期刊
JOURNAL OF ORGANIC CHEMISTRY
卷 66, 期 11, 页码 3848-3853出版社
AMER CHEMICAL SOC
DOI: 10.1021/jo001770w
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Solvent effects on helicity induction in zinc bilinone (ZnBL) derivatives bearing chiral auxiliaries at their 19-positions were investigated by using circular dichroic spectroscopy and H-1 NMR experiments. In ZnBLs 1 and 2, which possess (R)-2-methyl-1-phenylpropyloxy and (R)-1-phenylethyloxy groups at their 19-positions, respectively, the efficiency of helicity induction was significantly affected by employed solvents (78-95% de in 1 and 33-89% de in 2). The free energy changes of the P-M interconversion of 1 and 2 were linearly in proportion to reduction in polarizability of solvents: lower polarizability of solvents led to better efficiency of helicity induction in 1 and 2. With the support of the H-1 NMR study in addition to the molecular modeling previously reported, it was indicated that the solvophobic van der Waals interaction between the alkyl group in the chiral auxiliary and the A-ring of the bilinone skeleton in the preferred conformer plays a crucial role in determining the efficiency of helicity induction in I and 2.
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