Acylhydrazines 1.2.4- triazoles

PELLIZZARI REACTION. Formation of substituted 1,2,4-triazoles by die condensation of amides and acylhydrazines. When the acyl groups of the amide and acylhydrazine are different, interchange of acyl groups may occur, widi formation of a mixture of triazoles. 

The ease of forming C—N and C= N bonds as compared with the difficulty of N—N formation practically prescribes the use of hydrazines in the synthesis of 1,2,4-triazoles. Scheme 59 illustrates synthetic schemes that use one of the following (a) hydrazine, (b) an acylhydrazine, (c) amidrazone or (d) acylamidrazone. The dotted lines leave the presence or absence of a bond open. Thus in (a) possible reactants are (R COX, R COX and NH3) or (R CONHz and R COX) or (R COX and HjNCOR ) or (R CONHCOR ) X stands for a suitable leaving group, usually OH, H2O. 

Mostly, these compounds were synthesized by cyclocondensation of aldonic acid derivatives, such as lactones, imidate esters, or thioimidate esters, with acylhydrazines. Thus, reaction of the 2,5-anhydro-D-allono-l,6-lactone derivative 682 with aminoguanidine gave the 3-amino-5-(j8-D-ribofuranosyl)- ,2,4-triazole 684 (75TL985) (Scheme 182). 

Annelations with acylhydrazines or their equivalent derivatives are the cornerstone for many 1,2,4-triazoles syntheses. For example, thiosemicarbazides react with aroyl... 

Acylhydrazines, carboxamide acetals, and primary amines are cyclocondensed in an eflBcient one-pot three-component process to afford 3,4,5-trisubstituted 1,2,4-triazoles 17 [516] ... 

Bakulev et al. reported that 38 exclusively gives triazoles 40 after formation of transient diazo compounds 39 with tosyl azide [46]. As the authors did not obtain isomeric triazoles 41, resulting from cyclocondensation with the amide, these results clearly show that reaction of the acylhydrazine with the diazo moiety is highly favored (Scheme 13). Following the same strategy, l-arylsulfonyl-5-hydroxy-triazoles 42 were obtained in good yields (62-68%). 

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