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CATALYSIS WITH TRICARBONYL-tetrahapto-CYCLOPENTADIENONERUTHENIUM(0) COMPLEXES. A WATER-GAS TYPE REACTION
With water tricarbonyl-tetrahapto-tetraphenylcyclopentadienoneruthenium(0) (1) undergoes a water-gas type reaction whereby a coordinated CO is oxidized to CO2, and gives the dimeric complex, which was isolated in high yield.A catalytic reduction of ketones with CO and water under mild conditions has been developed, and a catalytic cycle proposed.A turnover frequency of 1.2 min-1, which is increased by a factor of ca. 6 by the presence of sodium carbonate, has been observed in the reactions with cyclohexanone.
Shvo, Youval,Czarkie, Dorotha
p. C25 - C28
(1986)
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Highly efficient NHC-iridium-catalyzed β-methylation of alcohols with methanol at low catalyst loadings
The methylation of alcohols is of great importance since a broad number of bioactive and pharmaceutical alcohols contain methyl groups. Here, a highly efficient β-methylation of primary and secondary alcohols with methanol has been achieved by using bis-N-heterocyclic carbene iridium (bis-NHC-Ir) complexes. Broad substrate scope and up to quantitative yields were achieved at low catalyst loadings with only hydrogen and water as by-products. The protocol was readily extended to the β-alkylation of alcohols with several primary alcohols. Control experiments, along with DFT calculations and crystallographic studies, revealed that the ligand effect is critical to their excellent catalytic performance, shedding light on more challenging Guerbet reactions with simple alcohols. [Figure not available: see fulltext.].
Lu, Zeye,Zheng, Qingshu,Zeng, Guangkuo,Kuang, Yunyan,Clark, James H.,Tu, Tao
p. 1361 - 1366
(2021/06/30)

A Practical and Stereoselective In Situ NHC-Cobalt Catalytic System for Hydrogenation of Ketones and Aldehydes
Homogeneous catalytic hydrogenation of carbonyl groups is a synthetically useful and widely applied organic transformation. Sustainable chemistry goals require replacing conventional noble transition metal catalysts for hydrogenation by earth-abundant base metals. Herein, we report how a practical in situ catalytic system generated by easily available pincer NHC precursors, CoCl2, and a base enabled efficient and high-yielding hydrogenation of a broad range of ketones and aldehydes (over 50 examples and a maximum turnover number [TON] of 2,610). This is the first example of NHC-Co-catalyzed hydrogenation of C=O bonds using flexible pincer NHC ligands consisting of a N-H substructure. Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized by fine-tuning of the steric bulk of pincer NHC ligands. Additionally, a bis(NHCs)-Co complex was successfully isolated and fully characterized, and it exhibits excellent catalytic activity that equals that of the in-situ-formed catalytic system. Catalytic hydrogenation is a powerful tool for the reduction of organic compounds in both fine and bulk chemical industries. To improve sustainability, more ecofriendly, inexpensive, and earth-abundant base metals should be employed to replace the precious metals that currently dominate the development of hydrogenation catalysts. However, the majority of the base-metal catalysts that have been reported involve expensive, complex, and often air- and moisture-sensitive phosphine ligands, impeding their widespread application. From a mixture of the stable CoCl2, imidazole salts, and a base, our newly developed catalytic system that formed easily in situ enables efficient and stereoselective hydrogenation of C=O bonds. We anticipate that this easily accessible catalytic system will create opportunities for the design of practical base-metal hydrogenation catalysts. A practical in situ catalytic system generated by a mixture of easily available pincer NHC precursors, CoCl2, and a base enabled highly efficient hydrogenation of a broad range of ketones and aldehydes (over 50 examples and up to a turnover number [TON] of 2,610). Diastereodivergent hydrogenation of substituted cyclohexanone derivatives was also realized in high selectivities. Moreover, the preparation of a well-defined bis(NHCs)-Co complex via this pincer NHC ligand consisting of a N-H substructure was successful, and it exhibits equally excellent catalytic activity for the hydrogenation of C=O bonds.
Zhong, Rui,Wei, Zeyuan,Zhang, Wei,Liu, Shun,Liu, Qiang
supporting information
p. 1552 - 1566
(2019/06/14)

