Brønsted Acid-Catalyzed Addition Reaction of 5-Aminopyrazoles with 4-Aryl-1,2,4-triazole-3,5-diones

Abstract

An organocatalytic addition reaction of 5-aminopyrazole with 4-aryl-1,2,4-triazole-3,5-dione has been developed. Using 20 mol% of diphenyl phosphate as the catalyst, moderate to high yields are obtained for a variety of aminopyrazole-embedded 1,2,4-triazolidine-3,5-diones (urazoles) under mild reaction conditions.

Keywords

5-Aminopyrazole - Addition reaction - Urazoles - Organocatalysis - Aza-Heterocycle

Publication History

Received: 14 August 2025

Accepted after revision: 17 October 2025

Accepted Manuscript online:
17 October 2025

Article published online:
25 November 2025

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• 5 CCDC no 2476941 contains the crystallographic data of compound 3a.
• 6 General procedure for the synthesis of compound 3a: In an oven dried round bottom flask, 1a (0.1 mmol), 2a (0.1 mmol), 20 mol% of diphenyl phosphate were taken. 1 mL of toluene was added to the reaction mixture and stirred at rt for 1 day. Completion of the reaction was checked by TLC. After the completion of reaction, solvent was concentrated and the reaction mixture was directly purified by column chromatography on silica gel eluting with hexane/ethyl acetate (45/55) to afford desired product 3a.
• 7 Analytical data for the compound 3a: 3a was obtained as a pale yellowish solid in 65% yield (30.29 mg) after column chromatography. R _f = 0.40 in 3:2 ethyl acetate/hexane; ¹H NMR (500 MHz, CDCl₃) δ 7.59 (s, 2H), 7.41 (d, J = 15.8 Hz, 6H), 7.28 (s, 3H), 7.18 (s, 1H), 7.08 (s, 1H), 6.91 (s, 1H), 4.00 (s, 2H), 1.23 (s, 9H). ¹³C NMR (126 MHz, CDCl₃) δ 155.47, 154.48, 151.76, 149.22, 148.64, 144.20, 137.72, 131.59, 131.30, 130.26, 129.73, 128.82, 128.79, 128.20, 127.50, 127.43, 127.35, 124.12, 97.38, 35.70, 31.5.