Cesium Enolate Research Articles

Photocatalyzed Direct α-Alkylation of Esters Using Styrenes.

A mild photocatalyzed approach to achieve the α-alkylation of esters via formation of an α -radical is disclosed here. Cesium enolates of esters were generated in situ using Cs2CO3 as a base. A subsequent photocatalyzed oxidation at the α-carbon of these enolates produced an α-radical that was added into activated alkenes. This is the first example accessing the α-carbon radical of esters in photoredox catalyed transformations.

セシウムエノラートの分子内 ipso 置換を経由する5, 4'-二置換型フラボン類の効率的合成

セシウムエノラートの分子内 ipso 置換を経由する5, 4'-二置換型フラボン類の効率的合成

An Effective Synthesis of 5,4'-Disubstituted Flavones via a Cesium Enolate Assisted Intramolecular ipso-Substitution Reaction

A variety of 5,4'-disubstituted flavones, which are anticipated to be androgen receptor antagonists to treat diseases mediated by the androgen receptor, were synthesized. It was found that an intramolecular ipso-substitution reaction via cesium enolate using 2-fluoro-6-hydroxyacetophenone and various benzoyl chlorides was effective in the preparation of 5-hydroxy-4'-alkylflavones.

Perspectives on computational organic chemistry.

The author reviews how his early love for theoretical organic chemistry led to experimental research and the extended search for quantitative correlations between experiment and quantum calculations. The experimental work led to ion pair acidities of alkali-organic compounds and most recently to equilibria and reactions of lithium and cesium enolates in THF. This chemistry is now being modeled by ab initio calculations. An important consideration is the treatment of solvation in which coordination of the alkali cation with the ether solvent plays a major role.

4+2]-Annulations leading to configurationally homogeneous bicyclo[4.4.0]decanediones with five new stereocenters

Bicyclo[4.4.0]decanediones 16 and 21 were prepared in 3-step sequences and their congener 23 as well as bicyclo[4.4.0]decanetrione 24 by subsequent modification. In step 1 the cesium enolate of γ,δ-unsaturated β-ketoester 13 was annulated to the ester-substituted cyclohexenones 6 (achiral; simple diastereoselectivity observed) and 18 (chiral; simple and induced diastereoselectivity observed). In step 2, Pd-catalyzed fragmentation provided bicyclo[4.4.0]decanediones 15 and 20, respectively. De(methoxycarbonylation) of the latter in step 3 furnished compounds 16 and 21.

Aggregation and reactivity of the cesium enolate of 6-phenyl-alpha-tetralone: comparison with the lithium enolate.

The cesium enolate of 6-phenyl-alpha-tetralone (CsPAT) has a lambda(max) in THF at about 387 nm, but the variation with concentration is too small for application of singular value decomposition. Proton-transfer studies with several indicators show that CsPAT forms monomer-tetramer mixtures with a tetramerization equilibrium constant, K(1,4) = 2.3 x 10(11) M(-3). The pK of the monomer is 23.39 on a scale where fluorene is assigned 22.9 (per hydrogen). For comparison, the lithium enolate, LiPAT, is also a monomer-tetramer with K(1,4) = 4.7 x 10(10) M(-3) and a monomer pK = 14.22. HMPA in large amounts promotes dissociation to monomer with both enolates. Ion-pair S(N)2 initial rates were measured for CsPAT with several alkyl halides and with methyl tosylate and compared with other rates with LiPAT. In all cases, the enolate monomers are much more reactive than the aggregates. Reaction of CsPAT with alkyl halides is generally C-alkylation but HMPA promotes increasing amounts of O-alkylation. A new indicator, 11-methyl-11H-benzo[b]fluorene, has a pK on the cesium scale of 23.39.

