- Tautomerism in bis(oxazoline)s
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Bis(oxazoline)s (BOXs) are a privileged ligand class and have found widespread use in catalysis. Herein, the tautomerism of selected BOX ligands was evidenced by X-ray diffractometry as well as by NMR and IR spectroscopy and supported by DFT calculations. In CDCl3 solution at room temperature, the new 1,1-bis(4,4-dimethyl-1,3-oxazolin-2-yl)-1-phenylmethane ( Ph,HBOX-Me2) ligand is present as a 1:1 mixture of the diimine and iminoenamine tautomers. Thermodynamic and kinetic data for the tautomeric equilibrium were determined, which allowed comparison with related bidentate ligand classes. The other BOXs studied, H,HBOX-Me 2, Me,HBOX-Me2, and tBu,HBOX-Me 2, are largely present in the diimine form under similar conditions. IR spectroscopy was identified as a valuable tool for detecting the presence of the iminoenamine form as a minor component. Tautomerism in the prominent bis(oxazoline) ligand class is evidenced by X-ray diffractometry as well as by NMR and IR spectroscopy and supported by DFT calculations. Thermodynamic and kinetic data for the tautomeric equilibrium are determined for a specific example, which allows comparison with related bidentate ligand classes. Copyright
- Walli, Adam,Dechert, Sebastian,Meyer, Franc
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- Enantioselective Desymmetrization of 2-Aryl-1,3-propanediols by Direct O-Alkylation with a Rationally Designed Chiral Hemiboronic Acid Catalyst That Mitigates Substrate Conformational Poisoning
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Enantioselective desymmetrization by direct monofunctionalization of prochiral diols is a powerful strategy to prepare valuable synthetic intermediates in high optical purity. Boron acids can activate diols toward nucleophilic additions; however, the design of stable chiral catalysts remains a challenge and highlights the need to identify new chemotypes for this purpose. Herein, the discovery and optimization of a bench-stable chiral 9-hydroxy-9,10-boroxarophenanthrene catalyst is described and applied in the highly enantioselective desymmetrization of 2-aryl-1,3-diols using benzylic electrophiles under operationally simple, ambient conditions. Nucleophilic activation and discrimination of the enantiotopic hydroxy groups on the diol substrate occurs via a defined chairlike six-membered anionic complex with the hemiboronic heterocycle. The optimal binaphthyl-based catalyst 1g features a large aryloxytrityl group to effectively shield one of the two prochiral hydroxy groups on the diol complex, whereas a strategically placed "methyl blocker"on the boroxarophenanthrene unit mitigates the deleterious effect of a competing conformation of the complexed diol that compromised the overall efficiency of the desymmetrization process. This methodology affords monoalkylated products in enantiomeric ratios equal or over 95:5 for a wide range of 1,3-propanediols with various 2-aryl/heteroaryl groups.
- Estrada, Carl D.,Ang, Hwee Ting,Vetter, Kim-Marie,Ponich, Ashley A.,Hall, Dennis G.
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supporting information
(2021/04/07)
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- A amide alkaloid fully synthetic method
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The invention discloses a total synthesis method of amides alkaloid, and belongs to the technical field of the chemistry of natural products. The total synthesis method comprises the following steps: carrying out the synthesis by adopting malonate and 2-bromopropane or 2-bromopropane derivative as raw materials, thereby obtaining isopropyl malonate; (2) carrying out the synthesis by adopting 2-aminopyrrolidine as a raw material, thereby obtaining mid-body 2-amino tetralin pyrrolidine; and (3) synthesizing amides alkaloid 3-isopropyl-nafoxidine[1,2-alpha]pyrimidine-2,4(1H,3H)-diketone and a derivative by adopting the isopropyl malonate and the 2-2-amino tetralin pyrrolidine as a raw material. By adopting the total synthesis method, the defect that the extraction separation process in the natural product is complicated and the yield is low can be overcome, and the demand of perople for further researching the natural product can be satisfied; moreover, the synthesis method is simple in route, raw materials are cheap and easy to obtain, and the yield is relatively high.
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Paragraph 0056; 0057
(2017/08/25)
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- Synthesis and acidity of conformationally constrained 1,3-oxathiane S-oxides
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Conformationally constrained 5-tert-butyl 1,3-oxathiane was synthesized and oxidation led to the diastereoisomeric sulfoxides and the respective sulfone. Stereoelectronic effects are discussed for these compounds and their corresponding 2-carbanions. pKavalues are calculated for these compounds and compared with the respective 1,3-dithiane-derived sulfide, the sulfoxides, and the sulfone.
