osmium-catalyzed dihydroxylation has uncovered that electron-deficient olefins are converted into the corresponding diols much more efficiently when the pH of the reaction medium is maintained on the acidic side. Further studies have identified citric acid as the additive of choice, for it allows preparation of very pure diols in yields generally exceeding 90%. As described here, a much wider range of olefin classes
substrate concentrations (up to 75 g/L) to be reached. Even extremely sterically demanding epoxides such as cis‐ and trans‐stilbene oxides were transformed on a reasonable time scale. All reactions were successfully conducted on a 1 g preparative scale, generating diol‐ and epoxide‐based chiral synthons with very high enantiomeric excesses and isolated yields close to the theoretical maximum. Thus we
已用十种不同的外消旋和内消旋体测试了在大肠杆菌RE3中过表达的环氧水解酶Kau2α,β-二取代的芳族环氧化物。一些经过测试的底物是双功能的,其中大多数是合成化学应用中非常有用的构建基块。作为一种普遍趋势,Kau2被证明是一种对映体选择性极强的生物催化剂,除了几乎对映体纯净的形式外,还获得了生物转化的二醇产物和剩余的环氧化物(有两个例外)。此外,反应时间通常很短(大约1小时,使用二氧化二苯乙烯时除外),并且有机共溶剂的使用被很好地耐受,从而可以达到很高的底物浓度(最高75 g / L)。 。甚至对空间要求极高的环氧化物,例如顺式和反式sti氧化物在合理的时间范围内转化。所有反应均以1 g制备规模成功进行,生成了对映体过量非常高且分离出的收率接近理论最大值的基于二醇和环氧化物的手性合成子。因此,我们在这里证明了表达Kau2环氧水解酶作为高度对映选择性的生物催化剂的冻干大肠杆菌细胞的有用性和多功
Synthese und Stereochemie β-substituierter Glycerinsäurenitrile
作者:Wolfgang Althoff、Rudolf Karsdorf、Peter Tinapp
DOI:10.1002/ardp.19813140609
日期:——
Ein einfacher Weg zur Synthesevon β‐substituierten Glycerinsäurenitrilen 3 wird beschrieben. Die neuen Verbindungen werden als O‐geschützte Derivate 4 und 5 charakterisiert und stereochemisch eingeordnet. Reduktion von 5 führt zu einem neuenTyp pharmakologisch interessanter basischer 1.3‐Dioxolane 6. Partielle Reduktion der O‐geschützten Cyanhydrine 4 oder 5 nach einer früher beschriebenen Methode
Biotransformations of 2,3-epoxy-3-arylpropanenitriles by Debaryomyces hansenii and Mortierella isabellina cells
作者:Malgorzata Zagozda、Jan Plenkiewicz
DOI:10.1016/j.tetasy.2008.06.004
日期:2008.6
Biotransformations of five substituted cis- and trans-oxiranecarbonitriles with Mortierella isabellina DSM 1414, a microbial whole-cell catalyst producing epoxide hydrolases, were investigated. The reactions were stopped when the conversion of the substrates reached 50%. They yielded the appropriate optically active dihydroxycarbonitriles and oxiranecarbonitriles in low enantiomeric purity. Kinetic resolution of rac-syn-2,3-diliydroxy-3-arylpropanenitriles by lipase catalyzed acetylation yielded almost enantiomerically pure (-)-dihydroxynitriles and mixtures of regioisomers of monoacetylated diols. Another microorganism, Debaryomyces hansenii DSM 3428, was used as a source of nitrile hydratases in the kinetic resolution of oxiranecarbonitriles. Only two trans-configured compounds were transformed into the corresponding oxiranecarboxamides. (C) 2008 Elsevier Ltd. All rights reserved.
The acid accelerated ruthenium-catalysed dihydroxylation. Scope and limitations
作者:Bernd Plietker、Meike Niggemann、Anja Pollrich
DOI:10.1039/b316546a
日期:——
Recently, we discovered a significant rate acceleration in RuO4-catalysed dihydroxylations of olefins by addition of Brönsted-acids resulting in a reduction of the catalyst loading to only 0.5 mol%. The present paper gives a full account on the optimisation protocol that led to the discovery of the beneficial influence of protic acids. A strong focus is set on the detailed description of the influence of different reaction parameters on both reactivity and selectivity. In the second part an intense investigation of scope and limitations will be presented. The results provided in this manuscript might lead to a deeper understanding of competing processes that influence the selectivity in RuO4-catalysed dihydroxylations.