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。
Iron-Catalyzed Enantioselective Cross-Coupling Reactions of α-Chloroesters with Aryl Grignard Reagents
The first iron-catalyzed enantioselective cross-coupling reaction between an organometallic compound and an organic electrophile is reported. Synthetically versatile racemic α-chloro- and α-bromoalkanoates were coupled with aryl Grignard reagents in the presence of catalytic amounts of an iron salt and a chiral bisphosphine ligand, giving the products in high yields with acceptable and synthetically
centers via C–C coupling protocols remains challenging. The coupling of tertiary C(sp3) with secondary or tertiary C(sp3) counterparts has been hindered by pronounced steric clashes and many side reactions. Herein, we have successfully developed a type of bisphosphine ligand iron complex-catalyzed coupling reactions of tertiaryalkylhalides with secondary alkyl zinc reagents and efficiently realized the
C(sp2)-C(sp3) cross-coupling reactions has been studied via the synthesis of novel radical-clock α-halo-esters and quantum mechanical calculations. These results provide insights into the role of the substrate (halogen and substituents) in competing in-cage and out-of-cage arylation pathways and provide a basis for the future rational design of novel tandem cyclization-arylation reactions using bisphosphine-iron