- Weingand, Daniel,Podlech, Joachim
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supporting information
p. 5608 - 5610
(2016/11/28)
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- METHOD OF PRODUCING 3-ETHOXY-2-TERT-BUTYL ALKYL PROPIONATE
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PROBLEM TO BE SOLVED: To provide a novel production method of 3-ethoxy-2-tert-butyl alkyl propionate used for the production of an olefin polymerization solid catalyst. SOLUTION: A 2-ethoxy methyl malonic acid diester derivative represented by formula (1) (where R1 and R2 represent a 1-4C alkyl group) is reacted in the presence of a base. COPYRIGHT: (C)2015,JPO&INPIT
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Paragraph 0039; 0040
(2016/12/22)
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- Selective sulfenylative desulfonylation or decarbalkoxylation of α-sulfonyl malonates with DABCO or Bu3N: Reactivity and conformational analysis
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The study on reactivity of severalαsubstituted αsulfonyl malonates toward 1,4-diazabicyclo[2.2.2]octane (DABCO) and Bu3N is described. The reactivity with DABCO revealed the possible competition between decarbalkoxylation and unexpected desulfonylation, depending on the-substituent, because of sterical hindrance around the electrophilic centers (SO2 and CO2R). The derivatives with crowded α-substituents suffer selective desulfonylation, and a novel and efficient desulfonylation method can be proposed. The dependence of the reactivity ofα-sulfonyl malonates on the sterical hindrance around the electrophilic centers is confirmed by conformational analysis (Macromodel/MM2* and Mopac/MP3). The carbanionic mechanism is proved because the corresponding protonated, deuterated, and sulfenylated products were obtained by addition of the corresponding electrophilic agents. Bu3N showed itself to be a novel selective decarbalkoxylation agent for any-substituted-sulfonyl malonate.
- Donnici, Claudio L.,Pereira, Elaine Henriques Teixeira,Lopes, Julio C. Dias,Marzorati, Liliana,Wladislaw, Blanka
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scheme or table
p. 342 - 350
(2010/04/04)
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- ORGANOMANGANESE (II) REAGENTS XV. CONJUGATE ADDITION OF ORGANOMANGANESE REAGENTS TO ALKYLIDENEMALONIC ESTERS AND RELATED COMPOUNDS
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Organomanganese reagents react with alkylidenemalonic esters or related compounds to give the conjugate addition products in good yields.Several examples illustrate the scope and the efficiency of this reaction.
- Cahiez, Gerard,Alami, Mouad
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p. 4163 - 4176
(2007/10/02)
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- ANALYSE STRUCTURALE EN SERIE CYCLOBUTANIQUE. Partie 1. Derives monosubstitues et gem disubstitues du cyclobutane
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Methylene bending mode analysis of some cyclobutane-d2 molecules reveals that in the dissolved state (solvent CCl4), bromocyclobutane occurs exclusively in a pseudo-equatorial form, whereas, under the same conditions, cyclobutanol and 1-bromocyclobutane carbonitrile exist both in pseudo-axial and pseudo-equatorial conformations.NMR spectroscopy confirms the results obtained for bromocyclobutane and leads to the conclusion that the pseudo-equatorial conformer is predominant in the case of cyclobutanol as well as in that of cyclobutane carbonitrile.A theoretical study of cyclobutanol in the gaseous state by the P.C.I.L.O. method gives results which are consistent with a pseudo-equatorial conformer.
- Karimine, Mohamed,Galsomias, Jacqueline,Lere-Porte, Jean-Pierre,Petrissans, Jean
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p. 321 - 332
(2007/10/02)
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- Chemistry of Cumulenes, 6. Syntheses and Reactions of 1-H-Allene-1,3-dicarboxylic Acid Monoesters
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The title compounds 5a-e have been prepared.The carboxylation of allene monoesters 4 was successful with the phenyl derivative 4a only.The resulting extremely unstable halfester 5a as its benzylammonium salt was spontaneously transformed into the enamine ester 7.The alkyl-substituted allenes 5b-e are accessible via Wittig reaction of alkylmalonic monoester chlorides 11 with (alkoxycarbonyl)methylene ylides 12, which comprise the 2,2,2-trichloroethyl or the tert-butyl residues as selectively cleavable carboxylic protecting groups.Cleavage of the CCl3CH2 group with Zn succeeded for the tert-butylallenes 13a/b only.In the case of the methylallene 13c the cleavage was accompanied by hydrogenation of the allene.The mechanism of this reaction is discussed.Cleavage of the tert-butyl ester group in 13d and e was readily achieved with ether/sulfuric acid.
