ABSTRACT
Abstract The removal of carbobenzyloxy (Cbz or Z) groups from amines or alcohols is of high interest in the fine chemicals, agricultural and pharmaceutical industry. Palladium on activated carbon is the catalyst of choice for these deprotection reactions. Nitrogen containing modifiers are known to influence the selectivity for certain deprotection reactions. In this paper we show the rate accelerating effect of certain N-containing modifiers on the deprotection of carbobenzyloxy protected amino acids in the presence of palladium on activated carbon catalysts. The experiments show that certain modifiers like pyridine and ethylenediamine increase the reaction rate and therefore shorten the reaction times compared to non-modified palladium catalysts. Triethylamine does not have an influence on the rate of deprotection. Introduction Carbobenzyloxy groups are widely used as protective groups in organic synthesis (1). The removal of carbobenzyloxy groups is easily achieved via hydrogenolysis in the presence of heterogeneous catalysts at low hydrogen pressure and ambient temperature (2-4). Other examples for hydrogenolysis reactions where a σ bond is directly cleaved are debenzylation and hydrodehalogenation reactions. The effect of N-containing modifiers on the selectivity of debenzylation reactions has been previously reported. It was shown that the presence of a wide variety of mono and bifunctional aliphatic amines and pyridines selectively inhibit the cleavage of aliphatic benzyl ethers, whereas the reactivity of other functional groups was not effected. (5-6). In another work, the addition of triethylamine to the reaction mixture containing the palladium on carbon catalyst leads to the complete hydrogenolysis of an intermediate for the production of ABT-866, which otherwise would have stalled out (7).
