Carbon-nitrogen bonds oxidation additions

Transition metal complex-catalyzed carbon-nitrogen bond formations have been developed as fundamentally important reactions. This chapter highlights the allylic amination and its asymmetric version as well as all other possible aminations such as crosscoupling reactions, oxidative addition-/3-elimination, and hydroamination, except for nitrene reactions. This chapter has been organized according to the different types of reactions and references to literature from 1993 to 2004 have been used. 

Replacement of the boron atom for a nitrogen atom is possible with a suitable aminating agent. Treatment of a trialkylborane with a chloramine, prepared in situ by oxidation of ammonia or an amine with sodium hypochlorite, provides a method to form a carbon-nitrogen bond (5.26). The transformation of an alkene to an amine by overall addition of ammonia is much less straightforward than hydration and this methodology, although used less frequently than oxidation with peroxide, provides a solution to this problem. 

Carbon-Nitrogen Bond Formation. Apart from the CAN-mediated reactions in which solvent (e.g., acetonitrile) incorporation results in carbon-heteroatom bond formation, the oxidative generation and subsequent addition of heteroatom-centered radicals to alkenes or alkynes provide means of direct construction of carbon-hetereoatom bonds. ... 

Reductive eliminations from nickel(ll) complexes to form carbon-heteroatom bonds in amines and ethers have also been reported. Like the mechanisms for oxidative additions to Ni(0) and Pd(0) that cleave carbon-heteroatom bonds, the mechanisms for reductive elimination from nickel(II) and palladium(II) complexes to form caibon-heteroatom bonds are different from each other. Most reductive eliminations from Ni(II) to form carbon-nitrogen bonds occur after oxidation of the Ni(II) to Ni(III) with ferro-ceruum, oxygen, or iodine (Equations 8.53 and 8.54). Reductive eliminations from Ni(II) to form carbon-oxygen bonds in ethers also requires oxidation of ttie Ni(II) to Ni(III) (Equation 8.55). In contrast, reductive eliminations from Ni(II) to form the ester group of a lactone occurred after a proposed insertion of CO into the nickel-carbon bond of an oxametallacycle without oxidation. Reductive eliminations from isolated arylnickd complexes to form amines and ethers have not been reported. 

The oxidative addition of allyl bromide to Os3(GO)io(NCMe)2 has also been studied. No carbon-nitrogen bonds are formed cluster opening to linear trinuclear clusters is of some interest.The reaction of lightly ligated triosmium clusters with fullerene G6o has been successfully attempted in this case also, no G-N bonds are formed. 

N-AryInitrones (XIII) formed by oxidation of N-hydroxy-N-methyl arylamines, show high reactivity toward carbon-carbon and carbon-nitrogen double bonds in non-aqueous media (21,203) (Figure 10). Under physiological conditions, however, it appears that N-arylnitrones exist as protonated salts that readily hydrolyze to formaldehyde and a primary N-hydroxy arylamine and efforts to detect N-arylnitrone addition products in cellular lipid, protein or nucleic acids have not been successful (204). Nitroxide radicals derived from N-hydroxy-MAB have also been suggested as reactive intermediates (150), but their direct covalent reaction with nucleic acids has been excluded (21). 

A less common reactive species is the Fe peroxo anion expected from two-electron reduction of O2 at a hemoprotein iron atom (Fig. 14, structure A). Protonation of this intermediate would yield the Fe —OOH precursor (Fig. 14, structure B) of the ferryl species. However, it is now clear that the Fe peroxo anion can directly react as a nucleophile with highly electrophilic substrates such as aldehydes. Addition of the peroxo anion to the aldehyde, followed by homolytic scission of the dioxygen bond, is now accepted as the mechanism for the carbon-carbon bond cleavage reactions catalyzed by several cytochrome P450 enzymes, including aromatase, lanosterol 14-demethylase, and sterol 17-lyase (133). A similar nucleophilic addition of the Fe peroxo anion to a carbon-nitrogen double bond has been invoked in the mechanism of the nitric oxide synthases (133). 

Reduction of a mixture of two aryl halides is not generally a good route to the mixed biaryl. Either a statistical mixture of the three possible biaryls is formed or, if one aryl halide is more reactive, this forms a single biaryl after which, the second aryl halide reacts with itself. The principal exception to this generalisation involves the reduction of a 1 1 mixture of an aryl bromide and 1-chloropyridine. Oxidative-addition to Ni(o) is faster for the carbon-bromine bond. The second oxidative-addition to ArNi(i) is faster for the 2-chloropyridinc, possibly due to complexation from the pyridine nitrogen. Overall, the 1-aryipyridine is formed in 55-80 % yields [200]. 

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