Debenzylation, catalytic

Addition of chiral lithium (5)-(a-methylbenzyl)benzylamide to tert-butyl 1-cyclopentenecarboxylate (77) at -95 °C, followed by quenching with 2,6-di-ter/-butylphenol, gave 78 in 98% diastereomeric excess. 78 was debenzylated catalytically and, after acidic hydrolysis and desalting on Dowex resin, afforded pure cispentacin 5 (Scheme 12) [94]. 

Debenzylation of the benzyloxy groups in 156 and 158 to 157 and 159 respectively was achieved, without affecting the aromaticity of the system, by catalytic hydrogenolysis in the presence of palladium-on-charcoal (86TL3127 89JHC991) (Scheme 61). 

Catalytic debenzylation of 10-(dibenzylamino)-6-(4-rerr-butylphenyl)-3,4-dihydro-2//-pyrimido[2,l-n]isoquinoline 421 (R = PhCH2) over a 5% Pd/C catalyst under hydrogen at atmospheric pressure in acidified EtOH at ambient temperature afforded the 10-amino derivative 421 (R = H) (98JMC1050). 

Aminonitrile formation on 125 with potassium cyanide and piperidine hydrochloride affords the derivative, 135. Hydrolysis as above gives the corresponding amide (136). Debenzylation is accomplished by catalytic reduction. Alkylation of the secondary amine with the side chain (96) used in the preparation of diphenoxylate affords pirintramide (138) This compound, interest-... 

Fluorodehydroxylation of 5-benzyl-5//-dibenz[f>,/]azepin-10(lli/)-one (47) with hydrogen fluoride and sulfur tetrafluoride followed by catalytic debenzylation of the product 48 provides access to 10-fluoro-5//-dibenz[ft,/]azepine (49).134... 

The synthesis is straightforward because for the preparation of the tetrapyrranc a bipyrrole can also be used as a central unit to which a benzyl 5-(acetoxymethyl)pyrrole-2-carboxylate can be attached as the terminal pyrrole rings. Debenzylation by catalytic hydrogenation then gives the desired tetrapyrrane building block 68. 

Table 1 Catalytic performance of the debenzylation reaction on different types of supported palladium catalyst. ...

In order to select a suitable catalyst, a variety of Pd/C catalysts were screened. Table 2 shows that the dechlorinated by-product was minimized to the level less than 1% as the catalyst metal loading increased from 3% to 10%. The catalytic activity for the debenzylation reaction was examined and compared based on the rate of hydrogen uptake (Figures 1 and 2). 

During the enantiospecihc total synthesis of ajmalin-related alkaloids, (-)-suaveoline and (-)-raumacline, N-debenzylation of the hydrochloride salt of the alkaloids was performed with 10% Pd/C (0.12 mol Pd/mol compound) in absolute EtOH at room temperature and 1 atm of hydrogen for 1 or 2 hours. When this catalytic debenzylation was performed, however, using 10% Pd/C (0.28 mol Pd/mol compound) in MeOH for 5 hours, N-methyl derivatives were produced in good yield (Scheme 4.91).339,340... 

A convenient procedure for the lactonization of alkenols has been recently revealed by Borhan and coworkers [19]. This methodology was successfully applied in the total synthesis of (+)-tanikolide (7-37), a natural product of marine origin which exhibits antifungal activities. Thus, when alkenol 7-36 is subjected to soluble oxone and a catalytic amount of 0s04, a smooth domino oxidative cleavage/lactonization process takes place which leads, after debenzylation, to the desired product in good overall yield (Scheme 7.12). 

Ethyl 6-amino-4,5-difluoro-l-methyl-7-oxo-li/,7//-pyrido[3,2,l-i/]cinno-line-8-carboxylate (84, R = H) was prepared from the 6-benzylamino derivative 84 (R = CH2Ph) by catalytic debenzylation over Pd/C in a mixture of ethanol and acetic acid (92EUP470578,92MIP1). 

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