21300-30-1Relevant academic research and scientific papers
Lithium Amino Alkoxide-Evans Enolate Mixed Aggregates: Aldol Addition with Matched and Mismatched Stereocontrol
Jermaks, Janis,Tallmadge, Evan H.,Keresztes, Ivan,Collum, David B.
supporting information, p. 3077 - 3090 (2018/03/08)
Building on structural and mechanistic studies of lithiated enolates derived from acylated oxazolidinones (Evans enolates) and chiral lithiated amino alkoxides, we found that amino alkoxides amplify the enantioselectivity of aldol additions. The pairing of enantiomeric series affords matched and mismatched stereoselectivities. The structures of mixed tetramers showing 2:2 and 3:1 (alkoxide-rich) stoichiometries are determined spectroscopically. Rate and computational studies provide a viable mechanistic and stereochemical model based on the direct reaction of the 3:1 mixed tetramers, but they raise unanswered questions for the 2:2 mixed aggregates.
An expedient preparation of amine-free lithium enolates using immobilized amide reagents
Lazny, Ryszard,Wolosewicz, Karol
, p. 1103 - 1106 (2013/04/23)
Amine-free lithium enolates can be prepared by a simple procedure using polymer-immobilized lithium amides derived from known, easily accessible immobilized secondary amines, or from a new bidentate amine [lithium diisopropylamide (LDA) or lithium cyclohe
Solution structures of lithium enolates of cyclopentanone, cyclohexanone, acetophenones, and benzyl ketones. Triple ions and higher lithiate complexes
Kolonko, Kristopher J.,Biddle, Margaret M.,Guzei, Ilia A.,Reich, Hans J.
supporting information; experimental part, p. 11525 - 11534 (2011/02/26)
Multinuclear NMR spectroscopic studies at low temperature (-110 to -150°C) revealed that lithium p-fluorophenolate and the lithium enolates of cyclohexanone, cyclopentanone and 4-fluoroacetophenone have tetrameric structures in THF/Et2O and THF
Probing the formation of bicyclo[4.2.0]octan-1-ols
Loughlin, Wendy A.,Rowen, Catherine C.,Healy, Peter C.
, p. 5690 - 5698 (2007/10/03)
Reaction of lithium enolates of simple ketones with (±)-phenyl vinyl sulfoxide has potential for the convergent construction of complex fused ring systems containing a bicyclo[n.2.0]alkan-1-ol. The formation of sulfinylbicyclo[4.2.0]octan-1-ols 1-3 from the lithium enolate of cyclohexanone with (±)-phenyl vinyl sulfoxide or (R)-(+)-p-tolyl vinyl sulfoxide 18 was used to probe the mode of this novel cyclization reaction. Using phenyl vinyl sulfoxide, variations in the reaction lighting and solvent were investigated, in conjunction with radical trapping (TEMPO) and isotope labeling (deuterium) experiments. Cyclization to form sulfinylbicyclooctanols 1-3 is likely to proceed via an intermediate that ring closes to the bicycloalkanol anion 11 and was presently favored by the use of solvents such as THF or DME.
Novel catalytic hydrogenolysis of silyl enol ethers by the use of acidic ruthenium dihydrogen complexes
Takei, Izuru,Nishibayashi, Yoshiaki,Ishii, Youichi,Mizobe, Yasushi,Uemura, Sakae,Hidai, Masanobu
, p. 32 - 42 (2007/10/03)
Treatment of 1-trimethylsilyloxy-1-cyclohexene (1a) in the presence of a catalytic amount of the acidic dihydrogen complex [RuCl(η2-H2)(dppe)2]OTf (4a) [dppe=1,2-bis(diphenylphosphino)ethane, OTf=OSO2CF3] (10 mol.%) under 1 atm of H2 in anhydrous ClCD2CD2Cl at 50 °C for 8 h afforded cyclohexanone (3a) and Me3SiH in quantitative NMR yields. Silyl enol ethers such as 1-triethylsilyloxy-1-cyclohexene (1b), 1-t-butyldimethylsilyloxy-1-cyclohexene (1c), and other trimethylsilylethers (1d, 1e, and 1f) reacted similarly with H2 to afford the corresponding ketones and trialkylsilanes. The direct proton transfer from H2 to the trimethylsilyl enol ethers (1a and 1d-1f) was confirmed by the experiments employing D2 gas, where α-monodeuterated ketones (3a′ and 3d′-3f′) were obtained in high yields. The enantioselective protonation of prochiral silyl enol ethers with 1 atm of H2 by employing [RuCl(η2-H2) ((S)-BINAP)2]OTf (4e) [BINAP=2,2′-bis (diphenylphosphino)-1,1′-binaphthyl] and [RuCl(η2-H2)((R, R)-CHIRAPHOS)2]OTf (4f) [CHIRAPHOS=2,3-bis(diphenylphosphino)butane] showed that no enantioselectivity was observed in either catalytic or stoichiometric protonation reactions under various reaction conditions. The reaction of [RuHCl(dppe)2] (5a) with one equivalent of Me3SiOTf under 1 atm of H2 produced rapidly 4a, concurrent with the formation of Me3SiH. Based on these studies, the mechanism for this novel hydrogenolysis of silyl enol ethers is proposed which involves heterolytic cleavage of the coordinated H2 on the ruthenium atom caused by the nucleophilic attack of the oxygen atom of enol ethers to give ketones and Me3SiOTf, and the subsequent reaction of the resultant complex 5a with Me3SiOTf under 1 atm of H2 to regenerate the original dihydrogen complex 4a. On the other hand, the stoichiometric reaction of a lithium enolate 6e with one equivalent of 4e at -78 °C in CH2Cl2 under 1 atm of H2 afforded 2-methyl-1-tetralone (3e) with 75% ee (S) in >95% yield, together with the formation of [RuHCl((S)-BINAP)2] (5e).
