Ahern Theresa, Müller-Bunz Helge, Guiry Patrick J
Centre for Synthesis and Chemical Biology, Conway Institute of Biomolecular and Biomedical Research, University College Dublin, Belfield, Dublin 4, Ireland.
J Org Chem. 2006 Sep 29;71(20):7596-602. doi: 10.1021/jo060894r.
A facile route to a series of planar chiral N,O-ferrocenyl pyrrolidine-containing ligands with varying substituents at the nitrogen and oxygen donor atoms is described. The oxygen donor atom was introduced via a diastereoselective ortho-metalation of N-methylpyrrolidinyl and N-allylpyrrolidinyl ferrocene intermediates and was quenched with various ketones. The nitrogen substituent was varied through deallylation and subsequent derivatization of a secondary pyrrolidine. The efficacy of these novel ligands was investigated in the enantioselective addition of diethylzinc and diphenylzinc to aromatic aldehydes. The ligands proved highly effective in the diethylzinc addition to benzaldehyde that resulted in high yields of up to 99% and enantioselectivities (ee's) of up to 95%. The role of planar chirality was explored and the results indicated that the planar chirality, and not the central chirality, of the ferrocenyl ligands was the dominant stereo-controlling element. Employment of a mixed ethyl-phenylzinc reagent in the phenylation of aromatic aldehydes led to a mixture of the two additional products, and the phenylated product was obtained in up to 37% ee.
描述了一种简便的方法来合成一系列平面手性含氮、氧二茂铁基吡咯烷配体，这些配体在氮和氧供体原子上具有不同的取代基。通过N-甲基吡咯烷基和N-烯丙基吡咯烷基二茂铁中间体的非对映选择性邻位金属化引入氧供体原子，并用各种酮淬灭。通过脱烯丙基化和仲吡咯烷的后续衍生化来改变氮取代基。研究了这些新型配体在二乙基锌和二苯基锌对芳香醛的对映选择性加成反应中的效果。这些配体在二乙基锌加成到苯甲醛的反应中被证明非常有效，产率高达99%，对映选择性（ee值）高达95%。探索了平面手性的作用，结果表明二茂铁基配体的平面手性而非中心手性是主要的立体控制因素。在芳香醛的苯基化反应中使用混合的乙基-苯基锌试剂导致两种额外产物的混合物，苯基化产物的对映体过量值高达37%。
