequential N-C and N-N bond-forming oxidative coupling reactions. Starting materials and the copper catalyst are readily available and inexpensive. A wide range of functional groups are tolerated.
S. Ueda, H. Nagasawa, J. Am. Chem. Soc., 2009, 131, 15080-15081.
The biologically important 1,2,4-triazolo[1,5-a]pyridines were readily synthesized from N-(pyridin-2-yl)benzimidamides via PIFA-mediated intramolecular annulation via a direct metal-free oxidative N-N bond formation in short reaction times and high yields.
Zheng, S. Ma, L. Tang, D. Zhang-Negrerie, Y. Du, K. Zhao, J. Org. Chem., 2014, 79, 4687-4693.
An I2/KI-mediated oxidative N-N bond formation reaction enables an environmentally benign synthesis of various 1,2,4-triazolo[1,5-a]pyridines and other 1,5-fused 1,2,4-triazoles from readily available N-aryl amidines in an efficient and scalable fashion.
L. Song, X. Tian, Z. Lv, E. Li, J. Wu, Y. Liu, W. Yu, J. Chang, J. Org. Chem., 2015, 80, 7219-7225.
[1,2,4]Triazolo[1,5-a]pyridines have been prepared in good yields from 2-aminopyridines by cyclization of N-(pyrid-2-yl)formamidoximes under mild reaction conditions with trifluoroacetic anhydride.
E. Huntsman, J. Balsells, Eur. J. Org. Chem., 2005, 3761-3765.