- Enantioselective Acyloin Rearrangement of Acyclic Aldehydes Catalyzed by Chiral Oxazaborolidinium Ion
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A catalytic enantioselective acyloin rearrangement of acyclic aldehydes to synthesize highly optically active acyloin derivatives is described. In the presence of a chiral oxazaborolidinium ion catalyst, the reaction provided chiral α-hydroxy aryl ketones in high yield (up to 95%) and enantioselectivity (up to 98% ee). In addition, the enantioselective acyloin rearrangement of α,α-dialkyl-α-siloxy aldehydes produced chiral α-siloxy alkyl ketones in high yield (up to 92%) with good enantioselectivity (up to 89% ee).
- Cho, Soo Min,Lee, Si Yeon,Ryu, Do Hyun
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supporting information
p. 1516 - 1520
(2021/03/03)
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- Synthesis of unsymmetrical benzilsviapalladium-catalysed a-arylation-oxidation of 2-hydroxyacetophenones with aryl bromides
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A diverse set of unsymmetrically substituted benzils were facilely synthesised by a cross-coupling reaction between 2-hydroxyacetophenones and aryl bromides in the presence of a palladium catalyst. Experimental studies suggested a reaction mechanism involving a one-pot tandem palladium-catalysed a-arylation and oxidation, where aryl bromides play a dual role as mild oxidants as well as arylating agents.
- Matsuda, Takanori,Oyama, Souta
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supporting information
p. 3679 - 3683
(2020/06/03)
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- Green preparation method α - hydroxyketone
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The invention relates to a green preparation method of alpha-hydroxyketone. The method comprises the following steps: adding ketone, iodine, 1,4-diazabicyclo[2.2.2]octane and methanol into a glass reaction bottle in sequence; then stirring and reacting for 14 to 30h at room temperature in an air atmosphere under the irradiation of a 23W compact type fluorescent lamp, so as to obtain a reaction mixture; carrying out silica gel column chromatographic separation to obtain the pure alpha-hydroxyketone. The green preparation method provided by the invention has the characteristics of greenness, high efficiency, simplicity in operation, moderate conditions, wide applicability and easiness for industrialization.
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Paragraph 0091-0094
(2020/08/27)
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- Mechanism of α-ketol-type rearrangement of benzoin derivatives under basic conditions
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The mechanism of base-catalyzed rearrangement of ring-substituted benzoins in aqueous methanol was examined by kinetic and product analyses. Substituent effects on the rate and equilibrium constants revealed that the kinetic process has a different electron demand compared to the equilibrium process. Reactions in deuterated solvents showed that the rate of H/D exchange of the α-hydrogen is similar to the overall rate toward the equilibrium state. A proton-inventory experiment using partially deuterated solvents showed a linear dependence of the rate on the deuterium fraction of the solvent, indicating that only one deuterium isotope effect contributes to the overall rate process. All these results point to a mechanism in which the rearrangement is initiated by the rate-determining α-hydrogen abstraction rather than a mechanism with initial hydroxyl hydrogen abstraction as in the general α-ketol rearrangement.
- Karino, Masahiro,Kubouchi, Daiki,Hamaoka, Kazuki,Umeyama, Shintaro,Yamataka, Hiroshi
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p. 7194 - 7198
(2013/08/23)
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- (S)-Mandelic acid enolate as a chiral benzoyl anion equivalent for the enantioselective synthesis of non-symmetrically substituted benzoins
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A strategy for the enantioselective synthesis of non-symmetrically substituted benzoins from (S)-mandelic acid and aromatic aldehydes has been developed. This strategy is based on a diastereoselective aldol reaction of the lithium enolate of the 1,3-dioxo
- Blay, Gonzalo,Fernández, Isabel,Monje, Belén,Montesinos-Magraner, Marc,Pedro, José R.
