Stereoselective carbonyl-olefination via organosilicon compounds
Stereoselective carbonyl-olefination via organosilicon compounds
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通过有机硅化合物进行立体选择性羰基烯化
DOI：
10.1021/ja00408a049
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发表时间：
1981
影响因子：
15
通讯作者：
H. Yamamoto
中科院分区：
文献类型：
--
作者：
Y. Yamakado;M. Ishiguro;N. Ikeda;H. Yamamoto
由于α 8-氧代三烷基甲硅烷基衍生物的顺式消除已被充分确立，7对所观察到的立体选择性的解释必须归因于α-甲硅烷基碳负离子与羰基化合物的非对映选择性加成（方案I）。考虑到反应通过周环过程进行的合理假设，8可以分析可变空间参数的影响，以确定它们对非对映异构体过渡态的相对形成热的影响。因此，对于丙二烯基阴离子4、9，人们可以预期，通过使R R ′ 3Si空间参数最大化，过渡态T2可能相对于T1不稳定。为了在动力学控制的缩合过程中实现更大的立体化学调节，我们研究了这些反应中的反离子10 * 和空间位阻效应。因此，通过将1当量溴化镁的乙醚溶液加入到4a中制备的丙二烯基镁试剂4 b与己醛反应，以更高的立体选择性（Z/E= 7：1）得到烯炔3。通过改变两个配位体（Li），最终在Z异构体的形成中获得了良好的非对映选择性
Since the syn elimination of the¡ 8-oxido trialkylsilyl derivative is well established, 7 an explanation for the observed stereoselectivity must be attributed to the diastereoselective addition of the a-silyl carbanion to the carbonyl compound (Scheme I). Given the reasonable postulate that the reaction proceeds via a pericyclic process, 8 the influence of variable steric parameters may be an-alyzed to determine their effects upon the relative heats of for-mation of diastereoisomeric transition states. Thus, for the allenyl anion 4, 9 one might anticipate that the transition stateT2 might be destabilized relative to Tj by maximizing theR R'3Si steric parameter. To achieve greater stereochemical regulation in the kinetically controlledcondensation process, we have studied the counterion10* and steric effects conferred upon these reactions. Thus, the allenylmagnesium reagent 4b, prepared by the addition of 1 equiv of magnesium bromide in ether to 4a, reacts with hexanal to give the enyne 3 with higher stereoselectivity (Z/E= 7: 1). Excellent diastereoselection was finally attained in the formation of the Z isomer by changing both the counterion (Li