- Fluorous, Chromatography-Free Mitsunobu Reaction
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(Matrix Presented) The reaction of secondary and primary alcohols with highly fluorinated 3,4,5-tris(5,5,6,6,7,7,8,8,9,9,10,10,11,11,12,12,12-heptadecafluorododecan-1- yloxy)benzoic acid in the presence of Ph3P and DIAD in THF at room temperature (fluorous Mitsunobu) resulted in a simple, chromatography-free isolation protocol with excellent yields (83-96%).
- Markowicz, Marcin W.,Dembinski, Roman
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- Method for synthesizing cholesterol by taking BA as raw material
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The invention discloses a method for synthesizing cholesterol by taking BA as a raw material. A plant source raw material 21-hydroxy-20-methylpregna-4-en-3-one, also known as Shuangjiangchun or BA is taken as a raw material, and the cholesterol is synthesized by the steps of oxidation, Wittig reaction, acetylation, reduction, selective hydrogenation reduction and the like. The raw materials for synthesizing cholesterol are plant sources, the price is low, the safety is high, the risk of pathogenic bacteria and virus infection is avoided, and the synthesis method is easy to operate, high in yield, few in side reaction, environmentally friendly, good in economical efficiency and convenient for industrial production; and the invention solves the safety problem of the existing cholesterol product and the problems of high cost, environmental unfriendliness and unsuitability for large-scale industrial production in the synthesis technology.
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- Electrochemical Borylation of Alkyl Halides: Fast, Scalable Access to Alkyl Boronic Esters
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Herein, a fast, scalable, and transition-metal-free borylation of alkyl halides (X = I, Br, Cl) enabled by electroreduction is reported. This process provides an efficient and practical access to primary, secondary, and tertiary boronic esters at a high current. More than 70 examples, including the late-stage borylation of natural products and drug derivatives, are furnished at room temperature, thereby demonstrating the broad utility and functional-group tolerance of this protocol. Mechanistic studies disclosed that B2cat2 serves as both a reagent and a cathodic mediator, enabling electroreduction of difficult-to-reduce alkyl bromides or chlorides at a low potential.
- Cao, Yangmin,Hu, Ping,Huang, Cheng,Liu, Zhao,Lu, Qingquan,Ma, Wan,Peng, Pan,Qi, Xiaotian,Wang, Bingbing
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supporting information
p. 12985 - 12991
(2021/09/03)
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- Radical chain reduction of alkylboron compounds with catechols
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The conversion of alkylboranes to the corresponding alkanes is classically per-formed via protonolysis of alkylboranes. This simple reaction requires the use of severe reaction conditions, that is, treatment with a carboxylic acid at high temperature (>150 °C). We report here a mild radical procedure for the transformation of organoboranes to alkanes. 4-tert-Butylcatechol, a well-established radical inhibitor and antioxidant, is acting as a source of hydrogen atoms. An efficient chain reaction is observed due to the exceptional reactivity of phenoxyl radicals toward alkylboranes. The reaction has been applied to a wide range of organoboron derivatives such as B- alkylcatecholboranes, trialkylboranes, pinacolboronates, and alkylboronic acids. Furthermore, the so far elusive rate constants for the hydrogen transfer between secondary alkyl radical and catechol derivatives have been experimentally determined. Interestingly, they are less than 1 order of magnitude slower than that of tin hydride at 80 °C, making catechols particularly attractive for a wide range of transformations involving C-C bond formation.
- Villa, Giorgio,Povie, Guillaume,Renaud, Philippe
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supporting information; experimental part
p. 5913 - 5920
(2011/06/16)
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- A simple and efficient catalytic method for the reduction of ketones
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A range of ketones was efficiently reduced in the presence of catalytic amounts of lithium isopropoxide in 2-propanol under microwave heating, with alcohol products being formed in yields up to 99%.
