Metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions
Metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions
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DOI：
10.3891/acta.chem.scand.50-0652
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发表时间：
1996-08-01
期刊：
影响因子：
--
通讯作者：
Jorgensen, KA
中科院分区：
文献类型：
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作者：
Gothelf, KV;Jorgensen, KA
1，3-偶极环加成反应是有机化学中的一个重要反应，因为合成的多用途异恶唑烷具有多达三个连续的手性中心。介绍了金属催化的烷烃与硝酮的不对称1，3-偶极环加成反应的最新进展。提出了N-丙烯酰氧唑烷酮与硝酮之间1，3-偶极环加成反应的新催化方法。在手性TiCl2-TADDOLate催化剂的作用下，1，3-偶极环加成反应具有外选择性和对映体选择性。当配体在催化剂上的配位方式改变为例如镁-Ⅱ-邻菲咯啉催化剂时，1，3-偶极环加成反应具有很高的内选择性。使用手性烯烃在镁-II-邻菲咯啉催化的反应中导致高的或完全的双非对映选择性。在1，3-偶极烯烃与硝酮的环加成反应中，使用手性的Mg-II-双恶唑啉催化剂可以实现高的内向选择性和高达82%的对映选择性。基于对镁(II)络合物催化反应过渡态的一系列半经验量子化学计算，可以解释反应的催化和非对映选择性和对映体选择性过程。将外选择性TiCl2-TADDOLate催化剂中的氯离子配体替换为对甲苯磺酸配体，可进一步提高烯烃与硝酮1，3-偶极环加成反应的对内和对映体选择性，获得90%的非对映选择性和对映体选择性。烯烃与硝酮的1，3-偶极环加成反应的这些方面的发展是基于TiCl2-TADDOLATE-烯烃中间体的分离和表征，这导致了对硝酮接近烯烃的机理的理解。
The 1,3-dipolar cycloaddition reaction is an important reaction in organic chemistry since synthetically versatile isoxazolidines with up to three contiguous chiral centers can be formed. The most recent highlights in metal-catalyzed asymmetric 1,3-dipolar cycloaddition reactions of alkanes with nitrones are described. A new catalytic approach for the 1,3-dipolar cycloaddition reaction between N-acryloyloxazolidinones and nitrones has been developed. By the application of a chiral TiCl2-TADDOLate catalyst this 1,3-dipolar cycloaddition reaction proceeds with both exo- and enantio-selectivity. When the coordination mode of the ligands at the catalyst is changed to, e.g., a Mg-II-phenanthroline catalyst, the 1,3-dipolar cycloaddition reaction proceeds with a high degree of endo-selectivity. Employing a chiral alkene in the Mg-II-phenanthroline-catalyzed reaction leads to high, or complete, double diastereoselectivity. By the use of a chiral Mg-II-bisoxazoline catalyst high endo-selectivity, and up to 82% enantioselectivity in the 1,3-dipolar cycloaddition reaction of alkenes with nitrones can be achieved. On the basis of a series of semiempirical quantum chemical calculations of the transition states for the magnesium(II) complex catalyzed reactions the catalytic and the diastereo- and enantio-selective course of the reactions can be accounted for. The endo- and enantio-selectivity in the 1,3-dipolar cycloaddition reaction of alkenes with nitrones can be further improved by replacement of the chloride ligands in the exo-selective TiCl2-TADDOLate catalyst with tosylato ligands to give diastereo- and enantio-selectivities of >90%. The development of these aspects of the 1,3-dipolar cycloaddition reaction of alkenes with nitrones is based on the isolation and characterisation of a TiCl2-TADDOLate-alkene intermediate which has led to an understanding of the mechanism of the approach of the nitrone to the alkene.