TITANIUM-INDUCED REDUCTIVE COUPLING OF CARBONYLS TO OLEFINS
TITANIUM-INDUCED REDUCTIVE COUPLING OF CARBONYLS TO OLEFINS
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DOI：
10.1021/jo00411a002
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发表时间：
1978-01-01
影响因子：
3.6
通讯作者：
KREPSKI, LR
中科院分区：
文献类型：
--
作者：
MCMURRY, JE;FLEMING, MP;KREPSKI, LR
通过用钾或锂还原TiCl 3而以精细分散的形式产生的活性钛金属将酮和醛还原偶联成烯烃。虽然当两个相同的羰基偶联到对称产物时分子间偶联效果最好，但在某些情况下也可以进行不对称偶联。与另一个合作伙伴的二芳基酮的不对称耦合是特别有效的，并提出了一种机制来解释这一点。分子内二羰基偶联形成环也是可能的，并且TiCL/Zn-Cu的组合效果最好。以高产率制备尺寸为4-16和22的环。用扫描电子显微镜研究了活性钛金属的性质，并提出了解释所有观察结果的机理建议。目前认为偶联反应发生在活性钛颗粒的表面。最近，三个独立的研究小组独立地观察到低价钛试剂（TiCl 4/Zn，1 TiCl 3/Mg，2 TiCl 3/LiAlH 43）将酮和醛还原二聚为烯烃。据报道，这些试剂体系中的两种仅对芳基酮有效，而我们的TiCl 3/LiAlH 4试剂在芳基和烷基的情况下都给出了优异的产率。[3]随后，许多研究小组使用我们的方法制备了各种有趣的烯烃，[4-9]但是，正如我们所报道的，[10] TiCl 3/LiAlH 4试剂根据所用试剂的确切批次给出了多变的结果。
Active titanium metal, produced in a finely divided form by reduction of TiCl3 with either potassium or lithium, will reductively couple ketones and aldehydes to olefins. Although the intermolecular coupling works best when two identical carbonyls are coupled to a symmetrical product, unsymmetrical couplings can also be carried out in certain cases. The unsymmetrical coupling of a diaryl ketone with another partner is particularly efficient, and a mechanism to account for this is proposed. Intramolecular dicarbonyl coupling to form rings is also possible, and the combination TiCL/Zn-Cu works best. Rings of size 4-16 and 22 are prepared in high yield. The nature of the active titanium metal is studied by scanning electron microscopy, and a mechanistic proposal accounting for all observed results is presented. It is believed that the coupling reaction occurs on the surface of the active titanium par-ticle.Recently, three separate research groups independently observed that low-valent titanium reagents (TiCU/Zn, 1 TiCl3/Mg, 2 TiCl3/LiAlH43) would reductively dimerize ketones and aldehydes to olefins^ Twoof these reagent systems1’2 were reported to be effective only for aryl ketones, while our TiCls/LiAlH4 reagent gave excellent yields in both aryl and alkyl cases. 3 Subsequently, a number of research groups used our method to prepare a variety of interesting olefins, 4-9 but, as we have reported, 10 the TiCl3/LiAlH4 reagent gives capri-cious results depending on the exact batches of reagents used.