From N-substituted thioamides to symmetrical and unsymmetrical 3,4,5-trisubstituted 4H-1,2,4-triazoles:: Synthesis and characterisation of new chelating ligands

An improved protocol for the synthesis of N-substituted pyridine-2-thiocarboxamides under the conditions of the Willgerodt-Kindler reaction, employing a catalytic amount of sodium sulfide nonahydrate, has been developed. Following this protocol, eight thioamides carrying aromatic or aliphatic N-substituents have been prepared in good to excellent yields. Condensation of these thioamides or their S-alkylated congeners with hydrazides in refluxing 1-butanol has afforded eight unfused 3,4,5-trisubstituted 4H-1,2,4-triazoles in good yields, including four examples of the otherwise not easily obtainable 4-alkyl-3,5-diaryl-4H-1,2,4-triazoles. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.