Transfer Hydrogenation of Carbonyl Groups, Imines and N-Heterocycles Catalyzed by Simple, Bipyridine-Based MnI Complexes
Utilization of hydroxy-substituted bipyridine ligands in transition metal catalysis mimicking [Fe]-hydrogenase has been shown to be a promising approach in developing new catalysts for hydrogenation. For example, MnI complexes with 6,6′-dihydroxy-2,2′-bipyridine ligand have been previously shown to be active catalysts for CO2 hydrogenation. In this work, simple bipyridine-based Mn catalysts were developed that act as active catalysts for transfer hydrogenation of ketones, aldehydes and imines. For the first time, Mn-catalyzed transfer hydrogenation of N-heterocycles was reported. The highest catalytic activity among complexes with variously substituted ligands was observed for the complex bearing two OH groups in bipyridine. Deuterium labeling experiments suggest a monohydride pathway.
Dubey, Abhishek,Rahaman, S. M. Wahidur,Fayzullin, Robert R.,Khusnutdinova, Julia R.
p. 3844 - 3852
(2019/04/08)

Chemoselective Oxidation of Equatorial Alcohols with N-Ligated λ3-Iodanes
The site-selective and chemoselective functionalization of alcohols in complex polyols remains a formidable synthetic challenge. Whereas significant advancements have been made in selective derivatization at the oxygen center, chemoselective oxidation to the corresponding carbonyls is less developed. In cyclic systems, whereas the selective oxidation of axial alcohols is well known, a complementary equatorial selective process has not yet been reported. Herein we report the utility of nitrogen-ligated (bis)cationic λ3-iodanes (N-HVIs) for alcohol oxidation and their unprecedented levels of selectivity for the oxidation of equatorial over axial alcohols. The conditions are mild, and the simple pyridine-ligated reagent (Py-HVI) is readily synthesized from commercial PhI(OAc)2 and can be either isolated or generated in situ. Conformational selectivity is demonstrated in both flexible 1,2-substituted cyclohexanols and rigid polyol scaffolds, providing chemists with a novel tool for chemoselective oxidation.
Mikhael, Myriam,Adler, Sophia A.,Wengryniuk, Sarah E.
supporting information
p. 5889 - 5893
(2019/08/26)

PROCESS FOR MAKING FORMIC ACID UTILIZING LOWER-BOILING FORMATE ESTERS
Disclosed is a process for recovering formic acid from a formate ester of a C3 to C4 alcohol. Disclosed is also a process for producing formic acid by carbonylating a C3 to C4 alcohol, hydrolyzing the formate ester of the alcohol, and recovering a formic acid product. The alcohol may be dried and returned to the reactor. The process enables a more energy efficient production of formic acid than the carbonylation of methanol to produce methyl formate.
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Paragraph 00177; 00178

(2019/02/15)

Carbonyl and ester C-O bond hydrosilylation using κ4-diimine nickel catalysts
The synthesis of alkylphosphine-substituted α-diimine (DI) ligands and their subsequent addition to Ni(COD)2 allowed for the preparation of (iPr2PPrDI)Ni and (tBu2PPrDI)Ni. The solid state structures of both compounds were found to feature a distorted tetrahedral geometry that is largely consistent with the reported structure of the diphenylphosphine-substituted variant, (Ph2PPr DI)Ni. To explore and optimize the synthetic utility of this catalyst class, all three compounds were screened for benzaldehyde hydrosilylation activity at 1.0 mol% loading over 3 h at 25 °C. Notably, (Ph2PPr DI)Ni was found to be the most efficient catalyst while phenyl silane was the most effective reductant. A broad scope of aldehydes and ketones were then hydrosilylated, and the silyl ether products were hydrolyzed to afford alcohols in good yield. When attempts were made to explore ester reduction, inefficient dihydrosilylation was noted for ethyl acetate and no reaction was observed for several additional substrates. However, when an equimolar solution of allyl acetate and phenyl silane was added to 1.0 mol% (Ph2PPr DI)Ni, complete ester C-O bond hydrosilylation was observed within 30 min at 25 °C to generate propylene and PhSi(OAc)3. The scope of this reaction was expanded to include six additional allyl esters, and under neat conditions, turnover frequencies of up to 990 h-1 were achieved. This activity is believed to be the highest reported for transition metal-catalyzed ester C-O bond hydrosilylation. Proposed mechanisms for (Ph2PPr DI)Ni-mediated carbonyl and allyl ester C-O bond hydrosilylation are also discussed.
Rock, Christopher L.,Groy, Thomas L.,Trovitch, Ryan J.
supporting information
p. 8807 - 8816
(2018/07/13)

