Palladium carbon-nitrogen bond formation

Jiang L, Buchwald SL (2004) Palladium-catalyzed aromatic carbon-nitrogen bond formation. In de Meijere A, Diedeiich F (eds) Metal-catalyzed cross-coupling reactions, 2nd edn. Wiley-VCH, Weinheim... 

Not only acetylene derivatives do undergo palladium catalysed intarmolecular carbon-nitrogen bond formation with amines. The similar reaction of olefins in a Wacker-type process also leads to ring closure. (0-Aminopentenes bearing a suitable leaving group in the 4-position were converted to pyrroles in a cyclization-isomerisation-elimination sequence (3.65.),82... 

In certain cases, when the palladium or nickel catalyzed coupling is not efficient or fails completely, an alternate solution is provided by the use of copper based catalyst systems. The 5-iodouracil derivative shown in 7.77. was unreactive towards imidazole using either the Buchwald-Hartwig conditions or the copper(I) triflate promoted the carbon-nitrogen bond formation reported by Buchwald98 These latter conditions, however, were effective in coupling the iodouracil with a series of other amines (7.77.), The optimal catalyst system consisted of copper(I) triflate, phenantroline and dibenzylideneacetone (dba).99... 

Palladium-catalyzed carbon-nitrogen bond formation (for reviews see [86— 91]) has been considerably developed in the past decade and, due to the omnipresence of nitrogen-containing compounds in natural products such as alkaloids or non-natural functional targets such as electron-rich zr-systems,... 

Wolfe, J. P., Wagaw, S., Buchwald, S. L. An Improved Catalyst System for Aromatic Carbon-Nitrogen Bond Formation The Possible Involvement of Bis(Phosphine) Palladium Complexes as Key Intermediates. J. Arrr. Chem. Soc. 1996,118,7215-7216. 

Simple synthetic protocols for carbon-carbon and carbon-nitrogen bond formation using an air-stable palladium catalyst bearing an NHC ligand have been presented. The (IPr)Pd(allyl)Cl catalyst can be prepared on a large scale in high yield, better yet it is commercially available. Initial catalyst testing was performed on a small scale but the ease with which the described chemistry can be scaled up has now been shown. 

Palladium-Catalyzed Carbon-Nitrogen Bond Formation... 

In addition to simply mediating the formation of carbon-nitrogen bonds, palladium catalysis can be used to construct these precursors in concert with cyclization. One example of this was demonstrated by Barluenga, where palladium catalysis is employed to form two separate bonds first the carbon-carbon bond via the arylation of the azaallylic anion of imine 19, followed by catalytic carbon-nitrogen bond formation (Scheme 6.38) [50]. 

As an alternative to primary amines in these double carbon-nitrogen bond forming reactions, Maes has demonstrated that 22 can undergo consecutive palladium-catalyzed carbon-nitrogen bond formation with orfho-dihalopyridine derivatives (Scheme 6.42). This reaction proceeds in good yield with a number of amidine variants, and provides a route to the construction of polycyclic imidazoles [54]. 

I 13 Palladium-Catalyzed Aromatic Carbon-Nitrogen Bond Formation 13.3.3... 

---