- Isothiourea-Catalyzed Acylative Kinetic Resolution of Tertiary α-Hydroxy Esters
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A highly enantioselective isothiourea-catalyzed acylative kinetic resolution (KR) of acyclic tertiary alcohols has been developed. Selectivity factors of up to 200 were achieved for the KR of tertiary alcohols bearing an adjacent ester substituent, with both reaction conversion and enantioselectivity found to be sensitive to the steric and electronic environment at the stereogenic tertiary carbinol centre. For more sterically congested alcohols, the use of a recently-developed isoselenourea catalyst was optimal, with equivalent enantioselectivity but higher conversion achieved in comparison to the isothiourea HyperBTM. Diastereomeric acylation transition state models are proposed to rationalize the origins of enantiodiscrimination in this process. This KR procedure was also translated to a continuous-flow process using a polymer-supported variant of the catalyst.
- Greenhalgh, Mark D.,Laina-Martín, Víctor,Neyyappadath, Rifahath M.,Qu, Shen,Smith, Andrew D.,Smith, Samuel M.
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supporting information
p. 16572 - 16578
(2020/09/09)
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- Selective Carbonyl?C(sp3) Bond Cleavage To Construct Ynamides, Ynoates, and Ynones by Photoredox Catalysis
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Carbon–carbon bond cleavage/functionalization is synthetically valuable, and selective carbonyl?C(sp3) bond cleavage/alkynylation presents a new perspective in constructing ynamides, ynoates, and ynones. Reported here is the first alkoxyl-radical-enabled carbonyl?C(sp3) bond cleavage/alkynylation reaction by photoredox catalysis. The use of novel cyclic iodine(III) reagents are essential for β-carbonyl alkoxyl radical generation from β-carbonyl alcohols, including alcohols with high redox potential (EoxP>2.2 V vs. SCE in MeCN). β-Amide, β-ester, and β-ketone alcohols yield ynamides, ynoates, and ynones, respectively, for the first time, with excellent regio- and chemoselectivity under mild reaction conditions.
- Jia, Kunfang,Pan, Yue,Chen, Yiyun
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supporting information
p. 2478 - 2481
(2017/02/23)
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- The cross-selective titanium(III)-catalysed acyloin reaction
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A titanium(iii)-catalysed intermolecular reductive coupling of ketones or imines with nitriles is described, which gives direct access to α-hydroxylated and α-aminated ketones. This coupling reaction is cross-selective and a catalytic version of the classical acyloin condensation. A reaction mechanism that is supported by first DFT calculations is discussed. the Partner Organisations 2014.
- Feurer, Markus,Frey, Georg,Luu, Hieu-Trinh,Kratzert, Daniel,Streuff, Jan
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supporting information
p. 5370 - 5372
(2014/05/06)
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- Highly efficient C-H hydroxylation of carbonyl compounds with oxygen under mild conditions
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A transition-metal-free Cs2CO3-catalyzed α-hydroxylation of carbonyl compounds with O2 as the oxygen source is described. This reaction provides an efficient approach to tertiary α-hydroxycarbonyl compounds, which are highly valued chemicals and widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very environmentally friendly and practical. This transformation is highly efficient and highly selective for tertiary C(sp3)-H bond cleavage. OH, so simple! A transition-metal-free Cs2CO 3-catalyzed α-hydroxylation of carbonyl compounds with O 2 provided a variety of tertiary α-hydroxycarbonyl compounds (see scheme; DMSO=dimethyl sulfoxide), which are widely used in the chemical and pharmaceutical industry. The simple conditions and the use of molecular oxygen as both the oxidant and the oxygen source make this protocol very efficient and practical.
- Liang, Yu-Feng,Jiao, Ning
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supporting information
p. 548 - 552
(2014/01/23)
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- A dinuclear palladium catalyst for α-Hydroxylation of carbonyls with O2
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A chemo- and regioselective α-hydroxylation reaction of carbonyl compounds with molecular oxygen as oxidant is reported. The hydroxylation reaction is catalyzed by a dinuclear Pd(II) complex, which functions as an oxygen transfer catalyst, reminiscent of an oxygenase. The development of this oxidation reaction was inspired by discovery and mechanism evaluation of previously unknown Pd(III)-Pd(III) complexes.
