Unique reactivities of new highly coordinated ate complexes of organozinc derivatives
Unique reactivities of new highly coordinated ate complexes of organozinc derivatives
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DOI：
10.1021/ja961320e
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发表时间：
1996-09-11
影响因子：
15
通讯作者：
Sakamoto, T
中科院分区：
文献类型：
--
作者：
Uchiyama, M;Koike, M;Sakamoto, T
有机锌试剂在有机合成中有着广泛的应用。有机锌衍生物的最重要的类别是有机锌卤化物和二有机锌，并且这些已经通过锌金属与有机卤化物的氧化加成反应或通过有机锂或有机镁化合物与氯化锌的金属转移反应制备。三有机锌酸酯作为一种新型的合成试剂，可以方便地将各种有机基团以1，4-方式转移到R，β-不饱和酮上。2据报道，三烷基锌酸锂也可用作芳族卤化物或乙烯基卤化物的金属化试剂。3三烷基锌酸锂中锌原子的外壳充满了16个电子，并且有一个额外的配体配位的空间，以形成有利的18电子状态。有一些关于四烷基锌酸盐的报道4和配合物的X-射线研究表明，在四烷基锌酸盐的晶体结构中，存在关于锌原子的四面体排列。5然而，四烷基锌酸盐的反应性尚未得到很好的研究。这些配合物独特的四面体形式使我们研究了这些四烷基有机锌酸酯和相关的改性有机锌酸酯的反应性。有机锌酸盐的~ 1H-NMR研究表明，这些高度配位的锌酸盐与三甲基锌酸锂之间的差异。比较这些试剂的反应性的研究揭示了不同的区域选择性环氧化物开放和不同的反应性对卤素-金属交换。这些结果支持了这些高配位锌酸盐在结构和反应活性上应区别于普通的三烷基锌酸锂的观点。首先，研究了高配位锌酸盐的制备，并对锌酸盐的1H-NMR谱进行了测定，初步估算了锌酸盐溶液的组成。四甲基锌酸二锂通过氯化锌与4当量甲基锂在THF中的反应使用改进的报道的方法制备。4a在Me 3 ZnLi（-1.08ppm）和MeLi（-1.96ppm）的信号之间的中间观察到Me 4-ZnLi 2在THF中的甲基信号（-1.44ppm）为尖锐的单峰。从Me 3 ZnLi的值的高场位移被认为指示锌酸盐的更多阴离子特征。在-78 ℃下的测量给出了非常相似的结果，每个信号都有轻微的高场偏移。再向Me 4 ZnLi 2溶液中加入一当量MeLi，在-20 ℃下在-1.49ppm处产生宽的单重峰信号，该信号在-78 ℃下分离成两个信号，分别对应于MeLi的信号和Me 4 ZnLi 2的信号.将1当量的Me 3SiCN或Me 3SiNCS添加到Me 4 ZnLi 2溶液中应得到甲基被CN或SCN配体取代的锌酸盐。正如我们所预期的，四甲基锌酸盐与Me 3SiCN和Me 3-SiNCS的反应得到新的锌酸盐，Me 3 Zn（CN）Li 2（3）和Me 3 Zn-（SCN）Li 2（4a），其中甲基信号被观察为尖锐的单线态（对于3为-1.20ppm，对于4a为-1.23ppm）。6a作为制备CN-或SCN-连接的锌酸盐的替代方法，检查Zn（CN）2或Zn（SCN）2与3当量甲基锂的反应。从早期的1H-NMR研究中，Zn（CN）2与MeLi的反应是缓慢的，并且没有观察到锌酸盐的形成。6 b，而Zn（SCN）2与MeLi的反应得到类似于4a的锌酸盐（~ 1.31ppm）（表1）。这些结果表明，除了Zn（CN）2与MeLi反应外，还形成了不同种类的锌酸盐，并且这些高度配位的锌酸盐比Me 3 ZnLi更具有阴离子性，这促使我们研究这些锌酸盐。
Organozinc reagents have been extensively used in organic synthesis. 1 The most important classes of organozinc derivatives have been organozinc halides and diorganozincs, and these have been prepared either by oxidative addition reaction of zinc metal to organic halides or by transmetalation reaction of organolithio or organomagnesio compounds with zinc chloride. As a new type of synthetic reagent, triorganozincates were reported to be convenient and synthetically useful for transferring various organic moieties to R, β-unsaturated ketones in a 1, 4-fashion. 2 Lithium trialkylzincates were also reported to be useful as metalating reagents of aromatic halides or vinyl halides. 3 The outer shell of the zinc atom in a lithium trialkylzincate is filled with 16 electrons, and there is a room for an additional ligand to coordinate to form a favorable 18-electron state. There are some reports on tetraalkylzincates4 and X-ray studies of the complexes which have disclosed that in the crystal structure of tetraalkylzincates there is a tetrahedral arrangement about the zinc atom. 5 However the reactivities of tetraalkylzincates have not been well studied. The unique tetrahedral form of these complexes made us study the reactivity of these tetraalkylorganozincates and related modified organozincates. The 1H-NMR study of organozincates indicated the difference between these highly coordinated zincates and lithium trimethylzincate. Studies to compared the reactivity of these reagents disclosed a different regioselectivity for epoxide opening and a different reactivity toward halogen-metal exchange. These results support that these highly coordinated zincates should be distinguished from ordinary lithium trialkylzincates in structure and reactivity.First, preparation of highly coordinated zincates were investigated, and 1H-NMR spectra of the zincates were measured for the preliminary estimation of the component of the zincate solution. Dilithium tetramethylzincate was prepared by the reaction of zinc chloride with 4 equiv of methyllithium in THF using the modified reported procedure. 4a The methyl signal of Me4-ZnLi2 in THF (-1.44 ppm) was observed midway as a sharp singlet between the signals of Me3ZnLi (-1.08 ppm) and MeLi (-1.96 ppm). High-field shift from the value of Me3ZnLi is considered to indicate the more anionic character of the zincates. Measurement at-78 C gave very similar results with a slight high-field shift of each signal. Addition of one more equivalent of MeLi to the Me4ZnLi2 solution resulted in a broad singlet signal at-1.49 ppm at-20 C which separated at-78 C into two signals corresponding to the signals of MeLi and those of Me4ZnLi2. Addition of 1 equiv of Me3SiCN or Me3SiNCS to the Me4ZnLi2 solution should give the zincates with methyl group replacement by the CN or SCN ligand. As we expected, the reaction of the tetramethylzincate with Me3SiCN and Me3-SiNCS gave the new zincates, Me3Zn (CN) Li2 (3) and Me3Zn-(SCN) Li2 (4a), of which methyl signals were observed as sharp singlets (-1.20 ppm for 3 and-1.23 ppm for 4a). 6a As an alternative way to prepare CN-or SCN-ligated zincates, the reaction of Zn (CN) 2 or Zn (SCN) 2 with 3 equiv of methyllithium was examined. From the preliminarly 1H-NMR study, the reaction of Zn (CN) 2 with MeLi is sluggish and no formation of a zincate was observed, 6b while the reaction of Zn (SCN) 2 with MeLi gave a zincate (-1.31 ppm) similar to 4a (Table 1). These results indicate that the different species of zincates are formed except for the reaction of Zn (CN) 2 with MeLi, and the more anionic character of these highly coordinated zincates than that of Me3ZnLi encouraged us to investigate the …