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experimental part
p. 881 - 890
(2011/03/19)
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- Enantioselective synthesis of unsymmetrical benzoins from (S)-mandelic acid enolate and aromatic aldehydes
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Highly enantioenriched unsymmetrical benzoins are obtained from (S)-mandelic acid. The reaction of the lithium enolate of the 1,3-dioxolan-4-one derived from optically active (S)-mandelic acid and pivalaldehyde with aromatic aldehydes proceeds readily to
- Blay, Gonzalo,Fernández, Isabel,Monje, Belén,Pedro, José R.
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p. 8039 - 8042
(2007/10/03)
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- Samarium reagent-promoted formation of benzoins from diarylmethanones and DMF via a carbene rearrangement reaction
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Prompted by samarium metal in DMF with TMSCl or iodine as an activator, or by SmI2/THF system, diarylmethanones react readily with DMF to afford benzoins in moderate to good yields via rearrangement of aryl groups. As for asymmetric diarylmethanones, products resulting from the migration of either aryl group were obtained, where the migration of aryl groups shows certain priority.
- Liu, Yongjun,Xu, Xiaoliang,Zhang, Yongmin
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p. 4867 - 4873
(2007/10/03)
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- Direct Formation of Benzoins from Diarylmethanones via a Rearrangement Reaction Promoted by Samarium Metal in DMF
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Diarylmethanones react readily with DMF when promoted by samarium metal in DMF with TMSCl or iodine as an activator, to afford benzoins in good to excellent yields via rearrangement of aryl groups. As for asymmetric diarylmethanones, products resulting from the migration of either aryl group were obtained, where the migration of aryl groups shows certain priority.
- Liu, Yongjun,Xu, Xiaoliang,Zhang, Yongmin
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p. 445 - 448
(2007/10/03)
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- Benzotriazole-Mediated Conversions of Aromatic and Heteroaromatic Aldehydes to Functionalized Ketones
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Aromatic and heteroaromatic aldehydes reacted with benzotriazole and triethyl orthoformate in THF to give the corresponding α-(benzotriazol-1-yl)aryl ethyl ethers 7 in good yield.The novel acyl anion precursors 7 underwent smooth lithiation at the methine group followed by trapping with alkyl halides, aldehydes, ketones, and imines to yield the expected substituted intermediates of type 9, which were hydrolyzed under mild conditions without isolation.Benzaldehyde, methyl-, chloro-, and methoxy-substituted benzaldehydes, 1-naphthalenecarboxaldehyde, 2- and 3-furaldehydes, 2- and 3-thiophenecarboxaldehydes, and 2-pyridinecarboxaldehyde were all transformed in this manner into a variety of aryl and heteroaryl ketones with alkyl (10), α-hydroxyalkyl (12 and 13), α-aminoalkyl (14) and acyl (15) substituents.
- Katritzky, Alan R.,Lang, Hengyuan,Wang, Zuoquan,Zhang, Zhongxing,Song, Huimin
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p. 7619 - 7624
(2007/10/03)
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- α-Imino and α-oximino carbocations. A comparison with α-carbonyl and α-thiocarbonyl carbocations
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The σ+ values for the groups m-CH=N-t-Bu and p-CH=N-t-Bu have been determined to be 0.16 and 0.078, respectively. The CH=N-t-Bu group is therefore cation-destabilizing relative to hydrogen when placed in the meta position of a cumyl cation. Although the p-CH=N-t-Bu group is still cation-destabilizing, the effect is reduced by a competing resonance effect when the imino group is placed in the para position. However, when attached directly to a cationic center, this imino group enhances rates relative to α-H. This is interpreted in terms of a cation-stabilizing conjugative effect. The σ+ value of the p-oximino group, p-CH=NOCH3, is -0.03 and indicates that a cation-stabilizing conjugative effect can essentially offset the inductive effect of this electron-withdrawing substituent in a cumyl cation. However, when attached directly to a developing cationic center, this oximino group greatly enhances cation formation rates relative to hydrogen. This group is even more cation-stabilizing than the methyl group. Studies on systems of type ArCH(OMs)C(NOCH3)Ph, where the oximino group can be syn or anti to the developing cationic center, indicate the existence of isomeric α-oximino cations, with the anti cations forming faster than the syn cations. Computational studies at the MP2/6-31G** level support the idea of extensive conjugative stabilization of α-oximino cations. Despite extensive mesomeric stabilization of α-oximimo cations, the primary cation +CH2CH=NOCH3 cannot be solvolytically generated since nucleophilic solvent displacement processes dominate. Stabilities of a series of cations of type +CH2X, where X is a formal electron-withdrawing group, have been evaluated by ab initia methods. Isodesmic reactions indicate a stability order of α-CHNOCH3 ~ CH=CH2 > CHNHCH3 > CHS > CHO ~ H > CN > NO2.
