。在此,我们报告了通过前所未有的苯鎓离子进行阳离子[1,5]-芳基迁移反应的第一个例子的发现和发展。该反应不需要任何酸、碱、过渡金属催化剂或促进剂,而是由水活化的 NXS 试剂促进。它提供了高度非对映选择性和快速获得具有医学和生物学意义的四取代烯烃(烯丙醇)。 2-氧杂螺[5.5]十一烷-9-酮的分离有力地支持了在这种新颖的阳离子[1,5]-芳基迁移过程中,异碳以及苯鎓离子的参与。该方法对于各种炔丙基苄基醚具有高度的耐受性,从而选择性地构建结构不同的单卤代三碳取代烯烃库。通过以立体定向方式将两种异构碘代烯烃转化为他莫昔芬各自的 E 和 Z 异构体,也证明了合成应用。
Expanded Substrate Scope and Improved Reactivity of Ether-Forming Cross-Coupling Reactions of Organotrifluoroborates and Acetals
摘要:
Mixed acetals and organotrifluoroborates undergo BF3 center dot OEt2-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 BF3 center dot OEt2-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 degrees 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.
Synthesis of Dialkyl Ethers from Organotrifluoroborates and Acetals
作者:T. Andrew Mitchell、Jeffrey W. Bode
DOI:10.1021/ja906514s
日期:2009.12.23
The formation of ethers by C-O bond formation under harsh basic or acidic conditions is an entrenched synthetic disconnection in organic chemistry. We report a strategic alternative that involves the BF(3).OEt(2)-promoted coupling of stable, easily prepared acetals with widely available potassium aryl-, alkenyl-, and alkynyltrifluoroborates. This fast, operationally simple process offers straightforward
在苛刻的碱性或酸性条件下通过 CO 键形成形成醚是有机化学中根深蒂固的合成断开。我们报告了一种战略替代方案,涉及 BF(3).OEt(2) 促进的稳定、易于制备的缩醛与广泛可用的芳基-、烯基-和炔基三氟硼酸钾的偶联。这种快速、操作简单的过程提供了直接获得二烷基醚的途径,其中许多使用经典方法难以制备。使用 MOM 保护的醇和缩醛保护的醛可以形成醚,而无需求助于保护基操作或强碱。