Structural requirements in chiral diphosphine-rhodium complexes. VI. Inhibition of the asymmetric hydrogenation of Z-methyl-α-acetamidocinnamate catalyed by diop-rhodium catalyst in the presence of Z-adamantyl or bornyl-α-acetamidocinnamate. |
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Authors: | Robert Glaser Jeanine Blumenfeld |
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Institution: | Chemistry Department, Ben Gurion University of the Negev, Beersheva, ISRAEL |
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Abstract: | The half-life period (6.6 mm.) for the hydrogenation of Z-methyl-a-acetamidocinnamate (catalyzed by a neutral DIOPRh complex) was found to be the same when the Me ester reduction was performed in the presence of equimolar quantities of the corresponding i-Pr or t-Bu ester unsaturated stbstrates. Neither the Me nor the i-Pr or t-Bu esters underwent appreciable Z,E-isomerization. The formation of N-acetylphenylalanine methyl ester product suffered inhibition when the hydrogenation reaction was performed in the presence of the corresponding bornyl or 1-adamantyl unsaturated esters (half-life period of the Me ester: 27 ~ 40 mm., respectively. The greater the inhibition of the Me ester unsaturated substrate, the more the bulky inhibitor itself underwent Z,E-isomerization. In the presence of inhibitors, the Me unsaturated substrate did not undergo appreciable Z,E-isomerization. |
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