Selective debenzylations

Pd/CPS4 catalyst without using inhibitor (12). As shown in Figure 3, the reaction requires selective debenzylation versus dehalogenation of the... 

S. Y Wang, and J. P. Chen et al., Selective Debenzylation in the Presence of Aromatic Chlorine on Pd/C Catalysts Effects of Catalyst Types and Reaction Kinetics , paper presented at 20th Organic Reactions Catalysis Society Meeting, March 21-25, 2004, Hilton Head Island, SC, USA. 

Selective Debenzylation in the Presence of Aromatic Chlorine on Pd/C Catalysts Effects of Catalyst Types and Reaction Kinetics... 

BOCNH OBn multiphasic bOCNH Figure 6.28 Selective debenzylation of BOC-protected serine. 

Depending upon the reaction conditions, selective debenzylation or debenzylation and saturation of the pyridine moiety of benzyloxy derivatives of 4//-pyrido[l,2-a]pyrimidin-4-ones 333, 336 and 338 could be carried out by catalytic hydrogenation over palladium-on-charcoal. 

Oxidation of OH-2, 3, or 4 of sucrose has also been used as a first step towards many other derivatives. When 2-O-benzyl sucrose is transformed to its hepta-benzoate, selective debenzylation can provide the isolated 2-OH group. This... 

We took advantage of this observation in order to effect selective debenzylations, once an allylic appendage is attached to the sugar. For example, when the polybenzylated allyl-C-glucopyranoside 7 (10) is treated with iodine in THF at 0 °C, the bicyclic compound 8 is obtained (85 15 in favor to the 2 R isomer), which upon treatment with zinc and acetic acid undergoes a reductive elimination affording the C-glucoside 9 selectively deprotected at C-2. (11)... 

The corresponding acid 64 was prepared with anhydrous trifluoroacetic acid. This same acid was also obtained by selective debenzylation of the above mentioned dibenzylether 30, which links this synthesis with that of 7-oxa-PGFla. The keto acid 65 was prepared with Jones reagent and the ketogroup then protected as the ethylene ketal by converting the acid simultanously to the ester 66. 

Removing the BOC-group of 476 with HC1 in EtOH and selective benzylation at the less hindered /V-atom with 4-fluorobenzyl chloride in EtOH delivered the 1,5-oxazocine 477 in 74% yield. The regioisomer 478 was obtained by benzylation first, followed by removal of the BOC group (84%). Selective debenzylation of 479 with H2 and Pd/C yielded 1,5-oxazocine 478 (82%) (Scheme 95) <2005TL5577>. 

Ten years later, a Japanese group led by Oikawa developed a mechanistically related method for the selective debenzylation of substituted benzyl ethers based on the reagent 2,3-dichloro-S,6-dicyanobenzo-quinone (DDQ). In contrast to the trityl tetrafluoroborate reaction, the oxidation proceeds at room temperature in the presence of water. Furthermore, under these convenient and essentially neutral conditions, many functional groups, including other common protecting groups, such as isopropylidine, methoxy-methyl, benzyloxymethyl, tetrahydropyranyl, acetyl, r-butyldimethylsilyl, benzyl, benzoyl and tosyl, are unaffected. As a result of the hig levels of selectivity which can be achieved, this method for the depro-... 

The hydrogenolysis of benzyl esters provides a means for the selective eonversion of the ester to the acid under mild conditions. Substituted dibenzyl malonates are easily converted to the substituted malonic acids by hydrogenolysis in neutral medium thus avoiding the acyl cleavage or decarboxylation which can result from base or acid catalyzed ester hydrolysis (Eqns. 20.26-27).5 . 58 Monobenzylmalonates are selectively debenzylated and decarboxylated to give the substituted acetic esters. 

The —C = C— functionality remains intact In 1986, results from a systematic study revealed that successful, selective debenzylation of substrates containing a variety of functional groups could be achieved with 2.2 equiv. calcium (Tab. 4.1) [12]. These groups include benzene, furan, and cyclopropyl rings allyhc, furfuryl, cyclo-propyalkoxyl, and tert-butyldimethlysilyl ethers and the C = C triple bond. 

Debenzylation of quaternary ammonium salts. The selective demethylation of quaternary ammonium salts noted by Shamma (1, 1107, ref. 3) has been found by Japanese chemists1 to be applicable to selective debenzylation of such salts. Thus N,N-dibenzyl-N,N-dimethylammonium chloride is converted in 85% yield into N,N-dimethylbenzylamine. The reagent also effects deallylation of quaternary ammonium salts. 

The Tafel colour reaction has been re-examined ° and a method, of potential value in synthesis, has been developed for the selective debenzylation of N-benzyl quaternary salts this involves the treatment of the salt at 0—5 C with lithium n-propylmercaptide (PrSLi) in HMPA. 

Selective debenzylation of 4-methoxyphenyl benzyl ether in hexamethyl phosphorictriamide has been affected by addition of sodium metal and stirring of the mixture at 100°C under nitrogen during 3 hours to furnish a 93% yield of... 

Selective debenzylation. Benzyl groups of quaternary ammonium salts can be removed selectively by treatment with n-propylthiolithium in HMPT at... 

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