1 -Alkoxycarbonyl-1,2,4-triazole

The alkoxycarbonyl protecting groups can also be introduced into amines by, triazolides (Table 4—7). With A-tert-butoxycarbonyl-1,2,4-triazole the tert-butoxy-carbonyl protecting group (Boc) is transferred readily onto amino functions of primary amines, trimethylbenzyl ammonium salts of amino acids, or peptides.[ 1965 Alternatively, the Boc group can be transferred with terf-butylphenylcarbonate in the presence of 1,2,4-triazole. In this latter approach the triazolide is presumably formed as an intermediate. ... 

A different result was obtained in the cycloaddition to methylenecyclo-propanes 216-218 tearing alkoxycarbonyl substituents on the cyclopropyl ring. In this instance, 1,2,3-triazoles 220 isomeric with the triazolines 219 were formed in the reaction [57]. The formation of triazoles 220 is rationalised by the intermediate formation of triazolines 219, which are unstable under the reaction conditions and undergo a rearrangement to the aromatic triazoles via a hydrogen transfer that probably occurs with the assistance of the proximal ester carbonyl (Scheme 35). The formation of triazoles 220 also confirms the regio-chemistry of the cycloaddition for the methylene unsubstituted methylene-cyclopropanes, still leaving some doubt for the substituted ones 156 and 157. 

With acyl and alkoxycarbonyl azides, 2 -triazoles are isolated, although the l.ff-isomers are detected as intermediates. The reaction is not very general it fails with the corresponding sulfonium ylids, and fairly minor changes in substituents on the phosphorus ylid result in the formation of diazoketones rather than triazoles. ... 

Acyl- and 1-alkoxycarbonyl-l,2,3-triazoles are readily isomerized to the 2iEf-isomers in the presence of triethylamine or other bases. The... 

The parent 2(3/i/)-oxazolone moiety functions as a bifunctional leaving group when carboxyl groups are activated for acylations and condensations, similar to other five- and six-membered heterocycles such as imidazole, triazole, and 2-pyridinethiol. The excellent leaving ability of a 2(3//)-oxazolone moiety has led to the development of versatile reagents. Thus, 3-acyl- and 3-alkoxycarbonyl-2(3//)-oxazolones serve as ready-to-use -type agents for the regioselective and chemoselective N-protection of amino alcohols, amino phenols and polyamines. 

With acyl and alkoxycarbonyl azides, 2//-triazoles are formed by isomerization of the 1H compounds,410 and changes in R1 and R2 substitution lead to diazo compounds and iminophosphoranes rather than triazoles,408,411,412,415 owing to competitive addition to the C=P bond. Reaction of cyanogen azide with a-acylphosphorus ylides leads to 1-cyanotriazoles, which undergo in situ ring opening to give N-cyano-a-diazoimines.417... 

Copper(I) chloride can be an effective catalyst in multicomponent reactions, such as in the synthesis of 5-alkoxycarbonyl-4-aryl-3,4-dihydrop3nimidine-2-(l//)-ones, the synthesis of quinoline derivatives (eq 69), and the synthesis of fully substituted triazoles. The use of CuCl as an additive is also reported in cross-metathesis reactions leading to significant turnover enhancement. ... 

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