Acid hydrogenolysis

The blocking and deblocking of carboxyl groups occurs by reactions similar to those described for hydroxyl and amino groups. The most important protected derivatives are /-butyl, benzyl, and methyl esters. These may be cleaved in this order by trifluoroacetic acid, hydrogenolysis, and strong acid or base (J.F.W. McOmie, 1973). 2,2,2-Trihaloethyl esters are cleaved electro-lytically (M.F. Semmelhack, 1972) or by zinc in acetic acid like the Tbeoc- and Tceoc-protected hydroxyl and amino groups. 

During the synthesis of siderophores, the simultaneous removal of the benzyl, p-nitrobenzyl, and -butoxicarbonyl protecting groups was accomplished under acidic hydrogenolysis conditions (H2, 10% Pd/C in DMF-HC1-H20). 

Other methods of minor importance include the displacement of a thio or alkylthio group with ammonia giving aminopyridazines in poor yield, cleavage of a thiourethane with acid, hydrogenolysis of isoxazolo[3,4-d]pyridazin-7-ones or 4,7-diones, - or ring opening with acid of an imidazolo[4,5-d]pyridazine to yield 4,5-diamino - 3,6-dimethoxypy ridazine. ... 

The degradation of the Senecio alkaloids continues to be effected by saponification or hydrogenolysis. The use of alkali in the hydrolysis does not alter the necine moiety but it may cause a change in the geometrical configuration about an a,j8-oarbon-carbon double bond in the necic acid. Hydrogenolysis provides important information as to the location of the esterified hydroxyl on the necine, and subsequent conversions permit a decision as to which end of a dicarboxylic necic acid (in the cyclic diesters) is attached to the allylic or primary hydroxyl of the necine. 

Phenylsulfonyl)ethyl phosphites and phosphates are stable in the presence of acids, towards acid, hydrogenolysis, and tertiary amines in aprotic solvents, enabling the orthogonal removal of numerous other protecting groups. 

Platinum oxide/acetic acid Hydrogenolysis of benzyl ethers... 

Cyclopropane and Cyclopropene Adds.— The undesirable physiological properties of cyclopropene acids such as malvalic acid (20 R = H) and sterculic acid (21 R = H) and their presence, albeit in small amount, in cottonseed oil has aroused interest in these compounds. The content of cyclopropene acids is reduced by heating with palladium catalysts, though not with nickel or platinum catalysts. Palladium treatment cleaves the cyclopropene ring and produces methyl- and methylene-substituted acids. Hydrogenolysis of cyclopropane acids is reported to give methyl-substituted fatty acids which can be identified by their g.l.c. behaviour on capillary columns. The chemical reactions of cyclopropene acids (malvalic and sterculic) shown in Scheme 5 have been reported. ... 

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