- Chuang, Gary Jing,Wang, Weike,Lee, Eunsung,Ritter, Tobias
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supporting information; experimental part
p. 1760 - 1762
(2011/04/15)
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- Oxidative cleavage of vicinal diols: IBX can do what Dess-Martin periodinane (DMP) can
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A study was conducted to demonstrate the similarity of reactivity between o-iodoxybenzoic acid (IBX), an oxidative agent of vicinal diols and Des-Martin periodinane (DMP). The study examined IBX-mediated oxidative cleavage of tert,tert-1,2-diols and discovered pathways that favored fragmentation of sec,sec-1,2-diols, which produce non-cleavage products. It was observed that IBX can be employed to perform oxidative cleavage of 1,2-diols similar to DMP by simple variation of solvent and temperature. It was also observed that protonation of 10-1-4 species of diols may suppress the nucleophilic attack, leading to the production of ketol to achieve oxidative cleavage of sec,sec-1,2-diols that yield non-cleavage products with IBX in DMSO. TFA was used as a significant source of protons and a better solvent of IBX to conduct protonation of diols. A variety of sec,sec,tert,tert and sec,tert syn-1,2-diols underwent oxidative cleavage effectively, using TFA as a solvent.
- Moorthy, Jarugu Narasimha,Singhal, Nidhi,Senapati, Kalyan
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p. 767 - 771
(2008/03/27)
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- Rhodium-catalyzed addition of arylstannanes to carbon-heteroatom double bond
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The addition of arylstannanes to the carbon-heteroatom double bond in the presence of a catalytic amount of a cationic rhodium complex ([Rh(cod)(MeCN)2]BF4) was examined. The reactions of aldehydes, α-dicarbonyl compounds, and N-substituted aldimines with the arylstannanes gave corresponding alcohols, α-hydroxy carbonyl compounds, and amines, respectively. An arylrhodium complex generated by the transmetalation with the arylstannane was probably the active catalytic species.
- Oi, Shuichi,Moro, Mitsutoshi,Fukuhara, Hiroe,Kawanishi, Takanori,Inoue, Yoshio
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p. 4351 - 4361
(2007/10/03)
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- Intramolecular and intermolecular ketone-ester reductive coupling reactions promoted by samarium(II) iodide
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Intramolecular and intermolecular ketone-ester reductive coupling reactions promoted by SmI2 have been studied. Substituted 2-hydroxy-5-ethoxycarbonylcyclopentanones, 5-ethoxycarbonylcyclopentenones and α-ketols were prepared in moderate to good yields at room temperature or under reflux under neutral conditions.
- Liu, Yunkui,Zhang, Yongmin
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p. 5745 - 5748
(2007/10/03)
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- Samarium(II) iodide-promoted intermolecular and intramolecular ketone- nitrile reductive coupling reactions
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Samarium (II) iodide, a strong one-electron transfer reducing reagent, has been successfully utilized for the intermolecular and intramolecular reductive coupling reactions of ketones with nitriles, α-Hydroxy ketones, monocyclic, fused bicyclic α-hydroxy ketones and monocyclic α-amino alcohols composed of a number of substitution patterns have been prepared in good yields at room temperature or reflux under neutral conditions. The procedure can avoid overreduction of the resulting of α-hydroxy ketones or α-amino alcohols. The crystal structures of monocyclic α-amino alcohols are reported.
- Zhou, Longhu,Zhang, Yongmin,Shi, Daqing
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- Samarium(II) iodide promoted novel reductive coupling reactions of ketones and nitriles
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The intramolecular and intermolecular reductive coupling reaction of ketones-nitriles promoted by SmI2 were studied.
- Zhou, Longhu,Zhang, Yongmin,Shi, Daqing
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p. 8491 - 8494
(2007/10/03)
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- The reduction of α-silyloxy ketones using phenyldimethylsilyllithium
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Phenyldimethylsilyllithium reacts with acyloin silyl ethers RCH(OSiMe3)COR 8 to give regiodefined silyl enol ethers RCH=C(OSiMe2Ph)R 9, and hence by hydrolysis ketones RCH2COR 10. The yields can be high but are usually moderate. The mechanism of this reduction is established to involve a Brook rearrangement (Scheme 6) rather than a Peterson elimination (Scheme 1). Although the mechanism appears to be the same in each case, the stereochemistries of the silyl enol ethers 9 are opposite in sense in the aromatic series (R = Ph, Scheme 7) and the aliphatic series (R = cyclohexyl, Scheme 8), with the major aromatic silyl enol ether being the thermodynamically less stable isomer E-PhCH=C(OSiMe2Ph)Ph E-9aa, and the major aliphatic silyl enol ether being the thermodynamically more stable isomer Z-c-C6H11CH= C(OSiMe2Ph)-c-C6H11 Z-9ba. This is a consequence of anomalous anti-Felkin attack in the aromatic series. The reaction with the silyl ether ButCH(OSiMe3)COPh 13b is normal in giving Z-ButCH= C(OSiMe2Ph)Ph Z-38 (Scheme 11), but reduction of the silyl ether 8a with lithium aluminium hydride is also anti-Felkin giving with high selectivity the meso diol PhCH(OH)CH(OH)Ph 39. The reaction between Phenyldimethylsilyllithium and the acyloin silyl ether 8d (R = But) does not give the ketone ButCH2COBut, but gives instead the anti-Felkin meso diol ButCHOHCHOHBut 40 also with high selectivity (Scheme 12). Silyllithium and some related reagents react with trifluoromethyl ketones 46 and 48 to give α,α-difluoro silyl enol ethers 47 and 49 (Scheme 14).
