Recyclable Heterogeneous Copper(II)-Catalyzed Oxidative Cyclization of 2-Pyridine Ketone Hydrazones Towards [1,2,3]Triazolo[1,5-a]pyridines

Abstract

The heterogeneous copper(II)-catalyzed oxidative cyclization of 2-pyridine ketone hydrazones was achieved in ethyl acetate at room temperature in the presence of an MCM-41-anchored bidentate 2-aminoethylamino copper(II) catalyst [MCM-41-2N-Cu(OAc)2], in the presence of air as the oxidant, yielding a wide variety of [1,2,3]triazolo[1,5-a]pyridines in mostly good to high yields. The present method was also applied to the direct one-pot synthesis of [1,2,3]triazolo[1,5-a]pyridines from 2-acylpyridine derivatives and hydrazine monohydrate. Importantly, this supported copper(II) catalyst could be conveniently obtained via a simple procedure from easily available and inexpensive reagents, recovered by filtration of the reaction mixture, and reused at least seven times without a significant loss of catalytic activity.

Access to Amides and Lactams via Pyridotriazole as a Transformable Directing Group

“…To a mixture of p -toluenesulfonyl hydrazide (931 mg, 5.0 mmol) and 3.0 mL of methanol was rapidly added 2-benzoylpyridine (916 mg, 5.0 mmol). , Within a few minutes, tosylhydrazone began to crystallize. The reaction was stirred for another 1 h and then cooled in an ice bath.…”

Supported Metal Catalysts for the Synthesis of N-Heterocycles

“…More recently, Cai et al moved their attention to copper species anchored onto MCM-41 mesoporous silica. In more detail, a MCM-41-anchored bidentate 2-aminoethylamino Cu(II) complex (named MCM-41-2N-Cu(OAc) 2 ) was synthesized and then tested in the oxidative cyclization of 2-pyridine ketone hydrazones 241 [176]. Reactions were carried out in ethyl acetate as the solvent, with 5 mol% of Cu loading, at room temperature for 30-180 min, affording a variety of 1,2,3-triazolopyridines 243 in good to excellent yields (Scheme 75a).…”

“…In both studies, the authors found high recyclability for the supported palladium catalyst, as it was used for eight consecutive cycles with no evident loss of its catalytic activity. cyclization of 2-pyridine ketone hydrazones 241 [176]. Reactions were carried out in ethyl acetate as the solvent, with 5 mol% of Cu loading, at room temperature for 30-180 min, affording a variety of 1,2,3-triazolopyridines 243 in good to excellent yields (Scheme 75a).…”

Sequential Organocatalytic Synthesis of [1,2,3]Triazolo[1,5‐a]quinolines

“…In this regard, there are several procedures in the literature for the preparation of these N ‐containing polycycles, mainly involving cyclization reactions [12] . Although most of these methods are very effective, and despite the significant recent advances, some limitations are still present, which includes the use of transition metals, such as Fe, [12c] Cu, [12d–f] or Pd, [12g–i] and require various reaction steps and complex starting materials, which are challenging to prepare and environmentally incompatible [12j–l] …”