Stereoselective Michael Addition of Glycine Anions to Chiral Fischer Alkenylcarbene Complexes. Asymmetric Synthesis of β-Substituted Glutamic Acids
作者:Jesús Ezquerra、Concepción Pedregal、Isabel Merino、Josefa Flórez、José Barluenga、Santiago García-Granda、María-Amparo Llorca
DOI:10.1021/jo9819739
日期:1999.9.1
The reaction of lithium enolates of achiral N-protected glycine esters with chiral alkoxyalkenylcarbene complexes of chromium provided the corresponding Michael adducts with either high anti or syn selectivity depending on the nature of the nitrogen protecting group, and high diastereofacial selectivity when carbene complexes containing the (-)-8-phenylmenthyloxy group were employed. Subsequent oxidation
非手性N-保护的甘氨酸酯的烯醇锂与铬的手性烷氧基链烯基碳烯配合物的反应提供了相应的迈克尔加成物,根据氮保护基团的性质而具有高的反选择性或顺式选择性,而当含()的卡宾配合物具有高的非对映选择性使用-)-8-苯基薄荷基氧基。金属卡宾部分的随后氧化,接着是胺基的脱保护和两种羧酸酯的水解,提供了对映体富集的天然和非天然立体化学的3-取代的谷氨酸。备选地,当在氧化之前进行脱保护步骤时,形成环状氨基碳烯络合物,其最终导致光学活性的3-取代的焦谷氨酸。