“Inverse” Frustrated Lewis Pairs: An Inverse FLP Approach to the Catalytic Metal Free Hydrogenation of Ketones
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.
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)

A Versatile Iridium(III) Metallacycle Catalyst for the Effective Hydrosilylation of Carbonyl and Carboxylic Acid Derivatives
A versatile iridium(III) metallacycle catalysed rapidly and selectively the reduction of a large array of challenging esters and carboxylic acids as well as various ketones and aldehydes. The reactions proceeded in high yields at room temperature by hydrosilylation followed by desilylation. Although the reactions of various aldehydes and ketones resulted exclusively in alcohols, the hydrosilylation of esters led to alcohols or ethers, depending on the type of substrate. Regarding the carboxylic acids, again the nature of the reagent controlled the outcome of the hydrosilylation reaction, either alcohols or aldehydes being formed.
Corre, Yann,Rysak, Vincent,Trivelli, Xavier,Agbossou-Niedercorn, Francine,Michon, Christophe
p. 4820 - 4826
(2017/09/07)

CATALYST AND METHOD FOR HYDROGENATION OF 1,3-CYCLOBUTANEDIKETONE COMPOUND
Catalyst for hydrogenation of 1,3-cyclobutanediketone compound is provided, which includes a support and VIIIB group transition metal loaded thereon. The support includes a first oxide powder with a surface wrapped by a second oxide. The first oxide includes silicon oxide, aluminum oxide, zirconium oxide, titanium oxide, zinc oxide, or a combination thereof. The second oxide has a composition of MxAl(1-x)O(3-x)/2, M is alkaline earth metal, and x is from 0.3 to 0.7.
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Paragraph 0032

(2017/12/27)

Synthesis, characterization and reactivity of iron- and cobalt-pincer complexes
The tBuPONOP (2,6-bis(di-tert-butyl-phosphinito)pyridine) complexes of iron and cobalt, (tBuPONOP)FeCl2 (1) and (tBuPONOP)CoCl2 (2)) have been prepared. Both complexes are paramagnetic and the solid-state structures of 1 and 2 were determined by single crystal X-ray diffraction studies. Analogous Fe and Co complexes of the tBuPNP (2,6-bis(di-tert-butyl-phosphinomethyl)pyridine) ligand (3 and 4, respectively) were prepared to allow comparison between the closely related pincer ligands in the hydrosilylation of carbonyl moieties. All four complexes were found to be catalytically active when treated with NaBEt3H, which was assumed to generate a metal-hydride species in-situ.
Smith, Ashleigh D.,Saini, Anu,Singer, Laci M.,Phadke, Neha,Findlater, Michael
p. 286 - 291
(2016/07/06)

Iron-Catalyzed Hydrosilylation of Aldehydes and Ketones under Solvent-Free Conditions
Exposure of aldehyde or ketone to 1 mol % BIAN-Fe(C7H8) complex in the presence of diphenyl silane affords the corresponding protected alcohol in excellent yields, under mild reaction conditions. Aldehydes and ketones are reduced cleanly in the presence of a broad range of functional groups under solvent-free conditions.
Wekesa, Francis S.,Arias-Ugarte, Renzo,Kong, Lydia,Sumner, Zachary,McGovern, Gregory P.,Findlater, Michael
p. 5051 - 5056
(2015/11/09)

Substrate flexibility and reaction specificity of tropinone reductase-like short-chain dehydrogenases
Annotations of protein or gene sequences from large scale sequencing projects are based on protein size, characteristic binding motifs, and conserved catalytic amino acids, but biochemical functions are often uncertain. In the large family of short-chain dehydrogenases/reductases (SDRs), functional predictions often fail. Putative tropinone reductases, named tropinone reductase-like (TRL), are SDRs annotated in many genomes of organisms that do not contain tropane alkaloids. SDRs in vitro often accept several substrates complicating functional assignments. Cochlearia officinalis, a Brassicaceae, contains tropane alkaloids, in contrast to the closely related Arabidopsis thaliana. TRLs from Arabidopsis and the tropinone reductase isolated from Cochlearia (CoTR) were investigated for their catalytic capacity. In contrast to CoTR, none of the Arabidopsis TRLs reduced tropinone in vitro. NAD(H) and NADP(H) preferences were relaxed in two TRLs, and protein homology models revealed flexibility of amino acid residues in the active site allowing binding of both cofactors. TRLs reduced various carbonyl compounds, among them terpene ketones. The reduction was stereospecific for most of TRLs investigated, and the corresponding terpene alcohol oxidation was stereoselective. Carbonyl compounds that were identified to serve as substrates were applied for modeling pharmacophores of each TRL. A database of commercially available compounds was screened using the pharmacophores. Compounds identified as potential substrates were confirmed by turnover in vitro. Thus pharmacophores may contribute to better predictability of biochemical functions of SDR enzymes.
Reinhardt, Nicole,Fischer, Juliane,Coppi, Ralph,Blum, Elke,Brandt, Wolfgang,Draeger, Birgit
p. 37 - 49
(2014/03/21)

