SHAPE-SELECTIVE AND ASYMMETRIC CYCLOPROPANATION OF ALKENES CATALYZED BY RHODIUM PORPHYRINS
SHAPE-SELECTIVE AND ASYMMETRIC CYCLOPROPANATION OF ALKENES CATALYZED BY RHODIUM PORPHYRINS
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DOI：
10.1021/om00038a023
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发表时间：
1992-02-01
期刊：
影响因子：
2.8
通讯作者：
KODADEK, T
中科院分区：
文献类型：
--
作者：
MAXWELL, JL;OMALLEY, S;KODADEK, T
铑卟啉用重氮酯催化简单烯烃环丙化反应。催化选择性环丙化反应的功能化催化剂可能用于有机合成，特别是因为卟啉催化剂通常以syn环丙酯为主要产物。在本报告中，我们研究了工程形状选择性和不对称诱导进入该系统的可能性。我们证明了一种旋光性大环的碘碘衍生物，即“手性壁”卟啉，确实介导了前手性烯烃的对映选择性环丙烷化。观察到10-60%的对映体过量。此外，对受阻（RhTMPI）和无受阻（RhTTPI）简单卟啉的底物选择性进行了评价。在这两种情况下，单取代、二取代和三取代的脂肪烯烃以几乎相等的速率进行反应，但四取代的烯烃环丙烷化很差，特别是当使用拥挤的催化剂时。对于体积较大的芳烃，观察到极高的顺式/反式底物选择性。这些观察结果导致了假定的金属卡宾和烯烃之间相互作用的几何模型，使所研究的许多底物的相对反应性合理化。本文还讨论了这些结果与合理设计选择性更强的不对称催化剂的相关性。
Rhodium porphyrins catalyze the cyclopropanation of simple alkenes by diazo esters. Functionalized catalysts that mediate selective cyclopropanation reactions might be of use in organic synthesis, particularly since the porphyrin catalysts generally provide syn cyclopropyl esters as the major product. In this report we examine the possibility of engineering shape selectivity and asymmetric induction into this system. We show that the iodorhodium derivative of an optically active macrocycle, the ''chiral wall'' porphyrin, does mediate the enantioselective cyclopropanation of prochiral olefins. Enantiomeric excesses of 10-60% are observed. In addition, the substrate selectivities of hindered (RhTMPI) and unhindered (RhTTPI) simple porphyrins were assessed. In both cases, mono-, di-, and trisubstituted aliphatic olefins undergo reaction at nearly equivalent rates but tetrasubstituted alkenes are cyclopropanated poorly, especially when the crowded catalyst is employed. In the case of bulkier aromatic alkenes, extremely high cis/trans substrate selectivity is observed. These observations have led to a model for the geometry of interaction between the putative metallocarbene and the alkene that rationalizes the relative reactivity of the many substrates investigated. The relevance of these results to the rational design of more selective asymmetric catalysts is also discussed.