- Ekstroem, Jesper,Wettergren, Jenny,Adolfsson, Hans
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p. 1609 - 1613
(2008/02/11)
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- 2-(Prenyloxymethyl)benzoyl (POMB) group: a new temporary protecting group removable by intramolecular cyclization
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2-(Prenyloxymethyl)benzoates can be prepared from alcohols and readily available 2-(prenyloxymethyl)benzoic acid by standard acylation techniques or by Mitsunobu reaction with inversion of configuration. The POMB group can be cleaved first by oxidative removal of the prenyl group with DDQ followed by lactonization with expulsion of the alcohol catalyzed by Yb(OTf)3. These reaction conditions are compatible with the presence of a large number of common protecting groups.
- Vatèle, Jean-Michel
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p. 10921 - 10929
(2008/02/12)
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- The effects of added ammonium chloride in the reductive amination of some carbonyl compounds over Ru and Pd catalysts
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The reductive amination of acetophenone, (+)-camphor, and 5α-cholestan-3-one over Ru and Pd metals as well as their carbon-supported catalysts gave corresponding amines together with alcohols as by-products. However, we found that the corresponding amines are selectively synthesized by the addition of ammonium chloride to the reaction system with depression of the formation of alcohol, as exemplified with acetophenone. Although alcohols are usually not formed over Pd with alicyclic ketones, the alcohols formation was effectively depressed over Ru in the presence of ammonium chloride. The effects of the additive on the stereoselectivity of the formation of amines are also discussed in the cases of (+)-camphor and 5α-cholestan-3-one.
- Ikenaga, Tomoaki,Matsushita, Kumiko,Shinozawa, Junichi,Yada, Satoru,Takagi, Yuzuru
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p. 2105 - 2109
(2007/10/03)
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- Al-isopropoxydiisobutylalane: A study of the effect of solvent on the rate and stereoselectivity of cyclic ketone reduction
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The effect of solvent on the rate and stereoselectivity of cyclic ketone reduction by Al-isopropoxydiisobutylalane (DIBAiOPr) has been investigated. In dichloromethane, DIBAiOPr behaves as a bulky reducing agent, approaching the carbonyl group along an equatorial trajectory to produce the axial alcohol with > 10:1 stereoselectivity. In sharp contrast, reduction in toluene gives the complementary outcome, affording the thermodynamically more stable isomer with > 99:1 stereoselectivity.
- Bahia, Perdip S.,Jones, Matthew A.,Snaith, John S.
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p. 9289 - 9291
(2007/10/03)
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- A free radical method for reduction of cyclohexanones - Preferential formation of equatorial alcohols
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Cyclohexanones react with 2-hydroselenobenzoic acid to afford spiro-[4H-3,1-benzoxaselenin-2,1′-cyclohexan]-4-ones. Stannane reduction and basic hydrolysis gives epimeric cyclohexanols, with the equatorial isomer predominating.
- Clive, Derrick L. J.,Cheng, Hua
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p. 1951 - 1961
(2007/10/03)
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- Cleavage of a p-cyanobenzyl group from protected alcohols, amines, and thiols using triethylgermyl sodium
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Alcohols, amines, and thiols protected with a p-cyanobenzyl group can be easily and quantitatively deprotected using triethylgermyl sodium under mild conditions.
- Yokohama, Yasuo,Takizawa, Shuichi,Nanjo, Masato,Mochida, Kunio
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p. 1032 - 1033
(2007/10/03)
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- Collisionally-induced dissociation mass spectra of organic sulfate anions
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The collisionally-induced dissociation mass spectra of a variety of organic sulfate ester anions are described and mechanistically rationalized. A cyclic syn-elimination pathway, analogous to that of the Cope elimination, is postulated for the commonly observed formation of bisulfate anion (HSO4-, m/z 97). Deuterium labeling experiments confirm that the proton transferred to oxygen during bisulfate elimination normally originates from the C-2 position, although examination of the spectra of polyfunctional steroids reveals that the proton abstracted may originate from more distant sites as well. Adamantyl, phenyl, and vinyl sulfate anions, which do not readily lend themselves to a cyclic syn-elimination, do not give rise to an m/z 97 ion. Instead, these sulfates undergo both heterolytic and homolytic S-O bond cleavages to yield an m/z M - 80 anion, resulting from loss of neutral SO3, as well as an ion at m/z 80, corresponding to SO3-·, respectively. Sulfates that can give rise to a resonance stabilized radical by homolytic C-O bond fission, as exemplified by benzyl and linalyl sulfates, can be recognized by the formation of an m/z 96 (SO4-·) ion.
