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]. 

Diazonium ions react with all known nucleophiles. The addition of hydroxide, alkoxide, cyanide and sulfite ions does not belong to the subject of this review, but the formation of diazoamino compounds (1,3-triazenes) formed with ammonia, primary and secondary amines does. In analogy with the other reactions discussed in this paper, where carbon atoms are the site of attack by diazonium ions (C-coupling), these reactions are called N-coupling reactions. 

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... 

Zollinger and coworkers" " have also studied the diazo coupling reactions of diazo-nium salts extensively. The proposed mechanism for the N-coupling reaction between a diazonium ion and an aromatic amine involves formation of an amine-diazonium ion complex, 9, which is converted into a cr-complex, 10, which subsequently loses a proton to base forming the product (equation 43), where B is any base, i.e. the amine, the solvent or... 

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