Treasures from the Free Radical Renaissance Period – Miscellaneous hexenyl radical kinetic data
作者:Athelstan L. J. Beckwith、Carl H. Schiesser
DOI:10.1039/c0ob00708k
日期:——
Rate constant data and Arrhenius parameters have been determined for a series of substituted hexenyl radicals of differing electronic and steric demand. Electron-withdrawing groups (CF3, CO2Et) directly attached to the radical centre slighly accelerate 5-exo ring-closure (kcis + ktrans ∼ 2.1 × 105 s−1 at 25°) relative to donating groups (OMe; 1.6 × 105 s−1 at 25°). Sterically demanding groups (tert-Bu)
已针对一系列具有不同电子和空间需求的取代己烯基确定了速率常数数据和Arrhenius参数。相对于捐赠基团(OMe ),直接连接至自由基中心的吸电子基团(CF 3,CO 2 Et)缓慢促进5- exo闭环(25°时k cis + k trans〜2.1 ×10 5 s -1) ;在25°时为1.6×10 5 s -1)。如预期的那样,对空间要求较高的组(叔-Bu )减慢环化过程(1×10 5 s -1)。这些观察结果与5 - exo闭环的活化能的细微变化是一致的。有趣的是,溶剂的性质似乎对该化学有重大影响,随着溶剂极性的增加,顺式/反式立体选择性有时会提高。除了包含CF 3(吸电子)基团的系统显示出环化/捕获速率常数(k c / k H)增加外,k c / k H普遍下降。记录随着溶剂极性增加的比率;据推测,这些变化主要是由于所用各种溶剂中k H的变化引起的。
Fast-Initiating, Ruthenium-based Catalysts for Improved Activity in Highly <i>E</i>-Selective Cross Metathesis
作者:Tonia S. Ahmed、Robert H. Grubbs
DOI:10.1021/jacs.6b11330
日期:2017.2.1
Ruthenium-based olefinmetathesis catalysts bearing dithiolate ligands have been recently employed to generate olefins with high E-selectivity (>99% E) but have been limited by low to moderate yields. In this report, 1H NMR studies reveal that a major contributingfactor to this low activity is the extremely low initiation rates of these catalysts with trans olefins. Introducing a 2-isopropoxy-3-phenylbenzylidene
High <i>Trans</i> Kinetic Selectivity in Ruthenium-Based Olefin Cross-Metathesis through Stereoretention
作者:Adam M. Johns、Tonia S. Ahmed、Bradford W. Jackson、Robert H. Grubbs、Richard L. Pederson
DOI:10.1021/acs.orglett.6b00031
日期:2016.2.19
controlled, highly trans-selective (>98%) olefin cross-metathesis reaction is demonstrated using Ru-based catalysts. Reactions with either trans or cis olefins afford products with highly trans or cis stereochemistry, respectively. This E-selective olefin cross-metathesis is shown to occur between two trans olefins and between a trans olefin and a terminal olefin. Additionally, new stereoretentive catalysts
[EN] OLEFIN METATHESIS CATALYSTS<br/>[FR] CATALYSEURS DE MÉTATHÈSE D'OLÉFINES
申请人:MATERIA INC
公开号:WO2017100585A1
公开(公告)日:2017-06-15
This invention relates generally to metathesis catalysts and the use of such catalysts in the metathesis of olefins and olefin compounds, more particularly, in the use of such catalysts in Z and E selective olefin metathesis reactions. The invention has utility in the fields of organometallics and organic synthesis.
Regioselective Carbon-Carbon Bond Formation in Titanium Mediated Reaction of Ethylmagnesium Bromide with Allylic Alcohols and Allylic Ethers
作者:Oleg G. Kulinkovich、Oleg L. Epstein、Vladimir E. Isakov、Ekaterina A. Khmel'nitskaya
DOI:10.1055/s-2001-9707
日期:——
In the presence of Ti(Oi-Pr)4 reaction of EtMgBr with allylic alcohols and allylicethers affords the products of formal SN2′ substitution of hydroxy or alkoxy groups with ethyl groups in moderate to good yields and excellent regioselectivity. The mechanism of the reaction includes the formation of titanacyclopropanes as the key organometallic intermediates. Promoting action of EtMgBr on the process