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Hydrogenolysis of Benzyl-Oxygen Bonds

The structure of the substrate influences the rates of hydrogenolyses. Over Pd, the rates of hydrogenolysis of benzyl derivatives increase in the order OH OR OAr OCOR, according to their leaving group ability. Therefore, ben- [Pg.130]


Pd/CaC03 is also used for the hydrogenolysis of benzyl-oxygen bonds.152 Hydrogenation and hydrogenolysis of an unsaturated benzyl ether over 5% Pt/ C and Pd(OH)2 gave the saturated and deprotected product.153 In contrast, transfer hydrogenolysis with 1,4-cylohexadiene or ammonium formate failed to provide the product cleanly, rapidly, or dependably. [Pg.137]

A more expected difference between platinum oxide and palladium-on-carbon was found in the hydrogenolysis of 5-phenyI-2-(3,4-dimethoxybenzyI)-2-oxazoline. Cleavage occurred at the benzyl-oxygen bond over both catalysts, but over platinum, the less substituted phenyl group was saturated as well (78). [Pg.144]

Benzyl-oxygen bonds may be cleaved under conditions mild enough to leave an allylic hydroxy group (759) or an easily reduced N—OH bond intact (65,80). N-Hydroxyamino acids can be prepared in good yield by hydrogenolysis of benzyl hydroxamates as shown in the synthesis of N -hydroxylysine (6) from 5 (777). [Pg.158]

The removal of a carbobenzyloxy group can be separated into two steps (Figure 1). The first step comprises the hydrogenolysis of the benzyl oxygen bond of the Cbz-protected amino acid 1 to form a carbamic acid intermediate 2 and toluene 3. The carbamic acid intermediate decaiboxylates to give the deprotected amino acid 4 and one equivalent of carbon dioxide 5. [Pg.494]

Both benzyl-oxygen and nitrogen-oxygen bonds undergo hydrogenolysis readily in the presence of a benzyloxy-nitrogen bond but it appears that the benzyl-oxygen bond can be made to cleave selec-... [Pg.142]

Allyl alcohols are deoxygenated under the same conditions used to break a benzyl oxygen bond. Over a palladium catalyst, loss of oxygen occurs along with double bond saturation. The presence of acids promotes hydrogenolysis. With platinum, nickel, or rhodium catalysts in neutral medium, progressively less oxygen... [Pg.525]

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... [Pg.420]


See other pages where Hydrogenolysis of Benzyl-Oxygen Bonds is mentioned: [Pg.157]    [Pg.130]    [Pg.130]    [Pg.584]    [Pg.233]    [Pg.417]    [Pg.157]    [Pg.130]    [Pg.130]    [Pg.584]    [Pg.233]    [Pg.417]    [Pg.525]    [Pg.401]    [Pg.638]    [Pg.163]    [Pg.164]    [Pg.396]    [Pg.132]    [Pg.143]    [Pg.173]    [Pg.151]    [Pg.260]    [Pg.277]    [Pg.132]    [Pg.143]    [Pg.173]    [Pg.450]    [Pg.322]    [Pg.528]    [Pg.141]    [Pg.904]    [Pg.765]    [Pg.1082]    [Pg.260]    [Pg.773]    [Pg.1106]    [Pg.198]    [Pg.230]    [Pg.139]    [Pg.99]    [Pg.139]    [Pg.155]    [Pg.573]    [Pg.58]   


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Benzylic bonds

Bonds hydrogenolysis

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