An Improved Synthesis of 3-Substituted 1,2,4-Triazolo[4,3-a]pyridines and 1,2,4-Triazolo[4,3-b]pyridazines

Palladium‐Catalyzed Coupling of Aldehyde‐Derived Hydrazones: Practical Synthesis of Triazolopyridines and Related Heterocycles

“…With suitable conditions for the palladium‐catalyzed coupling reaction in hand, our focus shifted to identifying mild conditions for the oxidative cyclization. Previously iodobenzene diacetate,9a copper(II) chloride,9b bromine,9c,d lead(IV) acetate,9d and chloramine‐T9e have been utilized for this transformation. Most of these reagents suffer from the formation of large amounts of toxic by‐products, which can impact product isolation and have a negative environmental impact.…”

Palladium‐Catalyzed Coupling of Aldehyde‐Derived Hydrazones: Practical Synthesis of Triazolopyridines and Related Heterocycles

“…[8] We recently reported the reactions of chloropyridines with benzoic hydrazide but, owing to competing side-reactions, only mediocre yields (30-50 %) of the desired coupling product were obtained with 2,4-dichloropyridine. [3] As oxidative approaches to triazoles are known, [1,9] the intermediate C seemed to be a suitable candidate to explore this synthetic approach (Scheme 1). Attempts to access this intermediate by introduction of the hydrazine through palladium-catalyzed coupling with benzophenone hydrazone, followed by benzophenone hydrolysis and condensation with benzaldehyde, failed at the benzophenonedeprotection step.…”

Synthesis of new derivatives of 3‐aryl‐1,5‐dimethyl‐1H‐[1,2,4]triazolo[4′,3′:1,2]pyrimido[4,5‐e][1,3,4]oxadiazines as potential antiproliferative agents

“…Numerous methods for the synthesis of 1,2,4-triazoles have been reported in the literature, which includes utilizing toxic reagents such as phosphorus oxychloride [12], lead tetraacetate [12,13], and bromine [13,14] as well as other oxidative reagents like chloramines T [15], iodobenzene diacetate [16,17], iron(III) chloride [18], and CuCl 2 [19]. The synthesis of 1,2,4-triazoles through electrochemical method [20] have also been reported.…”