- Attygalle,Garcia-Rubio,Ta,Meinwald
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p. 498 - 506
(2007/10/03)
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- Acceleration of the reduction of aldehydes and ketones using Mn(dpm)3 catalyst and phenylsilane in the presence of dioxygen
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Saturated ketones and aldehydes are reduced to alcohols by phenylsilane and Mn(dpm)3(cat) in the presence of dioxygen.
- Magnus, Philip,Fielding, Mark R
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p. 6633 - 6636
(2007/10/03)
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- Phosphine effects in the copper(I) hydride-catalyzed hydrogenation of ketones and regioselective 1,2-reduction of α,β-unsaturated ketones and aldehydes. Hydrogenation of decalin and steroidal ketones and enones
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The stereoselectivity and regioselectivity of the catalytic hydrogenation of ketones and α,β-unsaturated ketones and aldehydes using soluble copper(I) hydride catalysts have been investigated as a function of the ancillary phosphine ligand. While a relatively narrow range of aryldialkylphosphine ligands produce active hydrogenation catalysts, some ligands provide higher selectivity for 1,2-reduction of acyclic unsaturated carbonyl substrates than observed using the previously reported dimethylphenylphosphine-stabilized catalyst. The synthetic utility of this class of hydridic hydrogenation catalysts is illustrated by the hydrogenation of decalin and steroidal ketones and enones, the latter giving allylic alcohols with high selectivity. (C) 2000 Elsevier Science Ltd.
- Chen, Jian-Xin,Daeuble, John F.,Stryker, Jeffrey M.
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p. 2789 - 2798
(2007/10/03)
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- The reaction of alkyl peroxy radicals
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Secondary alkyl peroxy radicals generated from 4-phenyl-2-butyl-, 2-nonyl- and 3α-cholestanyl hydroperoxides at 45°C undergo Russell termination reactions in preference to non-terminating decomposition reactions. Non-terminating decomposition of 2-nonyl peroxy radicals afforded 2,5-nonanedione and 2,5-nonanediol due to intramolecular hydrogen abstraction reactions of alkoxy radicals. The radicals derived from 2-methyl-4-phenyl-2-butyl-, 2-methyl-5-phenyl-2-pentyl- and 2-methyl-6-phenyl-2-hexyl hydroperoxides afforded benzylic functionalized products due to intermolecular reactions. 2-Hexylperoxy radicals generated in excess alcohols ineffectively abstracted the α-hydrogens of alcohols. These results demonstrate the low reactivity of alkyl peroxy radicals.
- Goosen, Andre,Kindermans, Sybrandus
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- Potassium borohydride reductions of immobilised ketosteroids
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Ketosteroids absorbed into various insoluble supports (powdered polyethylene, microporous 2% crosslinked polystyrene beads, macroporous highly crosslinked polystyrene beads, silica gel and alumina) call be reduced using aqueous potassium barohydride. The use of phase transfer catalysts generally raises yields. In the case of 6-ketosteriods the supported reactions often follow a stereochemical course significantly different from that of analogous reactions in solution. This is attributed to the adsorbtion of the steroid onto the inner surfaces of the supports. In these cases reduction of (he ketosteroid by alkoxyborohydrides is substantially suppressed and thus most of the reduction is brought about by BH4- itself, a relatively sterically undemanding reductant. The net result is that whilst reductions of 6-ketosteroids in solution by potassium borohydride typically gives the 69α- and 6β-alcohols in the ratio 15:85, with the supported steroid the ratios can be as high as 90:10.
