Dibenzyl esters, hydrogenolysis

High-molecular-weight aliphatic ketones of the type RCOCH,R are made by acylation of substituted dibenzyl esters of malonic acid followed by hydrogenolysis and decarboxylation/ ... 

The dicarboxyic acid 66 (alkylidenesuccinic acid), obtained by hydrolysis and decarboxylation of the triester 65, resembles the product (half-ester) 73 of the Stobbe condensation (Scheme 11-21) [21]. In order to prepare the half-ester, carbonylation in benzyl alcohol to prepare the monomethyl ester and dibenzyl ester 75, followed by hydrogenolysis of the dibenzyl ester, was attempted, expecting the formation of the halfester. However, /S-keto ester 76 was obtained, an entirely different product (Scheme 11-22) [22]. The mechanism of this unexpected reaction is unknown. 

The first, and still widely used, polymer-supported ester is formed from an amino acid and a chloromethylated copolymer of styrene-divinylbenzene. Originally it was cleaved by basic hydrolysis (2 N NaOH, FtOH, 25°, 1 h). Subsequently, it has been cleaved by hydrogenolysis (H2/Pd-C, DMF, 40°, 60 psi, 24 h, 71% yield), and by HF, which concurrently removes many amine protective groups. Monoesterification of a symmetrical dicarboxylic acid chloride can be effected by reaction with a hydroxymethyl copolymer of styrene-divinylbenzene to give an ester a mono salt of a diacid was converted into a dibenzyl polymer. ... 

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. 

Dibenzyl phosphite was treated with sulphuryl chloride in toluene followed by cyanamide in aqueous alkali to give the salt (114). This was condensed with sarcosine methyl ester to give the imidazolinone (115) which after hydrogenolysis gave phosphocreatinine (116) Scheme 5.27.) [122],... 

Derivative 57a was synthesized by reacting the phosphate directly with p-hydroxyacetophenone bromide. Derivative 57b was synthesized from hydrogenolysis of the pHP dibenzyl phosphate ester. For 35 and 57c, the pHP monophosphate (57b) was first protected as the corresponding ketal that was then coupled with ADP or GDP, respectively. The caged ATP and GTP analogs were then obtained by hydrolysis of the ketal. Yields and quantum efficiencies for the disappearance of the pHP phosphate esters are given in Table 69.16. 

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