Hydrogenolysis carbon-nitrogen bonds

Hydrogenolysis is analogous to hydrolysis and ammonolysis, which involve the cleavage of a bond induced by the action of water and ammonia, respectively. Chemical bonds that are broken by hydrogenolysis reactions include carbon—carbon, carbon—oxygen, carbon—sulfur, and carbon—nitrogen bonds. An example of hydrogenolysis is the hydrodealkylation of toluene to form benzene and methane ... 

Cleavage of the carbon-nitrogen bond occurs in benzyloxycarbon amino compounds as a result of decarboxylation of the corresponding free carbamic acids resulting from hydrogenolysis of benzyl residues [725, 729, 7S0] (p. 151). 

Reductive Coupling. Formation of dicyclohexylamine (25) in hydrogenation of aniline probably involves addition of cyclohexylamine to an imine and subsequent hydrogenolysis of a carbon—nitrogen bond (11). 

Scheme 10.9 The hydrogenation pathway of amides to amines involving hydrogenolysis of the carbonyl carbon-nitrogen bond.

The stereochemistry of hydrogenolysis of carbon-nitrogen bonds has been studied with optically active 2-amino-2-phenylpropionic acid and its derivatives.85,121,122 Ethyl 2-amino-2-phenylpropionate (56, X = NH2, Y = OEt) was not hydrogenolyzed... 

Homolytic cleavage of simple aziridines with alkyl substituents or one aryl substituent takes the reaction path dictated by rupture of the less polar carbon-nitrogen bond, e.g. hydrogenolysis of 2,2-dimethylaziridine takes place as fol-lows - ... 

Hydrogenation of diarylamines yields dialicyclic amines, but hydrogenolysis of the carbon-nitrogen bond also occurs. Dehydrogenation of DPA yields catbazole and alkyl derivatives of DPA give acridines. Dehydrogenation with sulfur gives phenothiazines (12). 

Ester enolates which contain the chiral information in the acid moiety have been widely used in alkylations (see Section D.1.1.1,3.) as well as in additions to carbon-nitrogen double bonds (sec Section D.1.4.2.). Below are examples of the reaction of this type of enolate with aldehydes720. The (Z)-enolate generated from benzyl cinnamate (benzyl 3-phenylpropcnoate) and lithium (dimethylphenylsilyl)cuprate affords the /h/-carboxylic acid on addition to acetaldehyde and subsequent hydrogenolysis, The diastereoselectivity is 90 10. 

The most important C-N bond breaking reaction is the hydrogenolysis of the carbon-nitrogen O-bond. 

Palladium catalysts, mostly palladium on carbon and Pearlman s catalyst, are used for the hydrogenolysis of the benzyl—nitrogen bond. However, in some cases, platinum, nickel, and copper chromite catalysts have also been used. 

Phthalazinones are, so far, the only hydrazones in which, in acid solution, the carbon-nitrogen double bond has been shown to be saturated before the hydrogenolysis of the nitrogen-nitrogen bond.40 4-Methylphthalazinone (89) is thus reduced in the following steps to 1-methylphthalimidine (90). 

Palladium catalysts, usually Pearlman s catalyst [42] and Pd/C are used for the hydrogenolysis of benzyl-nitrogen bonds. Acetic acid, ethyl acetate, ethanol, or methanol are frequently used as solvents. Sometimes a small amount of a strong acid is added to the reaction mixture [54-56]. The bond rupture needs the adsorption of carbon [57]. The hydrogenolysis of C-N bonds occurs with inversion on both Pd and Ni [2,58]. 

The same was found for nitrogen-containing compounds protected by benzyl-oxymethyl groups. These compounds have two reactive bonds. The regioselectivity of the hydrogenolysis depends on the catalyst used. The carbon-oxygen bond was ruptured by use of Pd/C as catalyst whereas the rupture of the C-N bond occurred when hydrogenolysis was performed with Pd(OH)2 in MeOH (Scheme 8) [65]. 

Unexpectedly, hydrogenolysis of aziridines does not consistently result in cleavage of the bond betweon the nitrogen atom and the ksw-substituted carbon atom of the ring. Examples of hydrogenous. collected in Table 15, do not permit any further generalization about the aoope of the reaction. 

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