Lithiated 4-Isopropyl-3-(methylthiomethyl)-5,5-diphenyloxazolidin-2-one: A Chiral Formyl Anion Equivalent for Enantioselective Preparations of 1,2-Diols, 2-Amino Alcohols, 2-Hydroxy Esters, and 4-Hydroxy-2-alkenoates
作者:Christoph Gaul、Kaspar Schärer、Dieter Seebach
DOI:10.1021/jo0155254
日期:2001.5.1
provide 4-hydroxy-2-alkenoates (Scheme 5). The scope and limitations of the new, overall enantioselective transformation are determined, and the readily recovered chiral auxiliary used is compared with oxazolidinones of other substitution patterns (Scheme 7). The configuration of a number of products has been assigned by single-crystal X-ray diffraction (cf. Figure 5). These structures and similarities
标题中指定的杂环化合物(很容易从商业前体制备)具有一个空间受保护的C == O基团,因此BuLi在环外CH(2)基团上的直接锂化成为可能(3-> Li-3) 。锂化的N,S-乙缩醛衍生物(Li-3)非对映选择性地添加到醛(表2),不对称酮(表3),查尔酮(1,4-加成,方案2)以及N-膦酰基和N-磺酰亚胺类化合物中(表4)。Hg(O(2)CCF(3))(2)在THF /乙腈水溶液中对新形成的OH基的保护(方案3)和/或MeS / OH取代将N,S-乙缩醛转化为半缩醛(- > 20),其又容易裂解成醛,并回收手性助剂(方案1,方案4)。可以分离出这些醛(尤其是那些缺少α-羰基氢的醛),或者通过还原成(选择性保护的)二醇或氨基醇,添加格氏试剂或Li试剂(将二醇提供两个立体异构中心),氧化生成2-羟基酯或烯化生成4-羟基-2-链烯酸酯(方案5)。确定了新的整体对映选择性转化的范围和局限性,并将易