The thiopyran route to polypropionates revisited: Selective syn and anti aldol reactions via 3,6-dihydro-4-trimethylsilyloxy-2H-thiopyran
Ward, Dale E.,Man, Chuk,Guo, Cheng
, p. 2201 - 2202 (2007/10/03)
Aldol reaction of the amine free Li enolate of tetrahydro-4H-thiopyran-4-one with 1,4-dioxa-8-thi aspiro[4.5]decane-6-carboxaldehyde gives mainly the 2,3-anti-3,4-syn aldol (7:1) in good yield; reaction of the LDA generated lithium enolate proceeds poorly. Using the trimethylsilyl enol ether and TiCl4 gives the 2,3-syn-3,4-syn aldol (>10:1). The adducts can be used for polypropionate synthesis.
On the Structure and Reactivity of Lithium Diisopropylamide (LDA) in Hydrcarbon Solutions. Formation of Unsolvated Ketone, Ester, and Carboxamide Enolates
Kim, Yong-Joo,Bernstein, Max P.,Galiano Roth, Angela S.,Romesberg, Floyd E.,Williard, Paul G.,et al.
, p. 4435 - 4439 (2007/10/02)
Enolizations of ketones, tert-butyl esters, and carboxamides by solvent-free lithium diisopropylamide (LDA) in hexane or toluene are described.Enolates are isolated as spectroscopically pure, white (often crystalline) solids.Solubilities of the enolates in hexane range from highly soluble to completely insoluble.Enolization of aldehydes, methyl esters, and acetone afford complex mixtures.Analysis of LDA and LDA in hexane by 6Li and 15N NMR spectroscopy show evidence of an equilibrium mixture of at least three cyclic oligomers.
Proton affinities and aggregation states of lithium alkoxides, phenolates, enolates, β-dicarbonyl enolates, carboxylates, and amidates in tetrahydrofuran
Arnett, Edward M.,Moe, Kevin D.
, p. 7288 - 7293 (2007/10/02)
The proton affinities of the title compounds are represented by their heats of deprotonation, ΔHdep, through reactions with lithium bis(trimethylsilyl)amide, LiHMDS, in tetrahydrofuran at 25°C. Aggregation numbers of the parent acid and of its lithium salt at a concentration of 0.10 M were obtained by vapor-pressure osmometry at 37°C. Lithium phenolates were also studied by conductivity at 25°C. ΔHdeps for 27 oxygen, nitrogen, and carbon acids of varied types correlate fairly well (R = 0.95) with their published pKas in dimethyl sulfoxide although their degrees of aggregation in THF vary from one to over seven. In some cases, the ΔHdep of an acid is strongly dependent on the concentration ratio of LiHMDS to that of the acid's lithium salt at the time of measurement. Aggregation numbers determined by VPO in this report agree with available published values obtained by previous workers using several techniques. There is no obvious relationship between the aggregation number of the lithium salt and the basicity of the corresponding anion as represented by ΔHdep. This observation along with independent evidence for equilibria between monomers, dimers, tetramers, etc. for a number of compounds indicate that there are only small differences between the relative stabilities of different aggregation states. Conductance data for lithium p-nitrophenolate were treated by Wooster analysis, the results of which suggest equilibria between ion triplets, ion pairs, and free ions in THF. The conductance of LiHMDS in this solvent is surprisingly high, and this property was used to demonstrate an interaction between LiHMDS and lithium o-tert-butylphenolate.
REACTIVITY OF CARBANIONS. XI. REACTIONS OF ALKALINE SALTS OF FLUORENE AND 9-PHENYLFLUORENE WITH CYCLOHEXANONE
Beletskaya, I. P.,Solov'yanov, A. A.,Karpyuk, A. D.,Kucheryavenko, O. P.,Reutov, O. A.
, p. 1183 - 1187 (2007/10/02)
The reaction of alkali (Li, Na, K, and Cs) and tetrabutylammonium salts of fluorene and of lithium salt of 9-phenylfluorene with cyclohexanone was studied in dimethoxyethane, ether, benzene, and hexamethylphosphorotriamide.The reaction proceeds to give both addition and enolization.The reaction is an equilibrium process as shown by a study of the reverse reactions: decomposition of the alcoholate and the reactions of the alkaline enolates of cyclohexanone with fluorene.The position of the equilibrium is very sensitive to the nature of the cation and the solvent and the carbanion structure.The possible causes for this effect are considered.
Cobalt-Mediated 1,4-Acylation/Alkylation of 1,3-Dienes
Hegedus, Louis S.,Inoue, Yoshio
, p. 4917 - 4921 (2007/10/02)
Acylcobalt complexes prepared from NaCo(CO)4 and organic halides reacted with butadiene, isoprene and allene to form (acyl-?-allyl)cobalt complexes.Reaction of these with stabilized carbanions resulted in alkylation at the unsubstituted ?-allyl terminus.The procedure provides an overall 1,4-acylation/alkylation of 1,3-dienes in which three carbon-carbon bonds are formed in a one-pot, four-step reaction sequence.
