No abstract

The hydrogenation of ethyl 4- R-2,4-dioxobutyrates (R = phenyl, 2-furyl) at 5% Pt/Al 2 O 3 catalyst, modified with cinchonidine, and at palladium black was investigated. The former had low activity under the conditions we tested. The main products during the hydrogenation of these compounds at palladium black are ethyl 4-R-2-hydroxy-4-oxobutyrates. The yield of the phenyl derivative amounts to 68.5%, while the yield of the corresponding 2-furyl derivative amounts to 97%. In the last case ethyl 2-hydroxy-4-oxo-4-(2-tetrahydrofuryl)butyrate was detected as impurity. The optimum conditions for the formation of ethyl 2-hydroxy-4-phenylbutyrate (yield 88.2%) were determined.Keywords: ethyl 4-substituted 2,4-dioxobutyrates, platinum and palladium catalysts, hydrogenation.The derivatives of 4-substituted 2-hydroxybutyric acids are valuable synthons for the production of antihypertensive substances, homoamino acids, hydroxamic acids, and other compounds [1,2].We studied the hydrogenation of sodium 2-oxo-4-phenyl-, 4-(2-furyl)-2-oxo-, 2-oxo-4-(2-thienyl)-, and 2-oxo-4-(3-pyridyl)butenoates at nickel and palladium catalysts.During the hydrogenation of sodium 2-oxo-4-phenylbutenoate at nickel catalysts the corresponding salt of 2-hydroxy-4-phenylbutyric acid is formed [3].The use of palladium black and 10% Pd/C catalyst leads to the formation of sodium 2-oxo-4phenylbutyrate. During the hydrogenation of sodium 4-(2-furyl)-2-oxobutenoate at Raney nickel catalyst the corresponding 4-(2-furyl)-2-oxobutyrates and 4-(2-furyl)-2-hydroxybutyrates and aliphatic compounds from hydrogenolysis of the molecule of the original compound are formed [4].During the hydrogenation of sodium and ethyl 2-oxo-4-(2-thienyl)butenoates at Raney nickel the corresponding derivatives of 2-oxo-4-(2-thienyl)butyric acid and 2-hydroxy-4-(2-thienyl)butyric acid are formed [5]. Palladium catalysts secure the more selective formation of the corresponding oxo compound than Raney nickel. The formation of ethyl 2-oxo-4-(2-tetrahydrothienyl)butyrate in addition to the above-mentioned compounds was also observed during the hydrogenation of ethyl 2-oxo-4-(2-thienyl)butenoate at palladium black.During the hydrogenation of sodium 2-oxo-4-(3-pyridyl)butenoate at palladium black the reaction products were sodium 2-oxo-4-(3-pyridyl)butyrate and 2-hydroxy-4-(3-pyridyl)butyrate and hydrogenolysis products. The reaction takes place by a parallel-consecutive mechanism [6].During the hydrogenation of derivatives of 4-substituted 2-oxobutenoic acids the double bond is saturated, and the carbonyl group is partly hydrogenated. The latter depends on the composition of the catalyst and on the structure of the initial compound. __________________________________________________________________________________________

Hydrogenation O 0220 Hydrogenation of Ethyl Esters of 4-Phenyl-and (2-Furyl)-Substituted 2,4-Dioxobutyric Acids at PalladiumBlack. -The optimization of the hydrogenation conditions is reported. -(SLAVINSKA, V.; SILE*, D.; ROZENTHAL, G.; MAUROPS, G.; POPELIS, J.; KATKEVICH, M.; STONKUS, V.; LUKEVICS, E.; Chem. Heterocycl.

Acids. -A new method for the synthesis of enalapril (III), a highly effective ACE inhibitor, by reductive alkylation of alanylproline (I) with 2-oxo-4-phenylbutenoate (II) is developed. Alkylation using the corresponding saturated α-oxo acid occurs with diminished diastereoselectivity. Reductive alkylation of alanylproline (I) with the 2-thienyl analogue of (II) also takes place asymmetrically, however, strong poisoning of the catalyst by the sulfur-containing compound is observed. -(SLAVINSKA, V.; SILE, D.; CHIPENS, G. I.; BALODIS, Y.; ROZENTHAL, G.; VENTERIS, K.; LUKEVICS, E.; Chem. Heterocycl.