Transition-Metal-Catalyzed Synthesis of Diboranes(4)
Transition-Metal-Catalyzed Synthesis of Diboranes(4)
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DOI：
10.1002/anie.201104854
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发表时间：
2011-01-01
影响因子：
16.6
通讯作者：
Guethlein, Frank
中科院分区：
文献类型：
--
作者：
Braunschweig, Holger;Guethlein, Frank
有机硼烷是以sp2杂化的Br2基团为特征的有机分子。这种Br2片段具有良好的σ碱性和π酸性，使C±B键具有独特的反应活性，这一点已经被有机化学家所利用。在20世纪早期，有机硼烷在有机化学中只是作为羟基的占位符，将C±Br2键氧化成C±OH是合成醇的可靠方法。然而，直到发现了有机硼烷与芳基卤化物的Suzuki-Miyaura交叉偶联后，这种官能团才在有机化学中得到了广泛的应用。[1]这种方法已经发展成为可用于C？C键形成的最通用的合成方法之一，并成为2010年诺贝尔化学奖的主题。对在有机分子中安装Br2基团的方便和经济的方法的需求推动了一段时间对有机硼烷化学的研究。20世纪50年代，Brown和他的同事发展了不饱和有机底物的氢化硼化反应，使有机硼烷化学不再鲜为人知，并将硼添加到有机化学家S的方程式中。[3]很长一段时间以来，简单的氢化硼化反应仍然是合成有机硼化合物的首选方法。在20世纪80年代，Sneddon，Marder和Nçth等人报道了过渡金属催化的氢化硼化反应，从而提供了获得具有替代化学选择性和区域选择性的硼烷产物的途径，以补充经典的氢化硼化反应。此外，不饱和化合物的催化二硼化[5]以及芳烃[6]和烷烃[7]的硼化反应提供了更广泛种类的有机硼酸盐。在许多此类反应中，不可缺少的起始原料是通式(RO)2B±B(OR)2的四烷氧基二硼烷(4)。这类化合物最常用的两种试剂是双(儿茶酚)二硼烷(B2Cat2；1)和双(频二硼酸)二硼烷(B2Pin2；2)，它们目前是由Brotherton于1960年建立的方法合成的，[8]在其间的几十年中经过了多次修改。随后，通过与钠还原偶联生成B2(NMe2)4(3)，与相应的二元醇反应进一步转化为1和2(方案1)，从而形成硼-硼键。
Organoboranes are organic molecules featuring an sp2-hybridised BR2 group. This BR2 fragment, with its welldocumented σ basicity and π acidity, lends the CÀB bond a unique reactivity that has been impressively exploited by organic chemists. In the early 20th century, organoboranes featured in organic chemistry merely as placeholders for hydroxy groups, the oxidation of a CÀBR2 bond to CÀOH being a reliable method for the synthesis of alcohols. However, it was only after the discovery of the Suzuki–Miyaura cross-coupling of organoboranes with aryl halides that this functional group became widely used in organic chemistry.[1] This method has since developed into one of the most versatile synthetic methods available for CÀC bond formation and it was the subject of the Nobel Prize in Chemistry in 2010.[2] Consequently, the need for convenient and economical methods for the installation of the BR2 group in organic molecules has fuelled research into organoborane chemistry for some time.The hydroboration of unsaturated organic substrates developed by Brown and co-workers in the 1950s brought organoborane chemistry out of obscurity and added boron to the organic chemist s repertoire.[3] For a long time, simple hydroboration remained the method of choice for the synthesis of organoboronates. In the 1980s, the groups of Sneddon, Marder, and Nçth reported the transition-metalcatalyzed hydroboration reaction, thus providing access to borane products with alternative chemo-and regioselectivity to complement those prepared by classical hydroboration.[4] Furthermore, catalytic diboration of unsaturated compounds [5] as well as the borylation of arenes [6] and alkanes [7] gave access to a much broader variety of organoboronates. An indispensable starting material in many of these reactions is a tetraalkoxydiborane (4) of the general formula (RO) 2BÀB (OR) 2. The two most commonly used reagents of this class of compounds are bis (catecholato) diborane (B2Cat2; 1) and bis (pinacolato) diborane (B2Pin2; 2), which are currently synthesized by a method established by Brotherton in 1960,[8] which has been modified several times over the intervening decades.[9] Starting from boron tribromide, bromobis (dimethylamino) borane is synthesized in two steps. Subsequently, formation of the boron–boron bond is achieved by reductive coupling with sodium to yield B2 (NMe2) 4 (3), which is further converted into 1 and 2 upon reaction with the corresponding diols (Scheme 1).[9a, d, 10] Alternatively, 1 can be