Electrochemical Cyclization of Hydrazones and Amidines To Access Trisubstituted 1,2,4-Triazoles

Abstract

A KI-mediated electrochemical method has been developed for the synthesis of trisubstituted 1,2,4-triazoles from easily accessible hydrazones and amidines derivatives. The protocol provides various aryl and alkyl 1,2,4-triazoles in moderate to good yields with good functional-group tolerance and without the need for any chemical oxidants in an undivided cell.

Key words

electrosynthesis - hydrazones - amidines - triazoles

• References and Notes

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• 11 1,2,4-Triazoles 3ab–3oa; General Procedure Hydrazone 1 (0.6 mmol), amidine 2 (0.3 mmol), KI (1.0 equiv), K₃PO₄ (20 mol%), LiClO₄ (0.1 M), and MeCN–H₂O (6 + 1 mL) were added to an undivided cell (10 mL) equipped with a graphite-rod anode (diameter: 6 mm) and a Pt plate cathode (1 × 1 cm), and the mixture was stirred and electrolyzed under constant-current conditions (10 mA) at r.t. for 5 h. When the reaction was complete, the solvent was removed under reduced pressure and the residue was extracted with EtOAc (3 × 10 mL) and H₂O. The organic layers were combined and dried (MgSO₄), and the residue was purified by column chromatography [silica gel PE–EtOAc (5:1)]. 5-Methyl-1,3-diphenyl-1H-1,2,4-triazole (3aa)^3a Yellow solid; yield: 61%; mp 89–92 °C. ¹H NMR (400 MHz, CDCl₃): δ = 8.20–8.09 (m, 2 H), 7.50 (dd, J = 4.3, 1.7 Hz, 4 H), 7.47–7.39 (m, 4 H), 2.56 (s, 3 H). ¹³C NMR (101 MHz, CDCl₃): δ = 161.20, 152.83, 137.43, 130.67, 129.34, 129.17, 128.63, 128.47, 126.28, 124.57, 13.11.