Aggregation and Alkylation of Enolates of 2-Phenyl-α-tetralone and 2,6-Diphenyl-α-tetralone1

The cesium (1-Cs, CsPhPAT) and lithium (1-Li, LiPhPAT) enolates of 2,6-diphenyl-α-tetralone, 1, and the lithium enolate (2-Li, LiPhAT) of 2-phenyl-α-tetralone, 2, are present in dilute THF solution as monomers and dimers with K1,2 = 1810 (1-Cs, CsPhPAT), 2650 (1-Li, LiPhPAT), and 1930 (2-Li, LiPhAT) M-1. These values were obtained by singular value decomposition analysis of the UV spectra and by the dependence of ion pair pK's with concentration. On the ion pair pK scales previously defined, the monomers have pK = 17.80 (1-Cs, CsPhPAT) and 11.14 (1-Li, LiPhPAT). The monomers are much faster than dimers in alkylation reactions; reaction products from alkyl halides are those of C-alkylation, but 1-Cs (CsPhPAT) with methyl sulfonates gives large amounts of O-alkylation. Comparison with previous results shows that the reactivity of cesium enolates parallels their basicity but that lithium enolates show no correlation between ion pair pK and alkylation reactivity.

Aggregation and Reactivity of the Lithium Enolate of 2-Biphenylylcyclohexanone in Tetrahydrofuran1

Deprotonation of biphenylylcyclohexanone (BPCH) with a lithium base in THF occurs preferentially at the secondary enolate position to give the unconjugated lithium enolate which is gradually converted to the more stable conjugated enolate by further proton transfer from the tertiary enolate position of the ketone. The unconjugated lithium enolate is present dominantly as the tetramer, but it is the monomer that reacts with ketone to give the conjugated enolate, LiBPCH. The conjugated enolate is present as a monomer−dimer mixture with K1,2 = 4300 M-1. The equilibrium constant changes only slightly at lower temperatures, indicating that dimerization is primarily entropy-controlled. The ion pair pK of LiBPCH, 12.3, is 6.0 units less than that of the corresponding cesium enolate, CsBPCH. Alkylation of LiBPCH with methyl brosylate or benzylic bromides occurs at the tertiary carbon, and kM ≫ kD. These reactions are faster than those of LiPhIBP, although LiPhIBP has a higher ion pair pK value. The ion pair displacement reaction has a relatively low activation energy but a normal entropy of activation.

Aggregation and ion pair acidity in THF: lithium and cesium enolates of α-phenylcyclohexanone

The lithium (1) and cesium (2) enolates of α-phenylcyclohexanone, PCH, have been studied in THF at 25°C. Both form monomer-dimer equilibria with K1,2 = 2.8 × 103 M-1 for 1 and 1.8 × 103 M-1 for 2. The ultraviolet-visible (UV-vis) spectra of the monomers and dimers were derived from the spectra of the enolates at a series of concentrations by singular value decomposition. Measurements of the ion pair pK values gave pK = 12.7 for 1 and 19.8 for 2. The monomers of 1 and 2 are alkylated by benzyl halides faster than are the dimers.Key words: carbon-acid ionization, enolate ions, ion pairs, ion pair acidity, aggregation, dimerization constants, alkylation.

Aggregation and Alkylation of the Cesium Enolate of 2-p-Biphenylylcyclohexanone(1).

The cesium enolate of 2-biphenylylcyclohexanone (CsBPCH), generated by deprotonation of 2-biphenylylcyclohexanone with diphenylmethylcesium, is shown to be a mixture of monomer and dimer in THF, with a dimerization constant of 1.9 x 10(3) M(-)(1). The ion pair acidity corresponds to pK = 19.30 +/- 0.05. Even in the presence of excess dimer, only monomeric CsBPCH is found to react with methyl tosylate (MeOTs), methyl p-bromobenzenesulfonate (MeOBs), hexyl tosylate (HexOTs), hexyl bromide (HexBr) and p-tert-butylbenzyl chloride (BBCl). The relative reactivities of these alkylating reagents toward monomeric CsBPCH are BBCl, 1.00; MeOTs, 1.21; MeOBs 6.7; HexBr, 0.10; HexOTs, 0.050. CsBPh(4) has essentially no effect on the rates.

