Conjugate addition of lithium N-tert-butyldimethylsilyloxy-N-(α-methylbenzyl)amide: asymmetric synthesis of β2,2,3-trisubstituted amino acids
作者:Scott A. Bentley、Stephen G. Davies、James A. Lee、Paul M. Roberts、Angela J. Russell、James E. Thomson、Steven M. Toms
DOI:10.1016/j.tet.2010.04.027
日期:2010.6
Conjugate addition of the homochiral ammonia equivalent lithium N-tert-butyldimethylsilyloxy-N-(α-methylbenzyl)amide to a range of α,β-unsaturated esters gives the corresponding β-amino esters in moderate to good levels of diastereoselectivity. O-Desilylation and cyclisation furnishes homochiral isoxazolidin-5-ones in >99:1 dr after purification. Sequential alkylation of these templates proceeds to
的纯手性氨锂当量的共轭加成ñ -叔-butyldimethylsilyloxy- ñ - (α -甲基苄基)酰胺的范围内的α,β不饱和酯,得到相应的β氨基酯在中度至非对映选择性的良好水平。纯化后,O-去甲硅烷基化和环化可在> 99:1 dr下提供纯手性异恶唑烷-5-酮。这些模板的顺序烷基化进行后,纯化后得到相应的3,4-抗-二取代和3,4,4-三取代的衍生物作为单一非对映异构体。第一烷基化水平高非对映选择性的在烯醇化物的面发生反向Ç(3)-取代基,而第二烷基化的面部选择性则由手性中继效应决定,该效应取决于C(3)-和C(4)-取代基的相对空间体积。随后的氢解促进二者的切割位Ñ -α甲基苄基和在一个罐中的异恶唑烷-5-酮环内的N-O键,得到相应的β 2,2,3-三取代氨基酸直接。