- Fleming, Ian,Roberts, Richard S.,Smith, Stephen C.
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p. 1215 - 1228
(2007/10/03)
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- Improved method for samarium diiodide induced reductive coupling reactions of acid halides
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Acid halides are known to be reductively coupled with aldehydes and ketones in the presence of samarium diiodide to generate α-hydroxy ketones. Low yields coupled product are obtained due to the competitive process of tetrahydrofuran attack on the acid chloride. This competitive reaction can be avoided and yields improved by preparation of samarium diiodide in acetonitrile.
- Ruder, Suzanne M.
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p. 2621 - 2624
(2007/10/02)
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- Photoalkylation of α-Diketones with Tetraalkylstannanes via Electron Transfer
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Irradiation of α-diketones in the presence of tetraalkylstannanes gave α-ketols via electron transfer.The analogy between the photo-induced electron transfer reactions and mass spectrometry exists in the fragmentation of the radical cation of the stannanes.
- Kyushin, Soichiro,Otani, Shinju,Takahashi, Tomoyuki,Nakadaira, Yasuhiro,Ohashi, Mamoru
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p. 775 - 778
(2007/10/02)
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- Process for the preparation of α-hdroxyketones
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A process for the preparation of α-hydroxyketones STR1 having a high purity in a good yield from a compound STR2 by rearrangement reaction in aqueous alkaline solution, where R1 and R3 each represent an alkyl, alkenyl or aryl group,
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- The Reaction of Benzil with Grignard Reagents
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Benzil reacts with Grignard reagents forming, in the first step, the 1,2-addition product (C-alkylation), but often also the 1,4-addition product (O-alkylation) and the reduction product, benzoin.The product distribution has been determined for mechanistic purposes for 16 Grignard reagents using a standard procedure.These results, and observations made using deuteriated reagents and the 5-hexenyl radical probe indicate an electron transfer (ET) mechanism for reagents having hydrogen in the β-position, while a polar mechanism is the most efficient for methyl, phenyl, benzyl and allyl Grignard reagents in the ether solution.For the ET mechanism, a six-centre transition state is suggested.Furthermore, a distinction is made between the primary cage product (O-alkyl) resulting from immediate combination of the radical pair, and the secondary cage product (C-alkyl) formed in the cage after rearrangement. 5-Hexenylmagnesium bromide yields uncyclised primary and secondary cage product, but also significant amounts of cyclised C-alkylation product formed by escape of the radicals from the cage and re-encounter after cyclisation of 5-hexenyl to cyclopentylmethyl.A recently suggested mechanism based on the existence of stable radical ion pairs is found to be unacceptable.
- Holm, T.
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p. 278 - 284
(2007/10/02)
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- Carbonylation of Aryl Halides and Vinyl Bromides Mediated by Tetracarbonylcobalt Anion
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The reaction of aryl halides (1a-g) with octacarbonyldicobalt in the presence of methyl iodide and sodium hydroxide under phase-transfer conditions was found to give a mixture of aryl methyl ketones (2a-g) and aromatic carboxylic acids (3a-h).From vinyl halides (9a-c), however, the corresponding carboxylic acids (10a-c) were obtained exclusively.
- Miura, Masahiro,Akase, Fumiaki,Shinohara, Masato,Nomura, Masakatsu
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p. 1021 - 1026
(2007/10/02)
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- Quasi-template Effect: a Tool for Controlling Stereochemistry in Acyclic Systems. Attempted Stereoselective Synthesis of α,α'-Dimethoxystilbene
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Alkylation with methyl tosylate of stilbenediol dianion, prepared in the reaction of benzoin with a series of alkali-metal hydroxides in THF, gave (E)- and (Z)-α,α'-dimethoxystilbenes as the major products in most cases, the E:Z ratio of which varies from 0.4 to 5.0 depending upon the alkali-metal cation employed; the results are rationalized in the quasi-template effect in an acyclic system and the hard-soft ion principle.
