Catalysts with carbon—nitrogen bond

Shaw concluded that hydrogenation of 3-alkyl-4-aminomethylene isoxazol-5-ones (184) in the presence of palladium catalyst resulted in the saturation of either the endocyclic double carbon-nitrogen bond or the exocyclic double C—C bond with the retention of the heterocyclic nitrogen-oxygen bond. Recent data reported by Kochetkov et al. on the properties, and in particular on hydrogenation, of isoxazolid-5-ones - indicate, however, that Shaw had probably ob-... 

The palladium based catalyst systems were also effective in the construction of carbon-nitrogen bonds on benzannulated five membered heterocycles. The 4-chloroindole derivative shown in 6.78. was coupled with piperazine in excellent yield, using a ferrocene based ligand.109 The analogous 5-bromo-benzimidazole derivative gave similar results (6.79.),110... 

Benzimidazoles bearing a halogen in the activated 2-position show a remarkable reactivity in palladium catalyzed carbon-nitrogen bond forming reactions. TV-protected 2-chlorobenzimidazoles reacted smoothly with a series of amines (6.81.). The activity of the aryl halide, besides the ready coupling of the chloro derivative, is also emphasized by the low catalyst loading used.112... 

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... 

At high temperatures with low catalyst concentration the formation of acetanilides is favored. Maleic anhydride and acetanilides may be formed directly from the mixed anhydride by an initial attack of the nitrogen on the acetate carbonyl, but this process would involve a seven membered ring transition state. Another possible route to the formation of maleic anhydride and the acetanilides is participation by neighboring carbonyl in loosening the amide carbon-nitrogen bond to the extent that the amine can be captured by acetic anhydride as shown in path D. 

EMDE DEGRADATION. Modification of the Hofmann degradation method for reductive cleavage of the carbon-nitrogen bond by treatment of an alcoholic or aqueous solution of a quaternary ammonium halide with sodium amalgam. Also used as a catalytic method with palladium and platinum catalysts. The method succeeds with ring compounds not degraded by the Hofmann procedure. 

Carbon-Nitrogen Bonds. Several groups have studied the synthesis of optically active a-amino acids from inexpensive and readily available a-haloesters by displacement with phthalimide in the presence of chiral cinchona catalysts [1 le,24h,24i,47e,60d,77]. Early studies, with chiral, non-racemic starting material, showed that this reaction occurs with partial... 

The available evidence indicates a nonconcerted mechanism which is depicted in Scheme 14. Oxidation of a Pd(0) species by the carbon-nitrogen bond of the allyle-nammonium ion gives cleavage to the 7r-allylpalladium complex and an enamine. Nucleophilic reaction by the enamine on the Pd salt then forms resultant imines after a loss of a proton. The role of co-catalyst CF3C02H is to form the N-allylenammonium ion, which reacts readily with the Pd(0) species. 

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. 

Tandem catalysis [1-10], which involves several catalytic cycles within the same medium to produce a desired product, is becoming increasingly important for the economic and environmental acceptability of the process. Copper salts are efficient catalysts in various transformations, including formation of carbon-carbon and carbon-nitrogen bonds [11-14], The author postulated they could play key parts in construction of complex nitrogen heterocycles with important biological activities through formation of multiple bonds [15-23]. 

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