Chiral nonracemic alpha-alkylidene and alpha-silylidene cyclopentenones from chiral allenes using an intramolecular allenic Pauson-Khand-type cycloaddition.
Chiral nonracemic alpha-alkylidene and alpha-silylidene cyclopentenones from chiral allenes using an intramolecular allenic Pauson-Khand-type cycloaddition.
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使用分子内丙二烯 Pauson-Khand 型环加成反应从手性丙二烯得到手性非外消旋 α-亚烷基和 α-甲硅烷基环戊烯酮。
DOI：
10.1021/jo016305t
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发表时间：
2002
期刊：
影响因子：
--
通讯作者：
Wan,Honghe
中科院分区：
文献类型：
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作者：
Brummond,KayM;Kerekes,AngelaD;Wan,Honghe
我们已经成功地实现了手性从手性非外消旋联烯到α-亚烷基和α-硅亚基环戊酮的转移。在钼的作用下，烯丙烯末端含有硅基的化合物表现出良好的表面选择性，但(E)-亚甲基环戊酮在纯化后会发生异构化为(Z)-亚甲基环戊酮。或者，烯丙烯末端的烷基以中等的选择性进行环加成反应，但在酸性条件下产生(Z)-亚烷基环戊烯酮异构化为(E)-亚烷基环戊烯酮的产物。因此，作为这种异构化的结果，观察到两种产品中的一种的对映体过量的侵蚀。首次分离了(η6-芳烃)钼三羰基络合物，首次证明该络合物最有可能是钼催化反应中的活性络合物。通过增加芳烃部分的尺寸来增加表面选择性的尝试导致了以牺牲产量为代价的选择性的边际增加。基于这些结果，我们得出结论，为了获得综合有用的立体控制水平，有必要改变非外消旋α-亚烷基环戊酮的制备方法。
We have successfully effected a transfer of chirality from a chiral nonracemic allene to an α-alkylidene and an α-silylidene cyclopentenone. The molybdenum-mediated examples possessing a silyl group on the terminus of the allene show good facial selectivities, but isomerization of the (E)-silylidene cyclopentenone to the (Z)-silylidene cyclopentenone occurs upon purification of these products. Alternatively, an alkyl group on the terminus of the allene undergoes cycloaddition with moderate selectivities but gives products that undergo an isomerization of the (Z)-alkylidene cyclopentenone to the (E)-alkylidene cyclopentenone when exposed to acidic conditions. Thus, erosion of the enantiomeric excesses is observed for one of the two products as a result of this isomerization. The allenic Pauson−Khand-type cycloaddition has also been effected by first isolation the (η6-arene)molybdenum tricarbonyl complex, demonstrating for the first time that this is most likely the active complex in the molybdenum-mediated reactions. Attempts to increase the facial selectivity by increasing the size of the arene moiety resulted in a marginal increase in the selectivity at the expense of the yield. Based upon these results, we have concluded that altering the approach for the preparation of nonracemic α-alkylidene cyclopentenones is necessary in order to obtain synthetically useful levels of stereocontrol.