Zincocene and dizincocene N-heterocyclic carbene complexes and catalytic hydrogenation of imines and ketones
The N-heterocyclic carbene (NHC) adducts Zn(CpR) 2(NHC)] (CpR=C5HMe4, C 5H4SiMe3; NHC=ItBu, IDipp (Dipp=2,6- diisopropylphenyl), IMes (Mes=mesityl), SIMes) were prepared and shown to be active catalysts for the hydrogenation of imines, whereas decamethylzincocene [ZnCp*2] is highly active for the hydrogenation of ketones in the presence of noncoordinating NHCs. The abnormal carbene complex [Zn(OCHPh2)2(aItBu)]2 was formed from spontaneous rearrangement of the ItBu ligand during incomplete hydrogenation of benzophenone. Two isolated ZnI adducts [Zn2Cp* 2(NHC)] (NHC=ItBu, SIMes) are presented and characterized as weak adducts on the basis of 13C NMR spectroscopic and X-ray diffraction experiments. A mechanistic proposal for the reduction of [ZnCp* 2] with H2 to give [Zn2Cp*2] is discussed.
Jochmann, Phillip,Stephan, Douglas W.
supporting information
p. 8370 - 8378
(2014/07/08)

A well-defined monomeric aluminum complex as an efficient and general catalyst in the Meerwein-Ponndorf-Verley reduction
The metal-catalyzed Meerwein-Ponndorf-Verley (MPV) reduction allows for the mild and sustainable reduction of aldehydes and ketones but has not found widespread application in organic synthesis due to the high catalyst loading often required to obtain satisfactory yields of the reduced product. We report here on the synthesis and structure of a sterically extremely overloaded siloxide-supported aluminum isopropoxide capable of catalytically reducing a wide range of aldehydes and ketones (52 examples) in excellent yields under mild conditions and with low catalyst loadings. The unseen activity of the developed catalyst system in MPV reductions is due to its unique monomeric nature and the neutral donor isopropanol weakly coordinating to the aluminum center. The present work implies that monomeric aluminum alkoxide catalysts may be attractive alternatives to transition-metalbased systems for the selective reduction of aldehydes and ketones to primary and secondary alcohols.
McNerney, Brian,Whittlesey, Bruce,Cordes, David B.,Krempner, Clemens
supporting information
p. 14959 - 14964
(2015/01/08)

6,6′-Dihydroxy terpyridine: A proton-responsive bifunctional ligand and its application in catalytic transfer hydrogenation of ketones
The ligand 6,6′-dihydroxy terpyridine (dhtp) is presented as a bifunctional ligand capable of directing proton transfer events with metal-coordinated substrates. Solid-state analysis of a Ru(ii)-dhtp complex reveals directed hydrogen-bonding interactions of the hydroxyl groups of dhtp with a Ru-bound chloride ligand. The utility of dhtp was demonstrated by chemoselective transfer hydrogenation of ketones.
Moore, Cameron M.,Szymczak, Nathaniel K.
supporting information
p. 400 - 402
(2013/02/22)

PROCESS FOR THE ISOMERIZATION OF 2,2,4,4-TETRAALKYLCYCLOBUTANE-1,3-DIOLS
Disclosed is a process for the isomerization of 2,2,4,4-tetraalkylcyclobutane-1,3-diols, such as 2,2,4,4-tetramethylcyclobutane-1,3-diol, by contacting the diol with a supported ruthenium catalyst in the presence of hydrogen at elevated pressures and temperatures. The process is carried under conditions in which there is no net production of 2,2,4,4-tetraalkylcyclobutane-1,3-diol. The process may be carried out in the presence or absence of a solvent and in the liquid or vapor phase.
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Page/Page column 7