- Creary, Xavier,Wang, You-Xiong,Jiang, Ziqi
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p. 3044 - 3053
(2007/10/02)
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- Reductive Coupling of Benzoyl Cyanide and Carbonyl Compounds by Aqueous Ti(III) Ions. A New Convenient and Selective Access to the Less Stable Mixed Benzoins
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The reactive species formed by the Ti(III) ion reduction of benzoyl cyanide (1) adds to the C-atom of carbonyl compounds 2 under simple experimental conditions.The intermediate 1,2-diols 3 are smoothly converted, without isolation, into the less thermodynamically stable mixed benzoins 4, which are not accessible by the classical benzoin condensation.The possible mechanisms involved in the reaction are discussed.
- Clerici, Angelo,Porta, Ombretta
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p. 2889 - 2893
(2007/10/02)
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- Microbial Reduction of 1,2-Diketones to Optically Active α-Hydroxyketones
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The microorganisms that reduce benzil to optically active benzoin were screened.Xanthomonas oryzae IAM 1657 was selected as the best strain, which resulted in the formation of (R)-(-)-benzoin.This biochemical reduction was applied to other 1,2- and 1,3-diketones to find that only 1,2-diarylethanediones were reduced smoothly to afford the corresponding ketols.
- Ohta, Hiromichi,Konishi, Jin,Kato, Yasuo,Tsuchihashi, Gen-ichi
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p. 2421 - 2428
(2007/10/02)
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- ASYMMETRIC REDUCTION OF BENZIL TO BENZOIN CATALYZED BY THE ENZYME SYSTEM OF A MICROORGANISM
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Benzil was reduced by incubation with a bacterium in a nutrient medium to afford (R)-benzoin.Substituted benzils were also hydrogenated to the corresponding benzoins in a similar manner.
- Konishi, Jin,Ohta, Hiromichi,Tsuchihashi, Gen-ichi
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p. 1111 - 1112
(2007/10/02)
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- ADDITION OF GRIGNARD REAGENTS TO O-TRIMETHYLSILYLATED CYANOHYDRINS: SYNTHESIS OF ACYLOINS
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Grignard reagents have been found to react readily with O-trimethylsilylated cyanohydrins to afford, after acid hydrolysis of intermediates, good yields of acyloins.
- Krepski, Larry R.,Heilmann, Steven M.,Rasmussen, Jerald K.
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p. 4075 - 4078
(2007/10/02)
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- Reduction of Unsymmetrical Benzils Using Sodium Dithionite
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Contrary to a previous report, reduction of unsymmetrical benzils by sodium dithionite (sodium hydrosulfite) in general yields a mixture of isomeric benzoins.Whereas the reduction of aldehydes and ketones by dithionite apparently takes place by a nucleophilic addition mechanism, the reduction of benzils proceeds by an electron-transfer mechanism.The initial product of the reduction is the (Z)-α,α'-stilbenediol which is produced stereospecifically.The ultimate benzoin products, then, result from the two different modes of ketolization of the stilbenediol intermediate.
- Heilmann, Steven M.,Rasmussen, Jerald K.,Smith, Howell K.
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p. 987 - 992
(2007/10/02)
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