Chemoselective Pd-Catalyzed Oxidation of Polyols: Synthetic Scope and Mechanistic Studies
Chemoselective Pd-Catalyzed Oxidation of Polyols: Synthetic Scope and Mechanistic Studies
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DOI：
10.1021/ja4008694
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发表时间：
2013-05-22
影响因子：
15
通讯作者：
Waymouth, Robert M.
中科院分区：
文献类型：
--
作者：
Chung, Kevin;Banik, Steven M.;Waymouth, Robert M.
在温和的反应条件下，未保护的邻位多元醇与 [(neocuproine)Pd- (OAc)](2) (OTf)(2) (1) (neocuproine = 2,9-dimethy1-1,10-phenanthroline) 的区域和化学选择性氧化很容易发生，生成 α-羟基酮。邻位二醇的氧化比伯醇和仲醇的氧化更快且更具选择性；邻位1,2-二醇选择性地氧化为羟基酮，而伯醇优先于仲醇被氧化。 1,5-二醇的氧化内酯化产生环内酯。在 10 g 规模的氧化反应中，可以使用低至 0.12 mol% 的催化剂负载。该催化剂体系的精细选择性在多元醇 (S,S)-1,2,3,4-四羟基丁烷 [(S,S)-苏糖醇] 到 (S)-赤藓酮糖的化学选择性和立体定向氧化中显而易见。机理、动力学和理论研究表明，伯醇和仲醇的氧化速率规律与二醇的不同。密度泛函理论计算支持以下结论：β-氢化物消除产生羟基酮是邻二醇氧化的产物决定性，而对于伯醇和仲醇，有利于伯醇的预平衡是产物决定性。原位解吸电喷雾电离质谱（DESI-MS）揭示了所提出的催化循环中的几个关键中间体。
The regio- and chemoselective oxidation of unprotected vicinal polyols with [(neocuproine)Pd- (OAc)](2) (OTf)(2) (1) (neocuproine = 2,9-dimethy1-1,10-phenanthroline) occurs readily under mild reaction conditions to generate alpha-hydroxy ketones. The oxidation of vicinal diols is both faster and more selective than the oxidation of primary and secondary alcohols; vicinal 1,2-diols are oxidized selectively to hydroxy ketones, whereas primary alcohols are oxidized in preference to secondary alcohols. Oxidative lactonization of 1,5-diols yields cyclic lactones. Catalyst loadings as low as 0.12 mol % in oxidation reactions on a 10 g scale can be used. The exquisite selectivity of this catalyst system is evident in the chemoselective and stereospecific oxidation of the polyol (S,S)-1,2,3,4-tetrahydroxybutane [(S,S)-threitol] to (S)-erythrulose. Mechanistic, kinetic, and theoretical studies revealed that the rate laws for the oxidation of primary and secondary alcohols differ from those of diols. Density functional theory calculations support the conclusion that beta-hydride elimination to give hydroxy ketones is product-determining for the oxidation of vicinal diols, whereas for primary and secondary alcohols, pre-equilibria favoring primary alkcaides are product-determining. In situ desorption electrospray ionization mass spectrometry (DESI-MS) revealed several key intermediates in the proposed catalytic cycle.