(2012/06/18)

Hydrogenation of hindered ketones catalyzed by a silica-supported compact phosphine-Rh system
(Chemical Equation Presented) A heterogeneous mono(phosphine)-Rh catalyst system silica-SMAP-Rh(OMe)(cod), where silica-SMAP stands for a caged, compact trialkylphosphine (SMAP) supported on silica gel, showed broad applicability toward the hydrogenation of hindered ketones. Doubly α-branched ketones such as diisopropyl ketone was hydrogenated under nearly atmospheric conditions. Di-tert-butyl ketone could be hydrogenated under more forcing conditions.
Kawamorita, Soichiro,Hamasaka, Go,Ohmiya, Hirohisa,Hara, Kenji,Fukuoka, Atsushi,Sawamura, Masaya
supporting information; experimental part
p. 4697 - 4700
(2009/05/26)

Catalytic synthesis of oxygenate from alcohol
The present invention discloses a method for catalytic synthesis of oxygenate from alcohol. At first, a feeding material comprising at least one alcohol is provided. Next, a copper-containing catalyst is provided and the catalyst further comprises at least one metal element selected from the group consisting of the following: zinc, magnesium, and aluminum elements. Following that, a catalytic reaction of the feeding material over the copper-containing catalyst is carried out to synthesize at least one oxygenate.
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Page/Page column 4-8

(2008/06/13)

Impact of reaction products on the Grignard reaction with silanes and ketones
Grignard reactions with alkoxysilanes or carbonyl compounds produce alkoxymagnesium halides as by-products. Kinetic measurements for reactions of silanes and of a ketone were performed with Grignard reagents, enriched in alkoxymagnesium halides and taken in a great excess. The alkoxide-type reaction products complex tightly with Grignard reagents and enhance in this way their nucleophilicity, thus accelerating the reaction. However, alkoxides branched at α-C atom exert an unfavorable steric hindrance to reaction resulting in a decrease in the reaction rate.
Panov, Dmitri,Tuulmets, Ants,Nguyen, Binh T.
p. 4076 - 4079
(2007/10/03)

Stereoselection at the Steady State in Radical Cyclizations of Acyclic Systems Containing One Radical Acceptor and Two Precursors in a 1,5- Relationship under Pseudo-First-Order Conditions
The first example of a successive kinetic resolution of acyclic diastereomeric radical intermediates in a 1,5-relationship under pseudo-first-order conditions is reported. A mechanistic model involves nonselective generation of the radical intermediates followed by different partitioning of these between two different chemical pathways. The "2,5-cis" selectivity in the radical cyclization step arises from transition geometries with the substituents aligned in pseudoequatorial positions.
Andrukiewicz, Robert,Cmoch, Piotr,Gawel, Anna,Stalinski, Krzysztof
p. 1844 - 1848
(2007/10/03)

Reactions of aliphatic ketones R2CO (R = Me, Et, iPr, and tBu) with the MCl4/Li(Hg) system (M = U or Ti): Mechanistic analogies between the McMurry, Wittig, and Clemmensen reactions
Analysis of the products of the reactions of ketones R2CO (R = Me, Et, iPr, tBu) with the MCl4/Li(Hg) system (M = U, Ti) at 20°C revealed significant differences. For R = Me, the reaction proceeded exclusively (M = U) or preferentially (M = Ti) via a metallopinacol intermediate resulting from dimerization of ketyl radicals. Pinacol was liberated by hydrolysis, and tetramethylethylene was obtained after further reduction at 65°C. For R = iPr, formation of iPr2C=CiPr2 as the only coupling product, the nonproduction of this alkene by reduction of the uranium pinacolate [U]-OCR2CR2O-[U] (R = iPr) at 20°C, and the instability of the corresponding titanium pinacolate towards rupture of the pinacolic C-C bond indicated that reductive coupling of iPr2CO did not proceed by dimerization of ketyl radicals. Formation of 2,4-dimethyl-2-pentene was in favor of a carbenoid intermediate resulting from deoxygenative reduction of the ketyl. These results revealed that for sterically hindered ketones, McMurry reactions can be viewed as Wittig-like olefination reactions. For R = tBu, no coupling product was obtained and the alkane tBu2CH2 was the major product. The involvement of the carbenoid species [M]=CtBu2 was confirmed by its trapping with H2O, leading to tBu2CH2, and with the aldehydes RCHO, giving the cross-coupling products tBu2C=C(R)H (R = Me, tBu). Therefore, in the case of severely congested ketones, McMurry reactions present strong similarities to the Clemmensen reduction of ketones, owing to the involvement in both reactions of carbenoid species which exhibit similar reactivity. Wiley-VCH Verlag GmbH, 2001.
Villiers, Claude,Ephritikhine, Michel
p. 3043 - 3051
(2007/10/03)

