Hydrogenolysis of C—N bond

Hydrogenolytic cleavage of the C-N bond takes place more easily than that of the C-C bond but with more difficulty than that of the C-O bond. Activation 

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]. 

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Formation of hydroxyl quinoline must have been initiated by ionic reactions that involved and OH ions. Hydrogenation by Ha enables the heterocyclic ring to be saturated, and this can be followed by hydrogenolysis of C-N bonds that first open the hetero-ring and then convert the resultant aliphatic and aromatic amine intermediates to hydrocarbons and ammonia (24). Also direct attack of OH on quinoline may have led to formation of hydroxyl quinoline. It has been suggested that both ionic reaction and free radical capping are possible under supercritical conditions (25). 

Hydrogenolysis of C-N and C-0 Bonds Hydrodenitrogenation and Hydrodeoxygenation. - The mechanisms of these reactions (abbreviated hdn and... 

Hydrogenation of N-heterocycles -Hydrogenation of arene rings -Hydrogenolysis and cleavage of C-N bonds... 

From the examples described in the preceding Sections and in Chapter 3, Section 3.3.2 (p. 84), it can be concluded that the hydrogenation of N-heterocyles is much more facile than C-N bond breaking reactions when soluble transition metal complexes are employed as models for HDN catalysis this is in parallel to what has been observed on metal sulfide surfaces. Indeed, while several examples of efficacious homogeneous catalysts for the hydrogenation of N-heterocycles to the corresponding cyclic amines (partially or fully saturated) are available (see Chapter 3), only one case of C-N bond hydrogenolysis promoted by a metal-complex in solution has been described so far. Moreover, the real nature of this process is not clearly defined. 

It is widely accepted that a benzyl-nitrogen bond is not as readily cleaved as a benzyl-oxygen bond. The presence of nitrogen can, however, influence the hydrogenolysis of C-O bonds. It has been reported that butylamine completely prevented the hydrogenolysis of the benzylic C-O bond [62]. The same effect was observed for molecules containing both benzylic C-O and C-N bonds [62,63]. In a mixture of A-benzylcyclohexylamine and benzyl cyclohexyl ether only the C-N bond was hydrogenolyzed on Pd/C, whereas in the presence of HCl the... 

Catalytic Hydrogenolysis of Carbon-Huonne Bonds it-Bond Participation Mechamsm Hudlicky, M J Fluorine Chem 44, 345-359 58 n o C) S ... 

The dissolving metal reduction is not suitable, because it effects a cleavage ol the benzylic C-N bond. b The cleavage of the N-N bond by hydrogenolysis is affected by some racemization. 

Treatment of the 0,0-dibenzyl derivative of norneoenactin with 10% Pd/C in MeOH under hydrogen atmosphere resulted in the rapid deprotection (within 1 h) of the starting material. However, reduction of the benzyl ether functionality, without the concomitant hydrogenolysis of the N-O bond, required fine tuning of the conditions. When the hydrogenolysis was carried out using 20-25 mol % of 10% Pd/C at 20 or 30 mM concentrations for 22-31 hours, a... 

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

It was also reported that the other compound in the reaction mixture was hydrogenated on 10% Pd/C (0.2 mol Pd/mol) in AcOH for 5 hours with 80% yield without hydrogenolysis of the C-N bond (Scheme 4.73).316... 

During the asymmetric synthesis of a-aminophosphonates (14 in Fig. 4.4), numerous attempts to cleave the benzylic C—N bond, involving catalytic or transfer hydrogenolysis, resulted in epimerization at the a-carbon.319... 

Hydrogenolysis of the N-O bond was also observed on Pd/C catalyst in MeOH (Scheme 4.99).344... 

Both the benzylic C-O and the C-N bonds were cleaved during the synthesis of (4)-lactacystin. The hydrogenolysis of the oxazoline moiety on Pd/C, Pd(OH2)/C, or Pd black in MeOH proved unsuccessful, but catalytic transfer... 

Microwave-induced organic reaction enhancement chemistry was used for the hydrogenolysis of the C-N bond in lactams. To a solution of a-vinyl (3-lactams in ethylene glycol were added HC02NH4 and 10% Pd/C catalyst then this mixture was irradiated in a microwave oven (Scheme 4.108).357... 

Hydrogenolysis of one C-N bond in diazaspiroalkanes (31) can occur on platinum or nickel catalysts (Scheme 4.109).358... 

Hydrogenolysis of hydroxybenzamidines to benzamidines has always been of interest to the hydrogenation chemists. The hydrogenolysis of the N—O bond in these compounds was performed on 4% Pd/C in AcOH at 60°C and 60 psi hydrogen pressure (Scheme 4.138).531,532... 

Nitroso Acetals Hydrogenation of a nitroso acetal on Ra-Ni at 1 atm H2 for 1 hour afforded a ketone via the hydrogenolysis of the N-O bonds and the cyclohexyl C—O bond (Scheme 4.147).546... 

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