Tandem Addition β-Lithiation−Alkylation Sequence on α,β-Unsaturated Aldehydes
作者:Norma Sbarbati Nudelman、Graciela V. García
DOI:10.1021/jo005698d
日期:2001.2.1
isotopic exchange reactions and trapping of two intermediates, provide clues on the several mechanistic steps of this new reaction. Extended studies revealed that beta-alkyl-substituted alpha,beta-unsaturated aldehydes and aliphatic lithium reagents did not afford good yields of the tandem reaction products, while aromatic lithium reagents gave good results. The aggregation features of the aryllithium
this study, wherein the cobalt‐ bidentate phosphine catalyst precursor is commercially available and the active low‐valent Co species could be generated in‐situ. For the conjugation enones, the vinyl group is selectively reduced, whereas with nonconjugated alkenones, the selectivity is changed to the carbonyl group. Besides, ortho‐alkenyl‐benzaldehydes/imines are well tolerated, and the reduction solely
这项研究开发了一种环境友好的方案,在无碱条件下用链烷醇对C = C和C = O键进行化学选择性转移加氢,其中钴二齿膦膦催化剂前体是可商购的,而活性低价Co物种可以原位生成。对于共轭烯酮,乙烯基被选择性地还原,而对于非共轭烯酮,选择性被改变为羰基。此外,邻链烯基苯甲醛/亚胺具有很好的耐受性,并且该方案仅在C = O / C = N位发生还原。
Transition-Metal-Free Highly Chemoselective and Stereoselective Reduction with Se/DMF/H<sub>2</sub>O System
metal-free reductionsystem, in which H2Se (or HSe–) produced in situ from Se/DMF/H2O acts as the active reducing species, has been developed. By using water as an inexpensive, safe, and environmentally friendly surrogate as the hydrogen donor, this newreductionsystem incorporating Se/DMF/H2O displayed high selectivity and good activity in the reduction of α,β-unsaturated ketones and alkynes. Therefore
一种新型的无金属还原系统,其中H 2 SE(或HSe组- )原位产生从硒/ DMF / H 2 ö充当活性还原物质,已经研制成功。通过使用水作为廉价,安全和环保的替代物作为氢供体,这种结合了Se / DMF / H 2 O的新还原系统在还原α,β-不饱和酮和炔烃方面显示出高选择性和良好的活性。因此,该还原系统具有很大的潜力,可以作为有机转化中通用而实用的还原方法。
How phenyl makes a difference: mechanistic insights into the ruthenium(<scp>ii</scp>)-catalysed isomerisation of allylic alcohols
作者:Simone Manzini、Albert Poater、David J. Nelson、Luigi Cavallo、Steven P. Nolan
DOI:10.1039/c3sc52612g
日期:——
[RuCl(η5-3-phenylindenyl)(PPh3)2] (1) has been shown to be a highly active catalyst for the isomerisation of allylic alcohols to the corresponding ketones. A variety of substrates undergo the transformation, typically with 0.25–0.5 mol% of catalyst at room temperature, outperforming commonly-used complexes such as [RuCl(Cp)(PPh3)2] and [RuCl(η5-indenyl)(PPh3)2]. Mechanistic experiments and density functional theory have been employed to investigate the mechanism and understand the effect of catalyst structure on reactivity. These investigations suggest a oxo-π-allyl mechanism is in operation, avoiding intermediate ruthenium hydride complexes and leading to a characteristic 1,3-deuterium shift. Important mechanistic insights from DFT and experiments also allowed for the design of a protocol that expands the scope of the transformation to include primary allylic alcohols.
Catalytic Hydrosilylation of Ketones Using a Co/Zr Heterobimetallic Complex: Evidence for an Unusual Mechanism Involving Ketyl Radicals
作者:Wen Zhou、Seth L. Marquard、Mark W. Bezpalko、Bruce M. Foxman、Christine M. Thomas
DOI:10.1021/om301194g
日期:2013.3.25
tris(phosphinoamide)-linked heterobimetallic Co/Zr complex (THF)Zr(MesNPiPr2)3CoN2 (1) has been investigated as a catalyst for the hydrosilylation of ketones with PhSiH3. Catalytic activity superior to monometallic Co or Zr analogues has been observed, demonstrating the importance of cooperative reactivity between Co and Zr. Upon examining stoichiometric reactions, complex 1 was found to be unreactive toward PhSiH3
已经研究了三(膦酰胺)连接的异双金属Co / Zr络合物(THF)Zr(MesNP i Pr 2)3 CoN 2(1)作为酮与PhSiH 3进行硅氢加成反应的催化剂。已观察到优于单金属Co或Zr类似物的催化活性,表明Co和Zr之间协同反应的重要性。通过检查化学计量反应,发现复合物1对PhSiH 3无反应,这表明该机理不同于典型的Chalk–Harrod型氢化硅烷化途径。相反,1易与酮反应,在二苯甲酮的情况下,分离出自由基偶联产物[(Ph 2 CO)Zr(MesNP i Pr 2)3 CoN 2 ] 2(3),这表明与Zr结合的酮基自由基具有中间性分段。提出了一种基于自由基的氢化硅烷化机制,该机制涉及氢原子从PhSiH 3转移到Zr结合的酮基自由基上。