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首页> 外文期刊>Chemistry: A European journal >Hydrogen-bond-directed catalysis: Faster, regioselective and cleaner Heck arylation of electron-rich olefins in alcohols
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Hydrogen-bond-directed catalysis: Faster, regioselective and cleaner Heck arylation of electron-rich olefins in alcohols

机译：氢键导向催化：更快，区域选择性和更清洁醇中富电子烯烃的Heck芳基化

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摘要

A general method for the regioselective Heck reaction of electron-rich olefins is presented. Fast, highly regioselective Pd-catalysed alpha-arylation of electron-rich olefins, vinyl ethers (1a-d), hydroxyl, vinyl ethers (1e,f), enamides (1g,h) and a substituted vinyl ether (1i) has been accomplished with a diverse range of aryl bromides (2a-r), for the first time, in cheap, green and easily available alcohols with no need for any halide scavengers or salt additives. The reaction proceeds with high efficiency, leading exclusively to the a-products, in 2-propanol and particularly in ethylene glycol. In the latter, the arylation can be catalysed at a palladium loading of 0.1 mol% and finish in as short a time as 0.5 h. The remarkable performance of the alcohol solvents in promoting a regiocontrol is attributed to their hydrogen-bond-donating capability, which is believed to facilitate the dissociation of halide anions from Pd-II, and hence, the generation of a key ionic Pd-II-olefin intermediate responsible for the alpha product. This belief is further strengthened by the study of a benchmark arylation reaction in 21 different solvents. The study revealed that exclusive alpha-regioselective arylation takes place in almost all of the protic solvents, and there is a rough correlation between the alpha-arylation rates and the solvent parameter E-T(N). The method is simpler, cleaner and more general than those established thus far.
机译：提出了一种富电子烯烃的区域选择性Heck反应的一般方法。快速，高度区域选择性Pd催化的富电子烯烃，乙烯基醚（1a-d），羟基，乙烯基醚（1e，f），酰胺（1g，h）和取代的乙烯基醚（1i）的α-芳基化反应首次使用廉价，绿色和易得的醇，使用多种芳族溴化物（2a-r），而无需使用任何卤化物清除剂或盐添加剂。反应在2-丙醇中，特别是在乙二醇中以高效率进行，仅产生α-产物。在后者中，可以在钯负载量为0.1 mol％的条件下催化芳基化反应，并在短至0.5 h的时间内完成。醇类溶剂在促进区域控制方面的卓越性能归因于其氢键给体能力，据信这有助于卤化物阴离子从Pd-II上解离，因此可生成关键的离子性Pd-II-负责α产物的烯烃中间体。通过在21种不同溶剂中进行基准芳基化反应的研究，进一步增强了这一信念。研究表明，几乎所有质子溶剂都发生排他性的α-区域选择性芳基化反应，并且α-芳基化率与溶剂参数E-T（N）之间存在粗略的相关性。该方法比迄今建立的方法更简单，更清洁且更通用。

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