Atom-economical preparation of aryl- and heteroaryl-lanthanum reagents by directed ortho-metalation by using tmp3[La].
Atom-economical preparation of aryl- and heteroaryl-lanthanum reagents by directed ortho-metalation by using tmp3[La].
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DOI：
10.1002/chem.200903157
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发表时间：
2010-03
期刊：
影响因子：
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通讯作者：
S. Wunderlich;P. Knochel
中科院分区：
文献类型：
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作者：
S. Wunderlich;P. Knochel
芳香族化合物和杂芳香族化合物的邻位金属化是这些环系功能化的有力方法。虽然锂碱和几种酸盐碱允许制备各种邻位金属化产物，但仍然需要更多的化学选择性碱。最近，我们报道了tmpMgCl·LiCl（1; tmp = 2，2，6，6-四甲基哌啶基）或tmpLi与金属氯化物的反应，如ZnCl 2，[7] AlCl 3，[8] MnCl 2·2LiCl，[9] FeCl 2·2LiCl或FeCl 3 [10]，提供了高度化学选择性的碱，可以耐受一系列官能团。这些碱中MgCl 2和LiCl的存在确保了在THF中的良好溶解性和高动力学碱度（比较tmp 2 Zn·2 MgCl 2·2LiCl和tmpZnCl·LiCl）。[7d]有机镧衍生物是相对廉价的低毒性有机金属中间体。它们通常通过从锂或镁试剂开始的金属转移反应来制备，如Imamoto所开创的。已经报道了几种镧酰胺，主要用于氢胺化反应的性能或用于结构研究。在此，我们希望报道一种新的碱，即tmp 3La·3 MgCl 2·5LiCl（2，为了清楚起见，缩写为tmp 3 [La]）。tmp 3 [La]（2）与类型3的官能化芳烃和杂芳烃的反应允许在温和条件下方便地获得类型4的官能化芳基和杂芳基衍生物。这些不饱和镧衍生物显示出独特的反应性模式，并与各种亲电试剂（5）反应，产生一系列类型6的多官能产物。新碱2是由tmpMgCl·LiCl（1; 3.0equiv）与可溶于THF的配合物LaCl_3·2LiCl [15]在THF中反应12 h而制得的。得到的深棕色溶液（在THF中0.33m;通过滴定测定产率为95%）在氩气下稳定至少2个月而不分解（方案1）。
The ortho-metalation of aromatics and heteroaromatics is a powerful method for the functionalization of these ring systems. Although lithium bases and several ate-bases allow the preparation of various ortho-metalated products, there is still a need for more chemoselective bases. Recently, we reported that the reaction of tmpMgCl·LiCl (1; tmp = 2,2,6,6-tetramethylpiperidyl) or tmpLi with metallic chlorides, such as ZnCl2, [7] AlCl3, [8] MnCl2·2LiCl, [9] FeCl2·2LiCl, or FeCl3 [10] provides highly chemoselective bases that tolerate a range of functional groups. The presence of MgCl2 and LiCl in these bases ensures good solubility in THF and a high kinetic basicity (compare tmp2Zn·2MgCl2·2LiCl with tmpZnCl·LiCl). [7d] Organolanthanum derivatives are relatively inexpensive organometallic intermediates of low toxicity. They are usually prepared by transmetalation reactions starting from lithium or magnesium reagents as has been pioneered by Imamoto. Several lanthanum amides have been reported, mainly for the performance of hydroamination reactions or for structural studies. Herein, we wish to report a new base, that is, tmp3La·3MgCl2·5LiCl (2, abbreviated, for the sake of clarity, to tmp3[La]). The reaction of tmp3[La] (2) with functionalized arenes and heteroarenes of type 3 allows an expedient access to functionalized aryl and heteroaryl derivatives of type 4 under mild conditions. These unsaturated lanthanum derivatives display a unique reactivity pattern and react with various electrophiles (5) producing a range of polyfunctional products of type 6. The new base 2 is readily prepared by the reaction of tmpMgCl·LiCl (1; 3.0 equiv) with the THF soluble complex LaCl3·2LiCl [15] in THF for 12 h. The resulting dark brown solution (0.33m in THF; 95 % yield as determined by titration) is stable under argon for at least 2 months without decomposition (Scheme 1).