Reactions of partially solvated Grignard reagents with a ketone
Ratios of the yields of addition and reduction products for the reactions of n-butylmagnesium chloride and bromide with diisopropyl ketone in toluene were determined at different THF, diethyl ether and methyl tertbutyl ether (MTBE) contents in the Grignard reagent. The reduction reaction yield is a maximum at the molar ratio 0.1 of THF or diethyl ether to the Grignard reagent. The addition reaction has a maximum in the region of 0.3-0.4 for the same ethers and about 1.5 for MTBE. The ratio Add/Red for conventional Grignard reagents is lower than that for partially solvated reagents. The results were discussed in terms of the solvation of the species in the reaction mixture. The decisive role of the steric requirements of the reagents over their intrinsic acid-base properties was demonstrated. Partially solvated Grignard reagents can serve as tools for the investigation of solvent effects in the Grignard reaction.
Tuulmets, Ants,Sassian, Meeri
p. 145 - 149
(2007/10/03)

New insights into the mechanism of the McMurry reaction
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Villiers, Claude,Ephritikhine, Michel
p. 2380 - 2382
(2007/10/03)

Hypervalent Iodine Oxidations: Structure and Kinetics of the Reactive Intermediates in the Oxidation of Alcohols and 1,2-diols by o-Iodoxybenzoic Acid (IBX) and Dess-Martin Periodinane. A Comparative 1H-NMR Study
Alcohols and 1,2-diols oxidation by o-iodoxybenzoic acid (IBX) has been examined by 1H-NMR spectroscopy.Reversible formation of reactive intermediates, iodic esters 5, has been observed, and their structures in DMSO-d6 solution have been defined as 10-I-4 axial alkoxyiodinane oxides by comparison of the chemical shift difference data with those obtained for Dess-Martin periodinane (DMP)-alcoholate and -diolate adducts.The dichotomous behaviour exhibited by IBX and DMP with 1,2-diols can be explained in terms of the different architecture of the reactive intermediates involved in the oxidation.With aliphatic alcohols, kinetic evidences support a two-step reaction mechanism involving a fast pre-equilibrium step leading to 5, followed by a rate-determining disproportionation step.With electronically activated benzyl alcohol, the attainment of pre-equilibrium is largely dependent on initial water concentration as a consequence of a particularly high K2 value.The influence of the alcohol structure on measured equilibrium (Keq) and rate constants (K2) and the effect of water on the overall reaction rate are discussed.
Munari, Sergio De,Frigerio, Marco,Santagostino, Marco
p. 9272 - 9279
(2007/10/03)

LiClO4-Promoted Addition of Alkyl Grignard and Alkynyllithium Reagents to Ketones. Comparison of a 5 M LiClO4/Diethyl Ether Solution with CeCl3
The influence of a 5 M ethereal LiClO4 solution as solvent on the addition of different alkyl Grignard and alkynyllithium reagents to highly enolizable ketones was studied.A comparison with the results in the presence of CeCl3 shows a similar improvement in the yield. - Keywords: Nucleophilic addition; Lewis acid; Enolizable ketones; Alkyl Grignard; Alkynyllithium reagent
Ipaktschi, Junes,Eckert, Thomas
p. 1171 - 1174
(2007/10/03)

- the Wet Chemical Route to a Highly Reactive Titanium Hydride
The reaction between catalytically prepared magnesium hydride (MgH2*) and in a molar ratio of 1.5:1 in THF yields a highly pyrophoric, X-ray amorphous titanium hydride precipitate with the composition (2).This novel titanium hydride precipitate with the composition (2).This novel titanium hydride has been characterized through hydrolysis and iodolysis, as well as through thermolysis to Ti* and H2 in the solid state and in organic solvents. 2 is slightly soluble in THF and proves itself as an active reagent in a variety of reactions. - Keywords: Magnesium Hydride, Titanium Hydride, McMurry-Reaction, Titanium
Becker, Beate,Bogdanovic, Borislav
p. 476 - 482
(2007/10/02)

