Selective Homogeneous Hydrogenation of 3-Oxo-1,4-diene Steroids. II. Effects of Basic Additives and of para Substituents on the Hydrogenation with Dichlorotris(triphenylphosphine)ruthenium

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Abstract
The catalytic homogeneous hydrogenation of 1,4-androstadiene-3,17-dione (I) with dichlorotris(triphenylphosphine) ruthenium has been investigated in the presence of basic additives. The rate of hydrogenation increased with respect to added amines in the order pyridine<none<butylamine<aniline<diethylamine≅triethylamine. The hydrogenation was also promoted by the addition of calcium carbonate, but slightly retarded by that of sodium carbonate. The amount of triethylamine required for obtaining the maximum rate of hydrogenation has been determined. Addition of triethylamine also reduced the formation of 5α-androstane-3,17-dione produced by a different pathway from that for the formation of 4-androstene-3,17-dione (II), resulting in an increased selectivity for the formation of II. I was also hydrogenated with the ruthenium complexes having p-methoxy-, p-methyl-, and p-fluoro-substituted triphenylphosphines as ligands. The catalytic activity of the ruthenium complex was greatly enhanced by p-methoxyl and p-methyl groups and reduced by p-fluoro group when the catalyst was used in the presence of triethylamine.