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首页> 外文期刊>Chemistry: A European journal >Catalytic Asymmetric Baeyer–Villiger Oxidation in Water by Using PtII Catalysts and Hydrogen Peroxide: Supramolecular Control of Enantioselectivity
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Catalytic Asymmetric Baeyer–Villiger Oxidation in Water by Using PtII Catalysts and Hydrogen Peroxide: Supramolecular Control of Enantioselectivity

机译：使用PtII催化剂和过氧化氢催化水中不对称拜耳-维利格氧化反应：对映选择性的超分子控制

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摘要

The enantioselective Baeyer–Villiger oxidation of cyclic ketones is a challenging reaction, especially when using environmentally friendly oxidants. The reaction was carried out in water by using soft Lewis acid PtII complexes that have chiral diphosphines as well as monophosphines. Addition of a surfactant is crucial, which leads to the formation of micelles that act as nanoreactors in which the substrate and catalyst encounter each other in an ordered medium that in several cases positively influences both the conversion and the selectivity of the reactions. This is due to the combination of the hydrophobic effect (which confines the components of the reaction in the micelles), together with supramolecular interactions between the partners within the ordered palisade provided by the alkyl chains of the surfactant. For the oxidation of meso-cyclobutanones, addition of surfactant allowed the reaction to proceed in high yields and the enantiometic excess (ee; 56%) was higher than in organic solvents. Subsequent extension to meso-cyclohexanones resulted in a general decrease in yields but an enhancement of enantioselectivity (ee up to 92%) moving from organic to water–surfactant media, regardless of the substrate or the catalyst employed. Different behaviour was observed with chiral cyclobutanones 7 and 10: with 7 the best catalyst was 1g, whereas with the larger substrate, 10, complexes 1a–b performed better in terms of enantioselectivity. Each combination of substrate, catalyst and surfactant is a new system and supramolecular reciprocal interactions together with the hydrophobic character of the counterparts play crucial roles. The asymmetric Baeyer–Villiger oxidation in water catalyzed by 1a–h in the presence of micelles is a viable reaction that often benefits from the hydrophobic effect, leading to substantial increases in enantioselectivity.
机译：环状酮的对映选择性Baeyer-Villiger氧化反应具有挑战性，特别是在使用环境友好的氧化剂时。通过使用具有手性二膦以及单膦的软路易斯酸PtII配合物，在水中进行反应。表面活性剂的添加是至关重要的，这导致形成充当纳米反应器的胶束，其中底物和催化剂在有序介质中彼此相遇，在某些情况下，它们既积极影响反应的转化率，也影响反应的选择性。这是由于疏水作用（限制了胶束中反应的成分）以及表面活性剂烷基链提供的有序栅栏内的配偶之间的超分子相互作用的结合。对于内消旋环丁酮的氧化，表面活性剂的加入使反应以高产率进行，并且对映体过量（ee; 56％）高于有机溶剂。随后扩展为内环己酮导致收率普遍下降，但对映选择性（ee高达92％）从有机介质转移至水表面活性剂介质，无论所用的底物或催化剂如何。手性环丁酮7和10观察到不同的行为：7时最好的催化剂是1g，而较大的底物10时，配合物1a–b在对映选择性方面表现更好。底物，催化剂和表面活性剂的每种组合都是一个新系统，超分子的相互作用以及对应物的疏水性起着至关重要的作用。在胶束存在下，以1a–h催化的水中不对称Baeyer–Villiger氧化是一个可行的反应，通常受益于疏水作用，导致对映选择性大大提高。

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