Reduction of Alkyl Alkyl, Aryl Alkyl and Cyclic Ketones by Catalytic Hydrogen Transfer over Magnesium Oxide
The reduction of a series of alkyl alkyl, aryl alkyl and cyclic ketones by catalytic hydrogen transfer (CTR) from isopropyl alcohol over magnesium oxide has been investigated.CTR over MgO was found to be an effective and selective route to the corresponding methanols.At temperatures above 523 K parasubstituted phenylmethanols underwent consecutive dehydration leading to the formation of the corresponding styrene derivative with satisfying yields.These processes were studied in a flow system working continuously.A long-time stability of the catalyst activity has been demonstrated.
Kijenski, Jacek,Glinski, Marek,Czarnecki, Jacek
p. 1695 - 1698
(2007/10/02)

Reactions of Dialkylmagnesium-Salt Mixtures with Ketones: Increasing the Ratio of Addition to Reduction
The reduction of the ketone to a secondary alcohol that accompanies addition in reactions of ketones and dialkylmagnesium compounds can be lessened by first adding an appropriate salt to the dialkylmagnesium compound.With favorable salts and reactant stoichiometries, reduction is eliminated in reactions of dipropylmagnesium with diisopropyl ketone or di-tert-butyl ketone.In reactions of di-tert-butylmagnesium and di-tert-butyl ketone, reduction always predominates, although some addition does occur.Salts observed to have significant effects are potassium methoxide, (Me2NCH2)2CHOK, sodium methoxide, lithium methoxide, lithium tert-butoxide, tetrabutylammonium bromide, and benzyltriethylammonium chloride.Stoichiometry has significant effects on product composition, the least reduction product generally resulting when the ratio of salt to diorganomagnesium compound is at least one.The fundamental significance of the effects of stoichiometry and of the relative effects caused by different salts is obscured, however, by the heterogeneity of many of the systems.Magnesiate ions, such as (R2MgOMe)2 2-, are thought to be the organomagnesium species responsible for reactions that proceed without reduction.
Richey, Herman G.,DeStephano, Joseph P.
p. 3281 - 3286
(2007/10/02)

Reactions of Carbonyl Compounds with Grignard Reagents in the Presence of Cerium Chloride
The addition of Grignard reagents to ketones is significantly enhanced by cerium chloride with remarkable supression of side reactions, particularly enolization.Some esters, which are prone to side reactions, also react readily with Grignard reagents in the presence of cerium chloride to give normal reaction products in reasonable to high yields.
Imamoto, Tsuneo,Takiyama, Noboyuki,Nakamura, Kimikazu,Hatajima, Toshihiko,Kamiya, Yasuo
p. 4392 - 4398
(2007/10/02)

CLEAVAGE OF t-BUTYLDIMETHYLSILYL ETHER WITH t-BUTYL HYDROPEROXIDE AND DIOXOBIS(2,4-PENTANEDIONATO)MOLYBDENUM(VI) SYSTEM
A combination of t-butyl hydroperoxide (TBHP) and MoO2(acac)2 which is a mild epoxidation system, was found to be also effective for the cleavage of t-butyldimethylsilyl (TBDMS) ethers.
Hanamoto, Takeshi,Hayama, Takashi,Katsuki, Tsutomu,Yamaguchi, Masaru
p. 6329 - 6330
(2007/10/02)