- Briggs, Josie C.,Hodge, Philip,Zhengpu, Zhang
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p. 3943 - 3956
(2007/10/03)
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- Efficient method for inversion of secondary alcohols by reaction of chloromethanesulfonates with cesium acetate
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Inversion of a variety of secondary alcohols using the (chloromethylsulfonyl)oxy group as a favorable leaving group with cesium acetate in the presence of 18-crown-6 has been performed to give the inverted acetates in high yields.
- Shimizu, Takeshi,Hiranuma, Sayoko,Nakata, Tadashi
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p. 6145 - 6148
(2007/10/03)
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- Formation of ketones from alkyl nitrites in the solid state
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Alkyl nitrites selectively afforded the corresponding ketones upon photoirradiation in the solid state. It was suggested by the X-ray crystallographic analysis that the cavity in crystal and the initial conformation of the nitroso group had an influence on the yield of the ketones.
- Kinbara, Kazushi,Takezaki, Hiroshi,Kai, Akiyoshi,Saigo, Kazuhiko
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p. 217 - 218
(2007/10/03)
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- Mechanism of cholesterol reduction to coprostanol by Eubacterium corpostanoligenes ASTCC 51222
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The mechanism of reduction of cholesterol to coprostanol by Eubacterium coprostanoligenes ATCC 51222 was studied by incubating the bacterium with a mixture of α- and β-isomers of cholesterol.Coprostanol, isolated after incubation of cholesterol in a growth medium under anaerobic conditions, retained 97percent of the tritium originally presented in cholesterol.The majority of this tritium (64percent), however, was in the C-6 position in coprostanol, which showed that the conversion of cholesterol into coprostanol by E. coprostanoligenes involved the intermediate formation of 4-cholesten-3-one followed by the reduction of the latter to coprostanol.In resting cell assays in which washed bacterial cells were incubated with micellar cholesterol in phosphate buffer at 37 deg C, both 4-cholesten-3-one and coprostanone were produced in addition to coprostanol.Furthermore, 5-cholesten-3-one, 4-cholesten-3-one, and coprostanone were converted efficiently to coprostanol by E. coprostanoligenes.These results support the hypothesis that the major pathway for reduction of cholesterol by E. coprostanoligenes involves the intermediate formation of 4-cholesten-3-one followed by reduction of the latter to coprostanol through coprostanone as an intermediate. (Steroids 61:33-40, 1996) - Key words: dual-labeled cholesterol, coprostanol; cholesterol reduction; Eubacterium; NMR.
- Ren, Dewei,Li, Ling,Schwabacher, Alan W.,Youbg, Jerry W.,Beitz, Donald C.
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- Electrochemical preparation and some reactions of alkoxy triphenylphosphonium ions
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The formation of an alkoxy triphenylphosphonium ion by anodic oxidation of Ph3P in the presence of an alcohol was investigated. When a CH2Cl2 solution of Ph3P, Ph3P-H·ClO4-, and an alcohol was subjected to constant-current electrolysis in an undivided cell equipped with a graphite anode and a Pt cathode, the 31P-NMR spectra of the resulting electrolyte showed that alkoxy triphenylphosphonium perchlorates (2) were formed in good to fair yields from primary and secondary aliphatic alcohols, while allylic and bencyclic alcohols were transformed to the corresponding alkyl phosphonium ions, and in the case of tertiary aliphatic alcohols, no formation of the corresponding alkoxy or alkyl phosphonium ions was recognized at all. The isolation of 2 thus formed was achieved in good yields by a simple procedure. For the electrolysis, Ph3P+H·BF4- could be utilized instead of the perchlorate salt, giving an alkoxy triphenylphosphonium tetrafluoroborate (3) from primary and secondary aliphatic alcohols. The reaction of the alkoxy phosphonium ion prepared from β- and α-cholestanol with various nucleophiles such as Bu4N+·X- (X = Br, Cl, F, N3, SCN), PhSH, and PhOH was examined. The results indicated that the reaction site of the phosphonium ions is dictated by the identity of the nucleophile. A soft nucleophile was apt to attack at the α-carbon, giving the corresponding SN2 reaction product in a good yield, while a hard one tended to react at the phosphorus of the phosphonium ion, leading to the regeneration of the cholestanol.
