On Ni catalysts for catalytic, asymmetric Ni/Cr-mediated coupling reactions |
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Authors: | Liu Xiang Li Xiaoyong Chen Yu Hu Yimin Kishi Yoshito |
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Affiliation: | Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA. |
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Abstract: | The importance of the Ni catalyst in achieving catalytic asymmetric Ni/Cr-mediated coupling reactions effectively is demonstrated. Six phenanthroline-NiCl(2) complexes 1a-c and 2a-c and five types of alkenyl iodides A-E were chosen for the study, thereby demonstrating that these Ni catalysts display a wide range of overall reactivity profiles in terms of the degree of asymmetric induction, geometrical isomerization, and coupling rate. For three types of alkenyl iodides A-C, a satisfactory Ni catalyst(s) was found within 1a-c and 2a-c. For disubstituted (Z)-alkenyl iodide D, 2c was identified as an acceptable Ni catalyst in terms of the absence of Z → E isomerization and the degree of asymmetric induction but not in terms of the coupling rate. Two phosphine-based Ni catalysts, [(Me)(3)P](2)·NiCl(2) and [(cy)(3)P](2)·NiCl(2), were found to meet all three criteria for D. The bond-forming reaction at the C16-C17 position of palytoxin was used to demonstrate the usefulness of the Ni catalysts thus identified. |
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