Plietker Bernd, Niggemann Meike
Organic Chemistry II, Chemistry Faculty, Dortmund University, Otto-Hahn-Str. 6, D-44221 Dortmund, Germany.
J Org Chem. 2005 Mar 18;70(6):2402-5. doi: 10.1021/jo048020x.
[reaction: see text] The catalytic dihydroxylation of olefins represents a unique synthetic tool for the generation of two C,O-bonds with defined relative configuration. Whereas OsO(4) has been established as a very general dihydroxylation catalyst within the past 30 years, the less expensive and toxic isoelectronic RuO(4) has found only limited use for this type of oxygen-transfer reaction. High catalyst loading and undesired side reactions were severe drawbacks in RuO(4)-catalyzed oxidations of C,C-double bonds. Recently, we were able to improve the RuO(4)-catalyzed dihydroxylation by addition of Bronsted acids to the reaction mixture. This protocol proved to be of general applicability, however, certain limitations were observed. To address these problematic functional groups a new Lewis acid accelerated oxidation was developed. The use of only 10 mol % of CeCl(3) allowed a further decrease in the catalyst concentration down to 0.25 mol % while broadening the scope of the reaction. Silyl ethers and nitrogen containing functional groups are now tolerated in this optimized protocol. Furthermore, competing scission reactions are supressed in the presence of Lewis acid allowing longer reaction times and the successful oxidation of electron-deficient tetrasubstituted double bonds that cannot be oxidized using known dihydroxylation protocols.
[反应：见正文]烯烃的催化二羟基化是一种独特的合成工具，用于生成具有确定相对构型的两个碳-氧键。在过去30年里，四氧化锇已被确立为一种非常通用的二羟基化催化剂，而价格较低且毒性较小的等电子体四氧化钌在这类氧转移反应中的应用却非常有限。高催化剂负载量和不希望的副反应是四氧化钌催化碳-碳双键氧化反应中的严重缺点。最近，我们通过向反应混合物中加入布朗斯特酸，改进了四氧化钌催化的二羟基化反应。该方法被证明具有普遍适用性，然而，也观察到了某些局限性。为了解决这些有问题的官能团，我们开发了一种新的路易斯酸加速氧化方法。仅使用10 mol%的氯化铈就能使催化剂浓度进一步降低至0.25 mol%，同时拓宽了反应范围。在这个优化的方法中，甲硅烷基醚和含氮官能团现在是可以耐受的。此外，在路易斯酸存在下，竞争性的断裂反应受到抑制，从而允许更长的反应时间，并成功氧化了使用已知二羟基化方法无法氧化的缺电子四取代双键。
