Mechanism of the Ni(0)-Catalyzed Vinylcyclopropane−Cyclopentene Rearrangement
摘要:
A combination of physical organic experiments and quantum chemical calculations were used to construct a detailed mechanistic model for the Ni(0)-N-heterocyclic carbene-catalyzed vinylcyclo-propane-cyclopentene rearrangement that involves a mutistep oxidative addition/haptotropic shift/reductive elimination pathway. No evidence for the intermediacy of radicals or zwitterions was found. The roles of substituents on the vinylcyclopropane substrate and variations in the ligands on Ni were evaluated. It is postulated that bulky carbene ligands facilitate formation of the active catalyst species.
Stereoselective Alkyne Hydrogenation by using a Simple Iron Catalyst
作者:Bernhard J. Gregori、Felix Schwarzhuber、Simon Pöllath、Josef Zweck、Lorena Fritsch、Roland Schoch、Matthias Bauer、Axel Jacobi von Wangelin
DOI:10.1002/cssc.201900926
日期:2019.8.22
stereoselective hydrogenation of alkynes constitutes one of the key approaches for the construction of stereodefined alkenes. The majority of conventional methods utilize noble and toxic metal catalysts. This study concerns a simple catalyst comprised of the commercial chemicals iron(II) acetylacetonate and diisobutylaluminum hydride, which enables the Z-selective semihydrogenation of alkynes under near ambient
炔烃的立体选择性加氢构成构造立体烯烃的关键方法之一。大多数常规方法利用贵金属和有毒金属催化剂。这项研究涉及一种由工业化学品乙酰丙酮铁(II)和氢化二异丁基铝组成的简单催化剂,该催化剂能够在接近环境条件(1-3 bar H2、30°C,5 mol%[Fe] )。既不需要复杂的催化剂制备也不需要添加配体。机理研究(动力学中毒,X射线吸收光谱法,TEM)强烈表明了小铁簇和颗粒催化剂的运行。
Nickel-Catalyzed System for the Cross-Coupling of Alkenyl Methyl Ethers with Grignard Reagents under Mild Conditions
A nickel-catalyzed cross-coupling of alkenyl methyl ethers with Grignard reagents, undermildconditions, is described. These conditions allowed access to various stilbenes and heterocyclic stilbenic derivatives as well as to a potential anticancer agent DMU-212.
Stereoselective Chromium‐Catalyzed Semi‐Hydrogenation of Alkynes
作者:Bernhard J. Gregori、Michal Nowakowski、Anke Schoch、Simon Pöllath、Josef Zweck、Matthias Bauer、Axel Jacobi von Wangelin
DOI:10.1002/cctc.202000994
日期:2020.11.5
very little applications as hydrogenation catalysts. Here, we report a Cr‐catalyzed semi‐hydrogenation of internal alkynes to the corresponding Z‐alkenes with good stereocontrol (up to 99/1 for dialkyl alkynes). The catalyst comprises the commercial reagents chromium(III) acetylacetonate, Cr(acac)3, and diisobutylaluminium hydride, DIBAL−H, in THF. The semi‐hydrogenation operates at mild conditions
Iron-Catalyzed Cross-Coupling of 1-Alkynylcyclopropyl Tosylates and Related Substrates
作者:Daniel J. Tindall、Helga Krause、Alois Fürstner
DOI:10.1002/adsc.201600357
日期:2016.7.28
1‐Alkynylcyclopropyl tosylates react with alkylmagnesium halides in the presence of catalytic ferric acetylacetonate [Fe(acac)3] under net propargylic substitution; allene formation, which is the prevalent reactivity mode of propargylic substrates otherwise, was noticed as a side reaction only when branched alkyl‐ or aryl‐Grignard reagents were used. These transformations represent the first successful iron‐catalyzed
new synthetic methodology for preparing cyclopropanes is presented. The reaction involves a cooperative zirconium- and Lewis acid-mediated deoxygenative coupling of carbonyl compounds with a Grignard reagent. In this way, various cyclopropanes are obtained in moderate to excellent yields, directly from saturated, unsaturated, and aromatic aldehydes and ketones. This reaction tolerates the presence of