- Nader, Franz W.,Brecht, Angelika,Kreisz, Siegfried
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p. 1196 - 1207
(2007/10/02)
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- Synthesis of 4-Ylidenebutenolides. A Practical Route to 2-En-4-ynoic Acid Intermediates based on Conjugate Addition of Alkynyl-lithium Reagents
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Conjugate addition of alkynyl-lithium reagents to diethyl ethoxymethylenemalonate, followed by simultaneous saponification and 1,2-elimination of ethanol from the intermediate adducts, viz (18), in the presence of ethanolic potassium hydroxide, provides a useful synthesis of substituted propargylidenemalonic acids (19).Cyclisation of the propargylidenemalonic acids, using known procedures then leads to the corresponding 4-ylidenebutenolides, e.g. (20) and (21)
- Clemo, Nicholas G.,Pattenden, Gerald
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p. 2133 - 2136
(2007/10/02)
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- Ketene. Part 21. Reactions of Heterocumulenes with Nitrones
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Degradative and mass spectrometric evidence confirms the formation of the isoxazolidinones (2) from the reaction of cyano-t-butylketene with the N-alkyl nitrones (1), whilst the reaction with the N-phenyl nitrone (1d) gives the expected oxazolidinone (3b).Cyano-t-butylketene reacts with diphenyl nitrone to give the indolones (10a) and (10b).The reaction of phenyl isocyanate with diphenyl nitrone, and the N-alkyl nitrones (1a) and (1d) gives the normal 1,3-dipolar cycloadducts without rearrangement.Ethoxycarbonyl-t-butylketene reacts with the N-phenyl nitrone (1d) to give an oxazolidinone , but reaction with the N-alkyl nitrones (1) gives only fluorenone azine.This ketene reacts with diphenyl nitrone to give the anil (15) and the dihydroindole (16).
- Evans, Andrew R.,Hafiz, Mushtaq,Taylor, Giles A.
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p. 1241 - 1246
(2007/10/02)
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- Synthesis and Properties of Some tert-Alkylmalonic Acid Derivatives
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1,4-Addition of Grignard reagents to the alkylidenemalonic acid derivatives 1-8 affords the tert-alkyl malonic derivatives 9-18.The esters 9-17 give the acids 19-26 and from these the corresponding chlorides 27-34 are obtained.Bromination yields the bromo acids 35-36, the brominated acyl bromide 43, the bromonitrile 44, and the bromoacyl chlorides 37-42.The trimethylsilyl esters 50-52, the bis(2-bromoethyl) esters 53-54, the ethyl ester 14, and the tert-butyl ester 16 are brominated via the corresponding ester enolates giving the bromo esters 45-46 in pure form. - The dealkylation of malonic esters with chlorotrimethylsilane/sodium iodide has been carried out.
- Holmberg, Carl
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p. 748 - 760
(2007/10/02)
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- The Reactions of Lignin with Alkaline Hydrogen Peroxide. Part IV. Products from the Oxidation of Quinone Model Compounds
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Simple para- and orhto-quinoid structures related to lignin have been oxidized with hydrogen peroxide under mild alkaline conditions.Most of the reaction products, i.e. carboxylic acids formed by oxidative cleavage of the quinoid ring together with acids formed by more extensive degradation of the starting materials, were identified after conversion into esters.In addition, small amounts of hydroxylated quinones were found.Mechanisms for the formation of these products are suggested and the significance of the results for the bleaching of mechanical pulps with hydrogen peroxide is briefly discussed.
- Gellerstedt, Goeran,Hardell, Hanne-Lise,Lindfors, Eva-Lisa
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p. 669 - 674
(2007/10/02)
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- The Reactivity of Carbenes from Photolysis of Diazo-Compounds towards Carbon-Hydrogen Bonds. Effects of Structure, Temperature, and Matrix on the Insertion Selectivity
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Direct and/or sensitized photolyses of diazo-acetate (1a) and -malonate (1b) in hydrocarbons and ether were investigated at various temperatures in order to learn more about the nature of the C-H insertion process and the structural factors governing positional selectivity within the matrix.Photolysis of the diazo-compounds in a rigid matrix resulted in a marked decrease in the insertion selectivity, which may be interpreted as indicating that the matrix imposes severe steric demand especially on the direct C-H insertion process of the singlet carbene.The addition of a sensitizer in matrix photolysis causes a marked increase in the selectivity in the case of (1a), as is observed in the comparable liquid-phase experiment, but it causes a decrease in the case of (1b).This is interpreted as suggesting that the excited triplet (1b) itself is involved in C-H insertion under these conditions.More extensive temperature studies show that, as the temperature decreases, the C-H insertion selectivity of :CHCO2R decreases regularly regardless of the reaction phase, whereas that of :C(CO2R)2 increases in the liquid phase but decreases in the solid phase.This difference in the temperature dependence is explained by assuming that the singlet carbene is responsible for the C-H insertion of :CHCO2R throughout the temperature range studied, while both singlet and triplet are involved in the insertion of :C(CO2R)2.
- Tomioka, Hideo,Itoh, Masami,Yamakawa, Shyoji,Izawa, Yasuji
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p. 603 - 609
(2007/10/02)
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