Synthesis of Polyfunctional Pyridines via Copper-Catalyzed Oxidative Coupling Reactions

Abstract

An efficient and concise approach for the synthesis of polysubstituted pyridines has been achieved through copper-catalyzed oxidative sp C-H coupling of oxime acetates with toluene derivatives. Besides, benzylamine and p-toluenesulfonylhydrazone were also introduced to react with oxime acetates to enrich the diversity of this synthetic method. These transformations provide highly flexible and facile preparation of substituted pyridines and thus are useful in practical synthesis.

Synthesis of Pyridine Derivatives from Acetophenone and Ammonium Acetate by Releasing CH4

“…For examples, in 2016, our group developed copper-catalyzed synthesis of pyridines via oxidative sp 3 CÀ H coupling of oxime acetates with toluene derivatives (Scheme 1a). [11] The next year, we employed acetophenones, toluene, and NH 4 OAc as the starting materials, in combination with oxidizing terbutylhydroperoxide (TBHP), for synthesizing pyridines (Scheme 1b). [12] In 2018, our group achieved copper-catalyzed synthesis of pyridines by the cyclization of ketoxime carboxylates and N-aryl glycine esters (Scheme 1c).…”

Synthesis of triphenylpyridines via an oxidative cyclization reaction using Sr-doped LaCoO3 perovskite as a recyclable heterogeneous catalyst

“…The yield of 2,4,6-triphenylpyridine in the cyclization without the La 0.6 Sr 0.4 CoO 3 catalyst was similar to that of the cyclization using the La 0.6 Sr 0.4 CoO 3 catalyst (Scheme 2g). The reaction between (1), (7), and (7b) produced 3 products (16, 16b, and 16c) in similar yields under the standard conditions (Scheme 2h). These results suggest that (Z)-3-amino-1,3diphenylprop-2-en-1-one (12) may be the intermediate in this reaction, and that the transformation of (Z)-3-amino-1,3diphenylprop-2-en-1-one (12) to 2,4,6-triphenylpyridine (16) could proceed in the absence of the La 0.6 Sr 0.4 CoO 3 catalyst.…”

“…The cyclization of the ketoxime (7) and benzaldehyde (5) generated 2,4,6-triphenylpyridine (16) in high yield (92%), which demonstrates that benzaldehyde (5) may be the key intermediate in this reaction (Scheme 2e). The reaction between the ketoxime (7) and benzaldehyde (5) did not proceed in the presence of the antioxidant TEMPO, indicating that a radical process may be involved and that the interaction of TEMPO with the radical species generated in the catalytic cycle may have cease the transformation (Scheme 2f). (Z)-3-Amino-1,3diphenylprop-2-en-1-one (12) was synthesized and allowed to undergo the cyclization with the ketoxime 7under two different conditions.…”

A new route to triphenylpyridines utilizing ketoximes as building blocks via cascade reactions under iron‐organic framework catalysis

“…Following this, the benzoyl radical species ( D ) were produced from benzaldehyde ( 5 ) via a SET process with Fe (III) . Simultaneously, the reductive cleavage of N‐O bond of ketoxime acetate ( 1 ) by Fe (II) species offered the radical ( E ), which would be further reduced by a Fe (II) species to give the Fe (III) imine anion complex ( F ) . Tautomerism of ( F ) afforded ( G ), which reacted with the benzoyl radical ( D ) to give ( H ).…”