- Maeda,Koide,Maki,Ohmori
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p. 1076 - 1080
(2007/10/02)
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- Stereoselective Introduction of Hydroxyl Groups via Hydrazones
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Reduction of tosylhydrazones by hydride reagents in wet alcohol gave predominantly alcohols whose stereochemistries are opposite to those of the major reduction products of the corresponding ketones with sodium borohydride.
- Tada, Masahiro,Chiba, Kazuhiro,Izumiya, Koji,Tamura, Mihoko
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p. 3532 - 3533
(2007/10/02)
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- Cerium(IV)-Mediated Synthesis of Tetrahydrofuranyl Ethers
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The reaction of tetrahydrofuran with an alcohol in the presence of ceric triethylammonium nitrate provides a convenient and general procedure for protecting the hydroxyl function.Tetrahydrofuranyl ethers of primary, secondary and tertiary alcohols were obtained in good yields.
- Maione, Anna M.,Romeo, A.
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p. 250 - 251
(2007/10/02)
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- STUDIES ON THE CHEMO- AND STEREOSELECTIVITY OF SODIUM BOROHYDRIDE-POLYETHYLENE GLYCOL 400-MEDIATED REDUCTIONS
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Chemo- and stereoselectivity of reductions by the NaBH4/polyethylene glycol (PEG) 400 system have been studied and compared to the traditional NaBH4 reductions in methanol.When the stereoselectivity was tested on 3- and 7-keto steroids 1a and 1b, respectively, interesting improvements were observed.Aldehydes were reduced faster than ketones and in the case of 3-oxo-pregn-4-en-20β-carboxaldehyde, 2a, the aldehyde was reduced completely leaving the unsatured ketone moiety unchanged.Absorption on inorganic support or addition of a few cationic species led to inactive or much less active reducing species.
- Santaniello, Enzo,Ferraboschi, Patrizia,Fiecchi, Alberto,Grisenti, Paride,Manzocchi, Ada
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p. 701 - 704
(2007/10/02)
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- The Stereochemistry of Organometallic Compounds. XXV The Stereochemistry of Displacements of Secondary Methanesulfonate and p-Toluenesulfonate Esters by Diphenylphosphide Ions. X-Ray Crystal Structure of (5α-Cholestan-3α-yl)diphenylphosphine Oxide
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Reactions of both axial and equatorial cholestan-3α- and -3β-yl mesylates and tosylates with sodium diarylphosphides give cholestanylphosphines in good yield and with complete inversion of stereochemistry.The stereochemistry has been established by an X-ray crystal structure of (5α-cholestan-3α-yl)diphenylphosphine oxide, and a general method for distinguishing between axial and equatorial phosphines based on 31P n.m.r. spectra is presented.The monophosphines were used as ligands in asymmetric hydrogenation, but only low optical yields were obtained.
- Jackson, W. Roy,Thomson, Robin J.,Mackay, Maureen F.
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p. 111 - 118
(2007/10/02)
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- Action des metaux sur les esters carboxyliques en presence d'hexamethylphosphortriamide: une methode simple et efficace de reduction des alcools en alcanes
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Carboxylic acids, alcohols (R'OH), and alkanes (R'H) are the main products of the reduction of carboxylic esters (RCO2R') by sodium in hexamethylphosphoric triamide (HMPA).Alkanes are preferentially formed from the carboxylic esters of hindered alcohols.The alkane content, however, is lowered when there is less steric hindrance on the carboxylic group, and increased when tert-butanol is introduced into the reaction mixture.The reduction of esters in HMPA has been compared to the reduction in alkylamines.The alkane is produced mainly by the decomposition of a radical anion intermediate which can be solvated by HMPA.The alcohol is the result of several possible bimolecular nucleophilic reactions; however, unimolecular and bimolecular processes are involved in the production of the carboxylic acid.
