115976-33-5Relevant articles and documents
Mechanistic investigations of the palladium-catalyzed aerobic oxidative kinetic resolution of secondary alcohols using (-)-Sparteine
Mueller, Jaime A.,Sigman, Matthew S.
, p. 7005 - 7013 (2003)
The mechanistic details of the Pd(II)/(-)-sparteine-catalyzed aerobic oxidative kinetic resolution of secondary alcohols were elucidated, and the origin of asymmetric induction was determined. Saturation kinetics were observed for rate dependence on [(-)-sparteine]. First-order rate dependencies were observed for both the Pd((-)-sparteine)Cl2 concentration and the alcohol concentration at high and low [(-)-sparteine]. The oxidation rate was inhibited by addition of (-)-sparteine HCl. At low [(-)-sparteine], Pd-alkoxide formation is proposed to be rate limiting, while at high [(-)-sparteine], β-hydride elimination is proposed to be rate determining. These conclusions are consistent with the measured kinetic isotope effect of kH/kD = 1.31 ± 0.04 and a Hammett ρ value of -1.41 ± 0.15 at high [(-)-sparteine]. Calculated activation parameters agree with the change in the rate-limiting step by increasing [(-)-sparteine] with ΔH? = 11.55 ± 0.65 kcal/ mol, ΔS? = -24.5 ± 2.0 eu at low [(-)-sparteine], and ΔH? = 20.25 ± 0.89 kcal/mol, ΔS? = -5.4 ± 2.7 eu at high [(-)-sparteine]. At high [(-)-sparteine], the selectivity is influenced by both a thermodynamic difference in the stability of the diastereomeric Pd-alkoxides formed and a kinetic β-hydride elimination to maximize asymmetric induction. At low [(-)-sparteine], the selectivity is influenced by kinetic deprotonation, resulting in lower krel values. A key, nonintuitive discovery is that (-)-sparteine plays a dual role in this oxidative kinetic resolution of secondary alcohols as a chiral ligand on palladium and as an exogenous chiral base.
A comparative study of the McMurry reaction utilizing x, TiCl3(DME)1.5-Zn(Cu) and TiCl2 * LiCl as coupling reagents
Bogdanovic, Borislav,Bolte, Andreas
, p. 109 - 122 (1995)
An investigation of the reaction course and stoichiometry of the McMurry reaction of acetophenone utilizing x (THF=tetrahydrofuran), TiCl3(DME)1.5-Zn(Cu) (DME=1,2-dimethoxyethane) and TiCl2*LiCl as coupling reagents has been undertaken.The detection of 1-phenylethanol (3a) or dideutero-1-phenylethanol (3b) (Schemes 1 and 3) as hydrolysis or deuterolysis products in the early stage of reactions gave the first direct experimental evidence for the occurence of the "side-on" bonded ketones 3 and 3" as possible precursors of the pinacolates 4 and 7.This result supports the nucleophilic rather than the radical mechanism for the C-C coupling step of aromatic ketones.Contrary to the current opinion, upon refluxing TiCl3(DME)1.5-Zn(Cu) mixtures in DME, no reduction of Ti3+ to low valence Ti species could be detected.The reduction of Ti3+ by Zn (Scheme 2) only starts in the presence of the carbonyl substrate which is coordinated to the Ti (the "instant method"); both the ketone-> pinacolate and the pinacolate-> alkene steps (Scheme 2) apparently involve a transient reduction of Ti3+ by Zn.This view is supported by experiments in which TiCl2*LiCl is used as a reagent and in which it behaves as a one-electron reductant (Scheme 3).On the basis of these results, the overall stoichiometry of the McMurry reaction utilizing TiCl3(DME)1.5-Zn(Cu) as a reagent can be represented by Eq. (4).High yields (95-97percent) of the alkene 2 in acceptable reaction times can already be achieved with an acetophenone: TiCl3(DME)1.5:Zn(Cu) molar ratio of 1:2:2.A conclusion which can be drawn from the results is that the McMurry reaction when performed with two of the most commonly applied reagents, namely TiCl3-LiAlH4-THF (in fact HTiCl(THF)0.5!) and TiCl3(DME)1.5-Zn(Cu)-DME, is mainly associated with changes in the (formal) oxidation state of titanium between Ti2+ and Ti3+.Keywords: McMurry reaction; TiCl3(1,2-dimethoxyethane); Low valent titanium-ketone complexes
“Inverse” Frustrated Lewis Pairs: An Inverse FLP Approach to the Catalytic Metal Free Hydrogenation of Ketones
Mummadi, Suresh,Brar, Amandeep,Wang, Guoqiang,Kenefake, Dustin,Diaz, Rony,Unruh, Daniel K.,Li, Shuhua,Krempner, Clemens
supporting information, p. 16526 - 16531 (2018/10/20)
For the first time have boron-containing weak Lewis acids been demonstrated to be active components of Frustrated Lewis Pair (FLP) catalysts in the hydrogenation of ketones to alcohols. Combining the organosuperbase (pyrr)3P=NtBu with the Lewis acid 9-(4-CF3-C6H4)-BBN generated an “inverse” FLP catalyst capable of hydrogenating a range of aliphatic and aromatic ketones including N-, O- and S-functionalized substrates and bio-mass derived ethyl levulinate. Initial computational and experimental studies indicate the mechanism of catalytic hydrogenation with “inverse” FLPs to be different from conventional FLP catalysts that contain strong Lewis acids such as B(C6F5)3.
Direct, metal-free synthesis of benzyl alcohols and deuterated benzyl alcohols from p-toluenesulfonylhydrazones using water as solvent
Garcia-Munoz, Angel,Ortega-Arizmendi, Aldo I.,Garcia-Carrillo, Mario A.,Diaz, Eduardo,Gonzalez-Rivas, Nelly,Cuevas-Yanez, Erick
supporting information; experimental part, p. 2237 - 2242 (2012/09/22)
A novel library of diverse alcohols was synthesized by metal-free couplings of diazoalkanes derived from p-toluenesulfonylhydrazones to water under reflux and microwave conditions, in high yields. In addition, this protocol was successfully applied in the synthesis of deuterium-labeled alcohols using deuterium oxide. Georg Thieme Verlag Stuttgart New York.