The Predominance and Quantification of Steric Effects in the Solvolysis of Secondary Aliphatic Esters
The solvolysis rates of 35 tosylates in hexafluoroisopropyl alcohol are measured and compared to MM2 calculated strain energies, ΔSI, between weighted sp3 states and the lowest sp2 state.For unhindered (pseudo)equatorially substituted cycloalkyl tosylates a linear correlation, free from ambiguities involved, e.g., with the leaving group simulation, is obtained which shows a sensitivity of m=1.04+/-0.05, indicating an extremely late transition state or limiting behavior.Based on the corresponding equation, it is shown that alkyl substituents in the γ- and in the β-position do not promote significant rate increases, even when there is an antiperiplanar disposition between the leaving group and a migrating β-methyl substituent.Instead, these substituents can lead to substantial ΔG* increase (by up to 5 kcal/mol in comparison to the ΔSI prediction), which is related to steric hindrance of solvation and/or hindrance for elimination. 17-(Tosyloxy)androstanes show extremely large epimeric rate ratios of>30000; these are not due to anchimeric assistance but only to the exceedingly slow reaction of the hindered 17β isomer, whereas the fast reaction of the 17α tosylate (e.g. 200 times higher than cyclopentyl tosylate) is in line with the ΔSI calculation. endo-Bicycloheptane esters show evidence for steric hindrance; exo-norbornyl tosylate has, however, a ΔG* value lower by 4 kcal/mol than predicted. ks/kc values, obtained by rate comparison in 80percent ethanol and 97percent HFIP, vary between 0.5 and 300, mainly as a result of different steric hindrance to rearside nucleophilic subnstitution
Schneider, Hans-Joerg,Becker, Norman,Schmidt, Guenther,Thomas, Fred
p. 3602 - 3607
(2007/10/02)

CERIUM CHLORIDE-PROMOTED NUCLEOPHILIC ADDITION OF GRIGNARD REAGENTS TO KETONES AN EFFICIENT METHOD FOR THE SYNTHESIS OF TERTIARY ALCOHOLS
In the presence of anhydrous cerium(III) chloride, Grignard reagents react with ketones to afford addition products in high yields, even though the substrates are susceptible to abnormal reactions with Grignard reagents alone.
Imamoto, Tsuneo,Takiyama, Nobuyuki,Nakamura, Kamikazu
p. 4763 - 4766
(2007/10/02)

ORGANOMETALLIC CHEMISTRY UNDER HIGH PRESSURE: TRIALKYLTIN HYDRIDE ADDITION TO UNSATURATED SYSTEMS
The influence of high pressure (10-14 kbars) on the reaction of tin hydrides with alkenes and ketones has been investigated and a marked increase of yields generally was observed.For cyclopropyl- and cyclobutyl-alkenes, adducts were formed with retention of the rings.The stereochemical outcomes of the reaction were modified.
Rahm, A.,Castaing-Degueil, M.,Pereyre, M.
p. C29 - C32
(2007/10/02)

Photochemistry in solution-XX. Triplet reactivity of aliphatic aldehydes
The triplet self-quenching process of three aliphatic aldehydes has been investigated by inhibition with dienes (taking into account the singlet interaction with the dienes) and by laser flash photolysis. The results obtained for intersystem crossing, the setf-quenching process and product formation have been rationalized. The main reactivity observed for the three aldehydes is the self-quenching process which occurs from both the singlet and triplet state. The laser flash photolysis experiments carried out with butanal show two absorptions of a transient at 320 aod 355 nm; no evidence for two different species could be put forward. The similar decay of the two absorption maximas of the transient, as the concentration of aldehyde is increased, would be indicative of only one single absorbing species which could be either the triplet state of the aldehyde or a radical-pair formed by the self-quenching process or the 1,4-biradical resulting from γ-H abstraction. The fact that both the quenching experiments (by dienes or by 1-methylnaphthalene) and the laser flash measurements lead to about the same lifetime also indicates only one species. The products formed from the triplet setf-quenching process have also been obtained by a different method: excitation of benzophenone at 365 nm in the presence of butanal. The quantum yields for product formation is about the same as those obtained for the triplet by direct irradiation of butanal, except that of octane-4,5-dione which is increased if the photoreaction is carried out at 365 nm in the presence of beazophenone.
Kossanyi,Sabbah,Chaquin,Ronfart-Haret
p. 3307 - 3315
(2007/10/02)

Katalysatoraktivitaeten a, Gleichgewichte und Kinetik in den homogenen Bulk-H2-Transfer-Reaktionen als Funktion der H2-Donatoren und Acceptoren
Ketons are reduced under mild conditions to the corresponding alcohols by secondary alcohols in homogeneous bulk hydrogen transfer reactions, catalysed by Ru(CF3CO2)2CO(PΦ3)2.The reactions are reversible, the equilibrium constants vary from 0.1 to 21, and under optimized conditions time to establish equilibrium varies from 5 to 90 minutes at 140 deg C.The rate determining step seems to be the dehydrogenation of the alcohols.The conversion can be described by the rate law of a reversible second-order reaction.
Graser, Barbara,Strohmeier, Walter,Marcec, Radovan,Steigerwald, Hannelore
p. 671 - 677
(2007/10/02)