1.2.3- Triazoles, synthesis from oximes

By Dehydration of a-Diketone Hydrazone Oximes Another general method of synthesis of 2i/-triazoles involves intramolecular elimination of water from adjacent hydrazone and oxime functions (Scheme 32). The usual reagent is acetic anhydride, but others, including phosphorus pentachloride and urea, have been used. 

Examples include the synthesis of 3-amino-l,2,4-oxadiazoles starting from 3-acylamino-5-methyl-l,2,4-oxadiazole <2002H811> and 2-aryl-l,2,3-triazoles from l,2,4-oxadiazole-3-ketone arylhydrazones <1999T12885, 2006JOC5616>. Oximes, hydrazones, formamidines, and thioureas of the furazan series also undergo base-catalyzed mononuclear rearrangements <2004RCB1121>. Nucleophilic attack at N(3) takes place in the benzofuroxan series. For example, reaction with secondary amines leads to o-nitroarylhydrazines (Scheme 55). 

The cyanides 1408-1412 have all been synthesized by dehydrating their carbox-aldoximes with acetic anhydride [1070-1074]. A pteridine synthesis yielded 75% of 6-cyano-l,3-dimethyUumazine 1408 [1070]. N-Acetyl (3-phenyl-l,2,4-triazolo-5-yl)-thiolacetonitrile 1409 was obtained as the condensation product from a triazole derivative and chloro acetaldehyde, followed by oximation and dehydration, in 79% yield [1071]. endo-l-Cyano-3-acetoxy-8-oxabicyclo[3.2.1]oct-6-ene 1410 (89%) is an intermediate in the synthesis of ll-oxatricyclo[5.3.1.0 Jundecane [1072]. A synthesis of loi,25-dihydroxY-18-norvitamin Dj and la,25-dihydroxy-18,19-dinorvitamin Dj requires the 8j8-acetoxy-des-A,B-cholestane-18-nitrile 1411 (86%) [1073]. A new route to spirooxindoles, a tricyclic system found in a number of interesting natural products, requires the cyanide 1412 (72%) as a key intermediate [1074]. 

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