- Deshayes, Henri,Pete, Jean-Pierre
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p. 2063 - 2072
(2007/10/02)
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- STEREOCHIMIE-LII. CONTROLE ORBITALAIRE DE LA STEREOCHIMIE DES REACTIONS-III EFFETS DES GROUPES β-FLUORO ET β-CYANO SUR LA STEREOCHIMIE ET LA CINETIQUE DE LA REDUCTION DE CYCLOHEXANONES PAR LE TRITERTIOBUTOXYALUMINOHYDRURE DE LITHIUM
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The respective influences of β-fluoro and β-cyano groups on the reduction of ketones by Li(t-BuO)3AlH on the stereoselectivities of the reduction with and without added cryptands, and with and without added alkyl fluoride and nitrile, were compared with ab initio calculations using the frontier orbitals of analogous carbonyl compounds to give energy values
- Agami, C.,Kazakos, A.,Levisalles, J.,Sevin, A.
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p. 2977 - 2981
(2007/10/02)
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- Stereocontrolled catalytic hydrogenations of 3-oxocholestanes and some related compounds to the corresponding axial 3-alcohols
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Catalytic hydrogenations of 5α-cholestan-3-ones and related compounds with Urushibara nickel A catalyst in cyclohexane gave a distinct preponderance of unstable axial 3α-ols.Product ratios of axial alcohols decreased with increasing solvent polarity.For 3-oxo-5α-steroids, the cobalt catalyst was less selective for the axial alcohol formation.On the other hand, conversion of 5β-cholestan-3-one into the corresponding axial 3β-ol was most successfully attained by hydrogenation catalyzed by Urushibara cobalt A catayst in methanol.For such a 5β-ketone, alcoholic media with higher polarities were more favorable for giving the product rich in axial alcohol.The stereochemistry of the products obtained from hydrogenations conducted in nonpolar solvents may be understood in terms of steric congestion around the ketone carbonyl group.However, when alcohols were used as solvents, the product ratios obtained did not correlate well with the congestion ratios of substrates.
- Ishige, Masayoshi,Shiota, Michio
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p. 1061 - 1068
(2007/10/02)
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- Activation of Reducing Agents. Sodium Hydride Containing Complex Reducing Agents. 13. Selective Heterogeneous Hydrogenation of Polyfunctional Substrates over Nic
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Preparative-scale heterogeneous hydrogenation over Nic at room temperature and 1 atm are described.It is shown that these catalysts allow the selective hydrogenation of carbon-carbon double bonds in the presence of oxo groups without side reactions.Alkynes and functional alkynes are selectively hydrogenated to the corresponding cis alkenes in high yields.Carbonyl group hydrogenations were also performed in high yields.Selective hydrogenation properties of Nic were exemplified in the steroid series.Finally, it was demonstrated that this new catalyst-preparation concept is not limited to nickel and also applies to the preparation of cobalt and palladium catalysts.
- Gallois, Philippe,Brunet, Jean-Jaques,Caubere, Paul
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p. 1946 - 1950
(2007/10/02)
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- Kinetics and Activation Parameters for the Reduction of Alkylcyclohexanones by Lithium Tri-tert-butoxyaluminohydride
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The kinetics of reduction of 15 cyclohexanones by lithium tri-tert-butoxyaluminohydride in tetrahydrofuran solvent are reported.The data confirm that the reaction is well represented by a simple second-order kinetic process.Second-order rate constants determined at various temperatures are recorded and the activation parameters determined.Rate constants vary from 5.0E-3 to 4.4 l mol-1 s-1; these rate constants exceed those of reduction by NaBH4 by factors varying from 50 (unhindered cyclohexanones) to 450 (hindered cyclohexanones).The reductions appear to be nearly isoenthalpic, all but three of the values of ΔH(excit.) being in the range 6.8 +/- 0.8 kcal mol-1.Variations in rates between ketones are caused by changes in ΔS(excit.), and entropy is also more significant than enthalpy in the free-energy barrier to reaction.Mechanistic aspects of the reduction are discussed.
- Wigfield, Donald C.,Gowland, Frederick W.
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p. 653 - 658
(2007/10/02)
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