Structural requirements in chiral diphosphine-rhodium complexes. X1 asymmetric homogeneous hydrogenation of z-N-acetyldehydroamino acids and esters with (1R,2R)-trans-1,2-bis(diphenylphosphinomethyl)cyclobutane/rhodium(I) complexes.

Robert Glaser, Jeanine Blumenfeld, Menachem Twaik

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Abstract

Z-α-acetamidocinnamate esters were hydrogenated with neutral rhodium(I) complexes containing (1R,2R)-trans-1,2-bis(diphenylphosphinomethyl)cyclobutane. Increasing the steric bulk of the alcohol moiety in the unsaturated esters had little influence upon the optical purity of the N-acetylphanylalanine ester products. In the series Me, Et, i-Pr, and t-Bu the optical purity decreased from 44 % ee-(R) [Me] to 40 % ee-(R) [t-Bu]. The chiral cyclobutane diphosphine appears to be only slightly more effective than the heterocyclic DIOP when ring-substituted Z-α-acetamidocinnamic acids are hydrogenated with neutral rhodium(I) complexes without the addition of triethylamine. Addition of triethylamine to the solvent blend seems to be more beneficial to the cyclobutane analogue than to DIOP.

Original languageEnglish
Pages (from-to)4639-4642
Number of pages4
JournalTetrahedron Letters
Volume18
Issue number52
DOIs
StatePublished - 1 Jan 1977

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