No abstract

A series of novel 2‐(4‐(4‐chlorophenyl)‐1H‐pyrazol‐3‐yl)‐5‐(Aryl)‐1,3,4‐oxadiazoles were synthesized by unexpected aromatization during oxidative cyclization of 4‐(4‐chlorophenyl)‐4,5‐dihydro‐1H‐pyrazole‐3‐carbohydrazones using chloramine‐T as an oxidant. The hydrazones were derived from 4‐(4‐chlorophenyl)‐4,5‐dihydro‐1H‐pyrazole‐3‐carbohydrazide and various substituted aldehydes. The structure of the synthesized compounds was confirmed by FTIR, 1H NMR, 13C NMR, and mass spectral data. The synthesized compounds were evaluated for their antitubercular and antioxidant activities. All the compounds 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h and 5a, 5b, 5c, 5d, 5e, 5f, 5g, 5h showed good antitubercular activity against Mycobacterium tuberculosis (minimum inhibitory concentration = 25 µg/mL for 4f and 4g, 50–100 µg/mL for the rest). However, all the compounds exhibited poor antioxidant activity against 1,1‐diphenyl‐2‐picryl‐hydrazil free radical.

Fused 3,6‐disubstituted triazolothiadiazoles were synthesized in good yield from a rapid and convenient oxidative cyclization of N‐heteroaryl‐substituted hydrazones promoted by chloramine‐T trihydrate at ambient temperature. The structure of the synthesized compounds was confirmed by FTIR, 1H NMR, 13C NMR, and mass spectral data. The synthesized compounds were evaluated for their antioxidant and antitubercular activities. All the compounds 5a‐i and 6a‐i showed good antitubercular activity. However, only compounds 5a‐i showed good antioxidant activity.

Facile One Pot Synthesis of 8-Chloro-[1,2,4]triazolo[4,3-a]pyrazines via Oxidative Cyclization Using Chloramine T. -The reaction of 3-hydrazinylpyrazines with aldehydes and subsequent chloramine T promoted cyclization of the resulting hydrazone intermediates provides the title compounds. Further conversions via Suzuki-Miyaura and Sonogashira cross coupling reactions are also presented. -(MAL, S.; PRATHAP, K. J.; SMITH, S. C.; UMARYE*, J. D.; Tetrahedron Lett. 56 (2015) 22, 2896-2901, http://dx.

Facile Synthesis of 3,6-Disubstituted-1,2,4-triazolo-[3,4-b]-1,3,4-thiadiazoles via Oxidative Cyclization of n-Heteroaryl-Substituted Hydrazones and Their Biological Activity. -All the title triazolothiadiazoles (IV) (9 examples) and their hydrazone precursors (III) show good antitubercular activity. Moreover, compounds (III) exhibit good antioxidant activity. -(HIMAJA*, M.; PRATHAP, K. J.; MALI, S. V.; J. Heterocycl. Chem. 49 (2012) 4, 823-828, http://dx.