Thiol ester-boronic acid coupling. A mechanistically unprecedented and general ketone synthesis
Thiol ester-boronic acid coupling. A mechanistically unprecedented and general ketone synthesis
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DOI：
10.1021/ja005613q
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发表时间：
2000-11-15
影响因子：
15
通讯作者：
Srogl, J
中科院分区：
文献类型：
--
作者：
Liebeskind, LS;Srogl, J
在各种生物化学转化中，在大量氧和氮杂原子的存在下，实现了稳定的碳-硫键的高度区别性活化。1，2硬-软酸碱的原理，3例如，在硬环境中软基质与软活化剂的选择性相互作用，反之亦然，有助于合理化自然界使用生物相关的亲硫金属，如镍，以实现水中碳-硫键的选择性断开。在这种CS活化模式中隐含的是生物系统防止从嗜硫金属形成难熔金属硫醇盐的能力。鉴于上述考虑，新的基于实验室的合成方法，涉及金属催化的碳-硫键断裂，并导致在非常温和的条件下形成新的碳-碳键应该是可行的。在以上讨论中隐含的是，有机硫化合物的金属催化转换需要活化在催化活性金属和软硫原子之间形成的稳定键。我们以前已经证明了牺牲ZnII在促进巯基乙酸盐系统的交叉偶联中的重要性，4并且最近描述了使用“烷基化活化”原理的硫醇酯-硼酸交叉偶联。5后者利用了我们先前公开的作为高效交叉偶联配偶体的锍盐。6，7我们现在报道了在严格的非碱性反应条件下，在噻吩-2-羧酸铜（CuTC）9的存在下，硫醇酯8与硼酸发生钯催化偶联生成酮的独特和前所未有的机理（表1，图1）。尽管已知许多合成酮的方法，但没有一种方法是足够通用的，以允许在中性条件下偶联稳定且官能度丰富的反应伴侣。硫羟酸酯到酮的一些转化是已知的;它们在碱性反应条件下进行并且不是通用的。13-18芳酰氯
Highly discriminating activation of a stable carbon-sulfur bond is achieved in the presence of a vast sea of oxygen and nitrogen heteroatoms in various biochemical transformations. 1, 2 The Principle of Hard-Soft Acids and Bases, 3 eg, the selective interaction of a soft substrate with a soft activator in a hard environment and vice versa, helps to rationalize Nature’s use of biologically relevant thiophilic metals such as Ni to achieve selective disconnection of the carbon-sulfur bond in water. Implicit in this mode of CS activation is the capacity of the biological system to prevent the formation of refractory metal thiolates from thiophilic metals.Given the above considerations, new laboratory-based synthetic processes that involve metal-catalyzed carbon-sulfur bond scission and lead to new carbon-carbon bond formation under very mild conditions should be feasible. It is implicit in the discussion above that metal-catalyzed turnover of organosulfur compounds requires activation of the stable bond that forms between a catalytically active metal and the soft sulfur atom. We have previously demonstrated the importance of sacrificial ZnII in facilitating the cross-coupling of thioglycolate systems, 4 and more recently described a thiol ester-boronic acid crosscoupling using the principle of “alkylative activation”. 5 The latter draws on our earlier disclosures of sulfonium salts as highly effective cross-coupling partners. 6, 7 We now report a mechanistically unique and unprecedented Pd-catalyzed coupling of thiol esters8 with boronic acids to give ketones that proceeds in the presence of CuI thiophene-2-carboxylate (CuTC) 9 under strictly nonbasic reaction conditions (Table 1, Chart 1). Although many methods for the synthesis of ketones are known, 10-12 none is sufficiently general to allow the coupling of stable and functionally rich reaction partners under neutral conditions. Some transformations of thiol esters to ketones are known; they proceed under basic reaction conditions and are not general. 13-18 Aroyl chlorides