- Inoue, Yoshihisa,Ikeda, Hirokazu,Hakushi, Tadao
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p. 259 - 262
(2007/10/02)
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- Lithiation α to Heteroatoms: Eliminative Ring Fission of Heterocycles
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The behaviour of some heterocycles, having two heteroatoms in a 1,4-relationship, towards lithium diisopropylamide (LDA) has been examined.The dihydrobenzothiazines (2a-c) and (3b), morpholine (12), benzoxazine (14), oxathiane (16), piperazine (18), tetra
- Babudri, Francesco,Florio, Saverio,Reho, Antonia,Trapani, Giuseppe
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p. 1949 - 1955
(2007/10/02)
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- REACTIONS OF ACYL ANIONS GENERATED FROM ACID CHLORIDES AND DIIODOSAMARIUM
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Acid chlorides react with SmI2 to give α-diketones.Various experiments show that the initially formed acyl radical is rapidly transformed into an acyl anion which is thus generated by quite an unusual route.This species acylates acid chlorides, aldehydes and ketones in situ to give α-diketones and α-diketols.There are some limitations to this acyl anion chemistry but the reactions are realized with a good efficiency at room temperature in THF solution.
- Souppe, J.,Namy, J-L.,Kagan, H.B.
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p. 2869 - 2872
(2007/10/02)
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- Mechanism of Copper-Catalyzed Oxygenation of Ketones
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Deoxybenzoin (1) is converted by a Cu(II)-py-Et3N-MeOH-O2 (py=pyridine) system to a mixture of benzil (2), bidesyl (3), and the cleavage products PhCHO and PhCOOH.A product study comparing reactivities of 1 and 2 under identical conditions established (i) that the conversion of 1 to 3 is effected by Cu(II) alone, (ii) that PhCHO is generated only from 1, in a reaction that requires both Cu(II) and O2, and (iii) that 2 undergoes C-C cleavage only in the presence of H2O, forming PhCOOH exclusively, in a reaction that requires Cu(II) but not O2. α-Methyldeoxybenzoin (5) undergoes an exceptionally slow but similar reaction ( giving the tertiary α-ketol 6 rather than diketone 2).Mechanisms for these reactions are presented, and the significance of the results is discussed.
- Sayre, L. M.,Jin, S.-J.
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p. 3498 - 3503
(2007/10/02)
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- α-Heterosubstituted Phosphonate Carbanions. 11. Benzoins via an Acyl Anion Equivalent. Novel One-Pot Preparation of Benzofurans via Benzoins Using Hydriodic Acid
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Diethyl 1-(trimethylsiloxy)-1-phenylmethanephosphonate carbanion 2 is introduced as a novel acyl anion equivalent.When 2 reacts with aldehydes or ketones, a 1,4 oxygen-oxygen silicon migration with subsequent loss of diethyl lithium phosphite is observed.An efficient method utilizing 2 for the preparation of otherwise difficultly obtainable substituted benzoins is presented.Also a novel one-pot method which offers a facile entry into the 2-phenylbenzofuran ring system from 2 via benzoin intermediates using hydriodic acid was developed.
- Koenigkramer, Rusty E.,Zimmer, Hans
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p. 3994 - 3998
(2007/10/02)
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- α-HETEROSUBSTITUTED PHOSPHONATE CARBANIONS IX : DIETHYL 1-PHENYL-1-TRIMETHYLSILOXYMETHANE PHOSPHONATE AS AN ACYL ANION EQUIVALENT; A NOVEL METHOD FOR THE PREPARATION OF α-HYDROXYKETONES.
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Diethyl 1-phenyl-1-trimethylsiloxymethane phosphonate carbanion was found to react as an effective acyl anion equivalent in the preparation of α-hydroxy ketones from aliphatic and aromatic aldehydes and ketones.A 1,4-oxygen-oxygen silicon migration was also observed.
- Koenigkramer, Rusty E.,Zimmer, Hans
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p. 1017 - 1020
(2007/10/02)
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- α-(Cyanoethyl)-benzoin ethers
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The invention relates to racemates of the formula (I) SPC1 in which R1 and R2 are hydrogen, lower alkyl, methoxy, ethoxy or halogen, R3 is unsubstituted alkyl or lower alkyl substituted with alkoxy carbonyl carbonamido, cyano or hydroxyl or unsubstituted alkenyl or alkenyl substituted with halogen or halogen-, methyl-, ethyl-, methoxy- or ethoxy-substituted phenyl or unsubstituted cycloalkyl or cycloalkyl substituted with lower alkyl or unsubstituted phenylalkyl or phenylalkyl, the phenyl nucleus of which being substituted with methyl, methoxy, halogen or nitro, and R4 is unsubstituted alkyl or alkenyl or unsubstituted cycloalkyl or cycloalkyl substituted with lower alkyl or unsubstituted phenyl or phenyl substituted with lower alkyl methoxy, ethoxy or halogen or unsubstituted phenylalkyl or phenylalkyl, the phenyl nucleus of which being substituted with methyl, methoxy or halogen and X is oxygen or sulphur, Which are useful as photosensitizers for light induced polymerisations of vinyl monomers as well as for the light induced crosslinking of unsaturated polycondensates and polymers.
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