C-N coupling reaction

The presence of two types of catalytic centers (e.g., oxidative and reductive) in the same material can give rise to the possibility of multi-step photocatalysis in a one-pot procedure. C-C coupling, for example, is a field of great interest and a recent very good review was published [221]. C-N coupling reactions are also of interest. 

Blaser, H.-U., Indolese, A.,Naud, F. etal. (2004) Industrial R D on catalytic C—C and C—N coupling reactions apersonal account on goals, approaches and results. Advanced Synthesis and Catalysis, 346 (13-15), 1583-1598. 

Equation 11.44 Solid support aryl/heteroaryl C-N coupling reactions. 

Scheme 5.12 Iron-catalyzed C-N coupling reaction developed by Taillefer et al.

Scheme 8.4 Stepwise synthesis of the tetrapeptide 18, containing the sequence 14-17 of the human proinsulin C-peptide, from the methoxy(phenyl)carbene complex 16 via the carbene chromium derivative 17 as the intermediate (Gly-OMe and Pro-OMe were the methyl esters of glycine and proline). The C—N coupling reactions in steps (1)—(4) were carried out using the DCCD/HOSU method, explained in [35]...

Hartwig has reported a DPPF/Pd-catalyzed C-N coupling reaction between a diarylamine and an aryl nonaflate, Eq. (63) [64bj. The coupling below proceeded in 95 -100% yield (NMR) and was used in a strategy to prepare oligo(m-aniline) compounds. 

Benzophenone imine may be used as an ammonia equivalent with halopyridines as well. The coupHng of the bromopyridine below, followed by deprotection via transamination with hydroxylamine, proceeded in 81% yield over the two steps, Eq. (158) [ 128]. Analogously, Puttman found that allylamine could also be used as an ammonia equivalent in the C-N coupling reactions of halopyridines [114]. 

The Grubbs catalyst requires a vacant coordination site to become active. In the active species, the NHC ligand is superior to the phosphane, simply because of the greater net electron donicity. In many other C-C and C-N coupling reactions, the picture is different. 

A similar situation prevails in other C-C and C-N coupling reactions since they also contain a PdL key intermediate. It is therefore no surprise that mixed NHC/phosphane ligand systems have been employed for the Mizoroki-Heck, Suzuki-Miyaura and StiUe reactions [238,255-258]. In all these cases, the incorporation of a phosphane ligand instead of the second NHC ligand improves the activity of the catalytic reaction. Similar results are reported for the allylic alkylation of dimethylmalonate using mixed NHC/phosphane palladium catalysts [252]. 

Lin and Tao used P(Z-Bu)3 for the synthesis of benzo[a]aceanthranylene core compounds (acen) 98. Pure red-emitting devices were fabricated using acen as both holetransporting and emitting materials [157]. Palladium-catalyzed aromatic C—N coupling reactions and cyclization were carried out in one pot in the presence of Pd(OAc)2 and r-Bu3P [157]. 

Clearly, the use of stoichiometric amounts of organo tin compounds is the main disadvantage of this type of C-N coupling reaction both for ecological reasons and with regard to practicability. Thus, from an industrial point of view the aim was to replace the tin amides by simpler amino sources, ideally the amines themselves. Again independently, Buchwald et al. [8] and Hartwig et al. [9] reported... 

Loiseleur and co-workers developed a process for the preparation of imatinib base, in which the final step involved a Pd2(dba)3CHCl3-catalyzed C-N coupling reaction with the of use of rac-BINAP as ligand. Others provided an improved process based on Loiseleur s method. However, the concerns of these approaches are the use of a toxic, hazardous reagent cyanamide and using relatively high-cost palladium as the catalyst for C-N coupling reaction. 

Synthesis of faceted Cu nanoparticles and their use as catalysts in C-N coupling reactions (including the three-component, one-pot Mannich reaction) with high selectivity for the desired products was recently reported by Wang et al. [263]. 

The application of inexpensive photoactive copper complexes has given great impulse to visible light-mediated photoredox catalysis, e.g. for C-C and C-N coupling reactions. Irradiation of Cu-complexes both triggers metal centred single electron transfer processes and assists the Cu-catalysed elemental steps, in which the substrate is covalently bonded. Successful extension of cooperative copper photocatalysis to other reactions is expected for the near future. " ... 

Chouhan et al. (2007) found that Cu(I)-catalyzed C-N coupling reactions between aryl/heteroaryl bromides and azoles could be efficiently facilitated by the proline-functionalized magnetic nanoparticles (MNPs). Generally, the desired A-aryl/A-heteroaryl azoles (including pyrazoles, indoles, and benzimidazoles) were synthesized in good to excellent yields (Scheme 4.27). 

Li et al. developed the solvent-free C-N coupling between A-heterocycles and aryl/ heteroaryl halides promoted by the nano-Cu2O/l,10-phen/tetra-n-butylammonium fluoride (TBAF) catalytic system. Different types of CU2O were evaluated, and the studies showed that CU2O nanoparticles (especially the cubic form) were the most efficient for the C-N coupling reactions (Scheme 4.28) (Tang et al., 2008). 

The formation of C—N bonds is an important transformation in organic synthesis, as the amine functionality is found in numerous natural products and plays a key role in many biologically active compounds [1]. Standard catalytic methods to produce C—N bonds involve functional group manipulations, such as reductive amination of carbonyl compounds [2], addition of nucleophiles to imines [3], hydrogenation of enamides [4—8], hydroamination of olefins [9] or a C—N coupling reaction [10, 11]. Recently, the direct and selective introduction of a nitrogen atom into a C—H bond via a metal nitrene intermediate has appeared as an attractive alternative approach for the formation of C—N bonds [12-24]. 

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