Hypervalent Iodine Oxidation of Hydrazones of Some Nitrogen Heterocyclic Ketones and Aldehydes: An Efficient Synthesis of Fused 1,2,3-Triazoloheterocycles

Synthesis, oxidation and dehydrogenation of cyclic N,O‐ and N,S‐acetals. Part III. Transformation of N,O‐acetals: 3‐acyl‐1,3,4‐oxadiazolines

“…Hypervalent iodine oxidation [32] has been reported to transform alkoxycarbonyl (ald)imines into oxazoles with C O bond formation [33], but to rearrange 2 -oxazolines with C O bond cleavage [34]. Transformation of arylhydrazines [35] and hydrazones [36] into ethers, as well as carboxylic acid hydrazides into N,N-diacylhydrazines [37], heterocyclization of hydrazones with C N [38] or N N [39] bond formation, degradation of carboxylic acid hydrazides [40] to parent acids, Hofmanntype rearrangement [41] or conversion of carboxamides to hydrazines with N N bond formation [42], regeneration of the carbonyl from (acyl)hydrazones [43], from oximes [44], and from dithianes [45] have also been described.…”

Electrochemical Synthesis of [1,2,3]Triazolo[1,5‐a]pyridines through Dehydrogenative Cyclization

“…[1,2,3]Triazolo[1,5‐ a ]pyridines, which exist in equilibrium with the ring‐opening diazo form in solution, have been employed as convenient precursors for carbene species in the synthesis of functionalized pyridine derivatives and several other N‐heterocycles (Scheme a) . Synthesis of [1,2,3]triazolo[1,5‐ a ]pyridines has been achieved through oxidative cyclization of hydrazones of 2‐acylpyridines employing stoichiometric chemical oxidants such as MnO 2 ,– Ag 2 O, NiO 2 , and PhI(OAc) 2 or more recently copper‐catalyzed aerobic oxidation …”

Oxidative cyclization in the synthesis of 5‐ and 6‐membered N,O‐heterocycles

“…1,2,3-Triazole fused heterocycles have been prepared by PIDA-mediated oxidation of N-heterocyclic hydrazones [56]. The reagent has also been used for the synthesis of 1,3,4-oxadiazole and 3 -1,3,4-oxadiazoline derivatives from N-acyl-hydrazones and N-phenylsemicarbazones [57].…”