A well‐defined N‐heterocyclic carbene‐palladacycles (NHC‐Pdcycle) by introducing alkoxy group was synthesized, and its structure was confirmed using single‐crystal X‐ray diffraction. The complex as catalyst exhibited high catalytic activity in Buchwald‐Hartwig and Suzuki‐Miyaura coupling reactions involving (hetero)aryl chlorides. Remarkably, the protocol with a wide range of substrate compatibility is suitable for the gram‐scale synthesis of Piribedil, a clinical drug for the treatment of Parkinson's disease, highlighting its potential applications in pharmaceutical synthesis.
The core-shell magnetic mesoporous microspheres immobilized NHC-palladacycles (NHC = N-heterocyclic carbene) catalyst with constrained aliphatic linker group (Fe 3 O 4 @mSiO 2 @NHCÀ Pd) were readily prepared by the welldesigned method, which showed higher palladium loading (0.20 mmol g À 1 ) and higher catalytic activity than the nonmesoporous catalysts (Fe 3 O 4 @SiO 2 @NHCÀ Pd) prepared by the same process in the Suzuki-Miyaura cross-coupling reactions of aryl chlorides and aryl boronic acids. Herein, Fe 3 O 4 @mSiO 2 @NHCÀ Pd could be used 12 times without significant activity loss, and no palladium leakage was detected in both the product and catalytic residue, highlighting the efficiency of our strategy for immobilizing the catalyst. Remarkably, this approach allows the synthesis of important drug intermediates 2-aryl-4-aminoquinazolines and o-tolylbenzonitrile (OTBN).
Palladium‐catalyzed C−N bond activation of amide is a important but very challenging research area in organic chemistry. This reaction represents a powerful and straightforward method for the preparation of various carbonyl compounds under mild reaction conditions. One notable advancement in this area is related to the design and development of multifunctional NHC ligands and other throw‐away ligands. The reasonable design of ligands could not only improve the activity of catalyst, but also help to adjust the reaction selectivity. In this review, we summarized the structure‐activity relationship of those catalysts with different ligand skeletons and their applications in cross‐coupling reactions including Suzuki‐Miyaura coupling, Buchwald‐Hartwig amination and direct C−H acylation, via amide C−N bond activation. On this basis, we analyze the current bottlenecks encountered in Pd‐NHC‐catalyzed amide C−N activation reactions, and envisage the future development of this field.
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