2,2-Disubstituted Oxazolidines, New Chiral Auxiliaeies Based on the Conformational Control at the Amide Linkage.

2,2-二取代的恶唑烷在4位上有一个手性中心，在以下方面起着有效的手性助剂作用：1)它们很容易从天然存在的α -氨基酸中以光学纯净的形式获得，2)它们的α、β不饱和酰胺衍生物稳定在Z-/s-顺式构象中，因此不饱和反应的引物位于4-屏蔽取代基附近，3)这种构象的稳定性被动态^1H NMR谱证实，4)一个氧化腈环加成到α，2,2-二取代恶唑烷的-不饱和酰胺衍生物显示出完全的非对映选择性，5)铜酸盐共轭加成-不饱和酰胺也具有绝对的非对映选择性，6)产生主要立体异构体的反应发生在其Z-/s-顺式构象的4-取代基相反的非对映面，7)由恶唑烷酰胺衍生的Z-烯醇酸锂进行高度的非对映选择性烷基化。8)使用这些Z-烯醇酸锂供体的Michael加成物也具有高度的非对映选择性，9)Z-/s-顺式构象再次参与这些反应，10)这些手性助剂对不对称醛醇反应有效，11)因此，2,2-二取代的oxazolidines不仅在与亲核试剂（如α， β -不饱和酰胺衍生物）的反应中，而且在与亲电试剂（如Z-烯醇酸锂）的反应中都是优秀的手性控制助剂。

The 2,2-disubstituted oxazolidines bearing a chiral center at 4-position act as effective chiral auxiliaries with respect to the following points : 1) They are readily available in optically pure form from naturally occurring alpha-amino acids, 2) their alpha, beta-unsaturated amide derivatives are stabilized in Z-/s-cis conformers so that the unsaturated reaction cite is located close to the 4-shielding substituent, 3) such conformational stability is confirmed by the dynamic ^1H NMR spectra, 4) a nitrile oxide cycloaddition to the alpha, beta-unsaturated amide derivatives of 2,2-disubstituted oxazolidines shows the exclusive diastereofacial selectivity, 5) a cuprate conjugate addition to the alpha, beta-unsaturated amides is also absolutely diastereoselective, 6) the reactions affording the major stereoisomers occur at the diastereofaces opposite to the 4-substituent in their Z-/s-cis conformers, 7) the lithium Z-enolates derived from the oxazolidine amides undergo highly diastereoselective alkylations, 8) Michael additions using these lithium Z-enolate donors are also highly diastereoselective, 9) Z-/s-cis conformers again participate in these reactions, 10) these chiral auxiliaries are effective for asymmetric aldol reactions, 11) as a result, the 2,2-disubstituted oxazolidines act as excellent chirality-controlling auxiliaries in the reactions not only with nucleophiles (as alpha, beta-unsatutated amide derivatives) but also with electrophiles (as lithium Z-enolates).