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Expanded Substrate Scope and Improved Reactivity of Ether-Forming Cross-Coupling Reactions of Organotrifluoroborates and Acetals
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2011-09-07 , DOI: 10.1021/ja205174c Cam-Van T Vo 1 , T Andrew Mitchell , Jeffrey W Bode
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2011-09-07 , DOI: 10.1021/ja205174c Cam-Van T Vo 1 , T Andrew Mitchell , Jeffrey W Bode
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Mixed acetals and organotrifluoroborates undergo BF(3)·OEt(2)-promoted cross-couplings to give dialkyl ethers under simple, mild conditions. A survey of reaction partners identified a hydroxamate leaving group that improves the regioselectivity and product yield in the BF(3)·OEt(2)-promoted coupling reaction of mixed acetals and potassium alkynyl-, alkenyl-, aryl- and heteroaryltrifluoroborates to access substituted dialkyl ethers. This leaving group enables the reaction to proceed rapidly under mild conditions (0 °C, 5-60 min) and permits reactions with electron-deficient potassium aryltrifluoroborates that are less reactive with other acetal substrates. A study of the reaction mechanism and characterization of key intermediates by NMR spectroscopy and X-ray crystallography identified a role for the hydroxamate moiety as a reversible leaving group that serves to stabilize the key oxocarbenium intermediate and the need for a slight excess of organodifluoroborane to serve as a catalyst. A secondary role for the boron nucleophile as an activating ligand was also considered. These studies provide the basis for a general class of reagents that lead to dialkyl ethers by a simple, predictable cross-coupling reaction.
中文翻译：
有机三氟硼酸盐和乙缩醛形成醚的交叉偶联反应扩大了底物范围并提高了反应性
混合缩醛和有机三氟硼酸盐经过 BF(3)·OEt(2) 促进的交叉偶联，在简单、温和的条件下得到二烷基醚。对反应伙伴的调查确定了异羟肟酸酯离去基团，该基团可提高混合缩醛和炔基-、烯基-、芳基-和杂芳基三氟硼酸钾在 BF(3)·OEt(2) 促进的偶联反应中的区域选择性和产物收率，以获取取代的二烷基醚。该离去基团使反应能够在温和条件下（0 °C，5-60 分钟）快速进行，并允许与缺电子的芳基三氟硼酸钾反应，后者与其他缩醛底物的反应性较低。通过 NMR 光谱和 X 射线晶体学对关键中间体的反应机理和表征进行的研究确定了异羟肟酸酯部分作为可逆离去基团的作用，用于稳定关键的氧代碳鎓中间体，并且需要略微过量的有机二氟硼烷。作为催化剂。还考虑了硼亲核试剂作为活化配体的次要作用。这些研究为通过简单、可预测的交叉偶联反应生成二烷基醚的一类通用试剂提供了基础。
更新日期：2011-09-07
中文翻译：
有机三氟硼酸盐和乙缩醛形成醚的交叉偶联反应扩大了底物范围并提高了反应性
混合缩醛和有机三氟硼酸盐经过 BF(3)·OEt(2) 促进的交叉偶联，在简单、温和的条件下得到二烷基醚。对反应伙伴的调查确定了异羟肟酸酯离去基团，该基团可提高混合缩醛和炔基-、烯基-、芳基-和杂芳基三氟硼酸钾在 BF(3)·OEt(2) 促进的偶联反应中的区域选择性和产物收率，以获取取代的二烷基醚。该离去基团使反应能够在温和条件下（0 °C，5-60 分钟）快速进行，并允许与缺电子的芳基三氟硼酸钾反应，后者与其他缩醛底物的反应性较低。通过 NMR 光谱和 X 射线晶体学对关键中间体的反应机理和表征进行的研究确定了异羟肟酸酯部分作为可逆离去基团的作用，用于稳定关键的氧代碳鎓中间体，并且需要略微过量的有机二氟硼烷。作为催化剂。还考虑了硼亲核试剂作为活化配体的次要作用。这些研究为通过简单、可预测的交叉偶联反应生成二烷基醚的一类通用试剂提供了基础。
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