Protecting groups benzyl

Section 27 16 Carboxyl groups are normally protected as benzyl methyl or ethyl esters Hydrolysis m dilute base is normally used to deprotect methyl and ethyl esters Benzyl protecting groups are removed by hydrogenolysis... 

Catalytic hydrogenolysis of an O-benzyl protective group is a mild, selective method introduced by Bergmann and Zervas to cleave a benzyl carbamate (> NCO—OCH2C6H5 > NH) prepared to protect an amino group during pep-... 

Na, ammonia. These conditions also remove cyanoethyl- and benzyl-protective groups. Phosphorothioates are similarly deprotected. 

Hydrogenation of the product 147 removes the benzyl protecting groups and at the same time reduces the triazine to its dihydro derivative 148. A roundabout scheme is required for dehydrogenation due to the sensitivity of the intermediates. The product is thus converted to its silyl ether 149 exposure to air results in oxidation and desilylation. There is thus obtained the antineoplastic agent fazarabine (150), also known as ara-A C. 

Ni prior to use by refluxing it for 3 h with acetone, in order to suppress hydrogenolysis of the benzylic protecting groups (51). 

As seen in the retro-synthetic Scheme 5.3, intermediate 15 is useful for both routes. The choice of benzyl protection group was made based on the robust stability of benzyl phenol ethers toward most reactions and several possible avenues to remove it, although it was reported from Medicinal Chemistry that benzyl group removal via hydrogenolysis posed challenges in this compound. The choice of iodide substitution was born out of the known high reactivity of iodides in the Ullmann-type coupling reaction with alcohols and the robust stability of aryl iodides in many other common reactions. 

For removing both the O-benzyl and N-benzyl protecting groups, 10% Pd/C and 1.8 ml HCl was added to a solution of the starting compound in 2 ml EtOH and the mixture was stirred under hydrogen for 14 hours (Scheme 4.38).174... 

Benzyl esters of phosphoric acid have been employed also with success in organic synthesis. Usually palladium catalysts are used to remove the benzyl protecting group (Scheme 4.50). 

The benzyl—nitrogen bond is not so easily cleaved as the benzyl—oxygen bond, unless the O-benzyl group is sterically hindered. This difference in activity allows the selective removal of the O-benzyl function in a molecule containing both N-benzyl and O-benzyl protecting groups. The selectivity can be reversed if the amine is protected by the Cbz group. If a small amount of amine (e g., butylamine) is added, then the selective removal of N-benzyl amines can be achieved.292... 

D. P. Curran, R. Ferritto, Y. Hua, Preparation of a Eluor-ous Benzyl Protecting Group and its Use in a Fluorous Synthesis Approach to a Disaccharide , Tetmzhedron Lett. 1998, 39, 4937. 

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