Ion Pair Acidities and Aggregation of Some Amide and Oxazoline Enolates in THF,

Equilibrium lithium ion pair acidities at 25 °C have been determined in THF for the following acetamides: N,N-dimethyl-(4-biphenylyl)acetamide (1) (19.69), N,N-diethyl-(4-biphenylyl)acetamide (2) (20.30), N,N-dimethyl-diphenylacetamide (3) (20.76), N,N-diethyl-diphenylacetamide (4) (21.99), and 1-(diphenylmethylcarbonyl)pyrrolidine (5) (21.08). These acidity data compare well with those previously reported for the corresponding cesium enolates. Lithium and cesium ion pair acidities in THF are reported for two oxazolines: 2-(4-biphenylylmethyl)oxazoline (6) (Li, 21.53; Cs, 25.49) and (E)-(4S,5R)-2-(4-biphenylylmethyl)-4-methoxymethyl-5-phenyloxazoline (7) (Li, 20.10; Cs 24.21). Studies of their acidities over a wide range of concentrations indicate that all of the lithium and cesium enolates of 1−7 are essentially monomeric at concentrations ranging from 10-3 to 10-4 M. Traces of dimer were detected for the lithium enolates of amides 1 and 2 and for the cesium enolate of oxazoline 6. Their dimerization constants (M-1) were found to be about 450, 200, and 150, respectively. All of the other lithium and cesium enolate probably form small amounts of dimer, but the dimerization constant of <100 M-1 is below the limit of precision of our spectroscopic method.

Aggregation and ion pair acidity in THF: lithium and cesium enolates of α-phenylcyclohexanone

Aggregation and ion pair acidity in THF: lithium and cesium enolates of α-phenylcyclohexanone

Aggregation and Reactivity of the Cesium Enolate of p-Phenylisobutyrophenone in Tetrahydrofuran1

Reinvestigation of the cesium enolate (CsPhIBP) of 1-biphenylyl-2-methylpropanone (p-phenylisobutyrophenone, PhIBP) in tetrahydrofuran (THF) solution at 25.0 °C shows that its UV−visible spectrum changes with concentration with λmax moving to longer wavelengths in more dilute solution. Analysis of the spectral data over a wide concentration range by singular value determination (SVD) combined with the pK measurements indicates a mixture of monomer (M), dimer (D), and tetramer (T) with equilibrium constants of K1,2 = D/M2 = 2.89 × 104 M-1 and K1,4 = T/M4 = 7.78 × 1012 M-3. The pK of the monomer is 25.08. The data are also compared with the corresponding data obtained for the lithium ion pair system reported in the following paper. We find that the cesium ion pair is more highly aggregated and much more basic than the lithium ion pair. The average aggregation number of CsPhIBP at 10-3 M is 3.2, substantially greater than the value of 2.2 reported previously; the revision arises from our taking into account ...

Cesium Ion Pair Acidities of some N,N-Dialkylacetamides and Aggregation of Their Cesium Enolates in Tetrahydrofuran.

Cesium ion pair acidities are reported of some N,N-dialkylacetamides at 25 degrees C in tetrahydrofuran. The cesium enolates of alpha-arylacetamides are essentially monomeric at concentrations of about 10(-)(4) M, but small amounts of dimers are present for the enolates of N,N-dimethyl- and N,N-diethyl(4-biphenylyl)acetamide (K(dimer) is approximately 400 M(-)(1)). The cesium enolate of N,N-dimethyldiphenylacetamide forms small amounts of dimers, but the dimerization constant of <100 M(-)(1) is near the limit of detection of our methods. The enolate of N,N-diethylacetamide has an average aggregation number of 3.3, consistent with a mixture of dimers and tetramers. The cesium ion pair pKs of the alpha-arylacetamides are about 25-26, and that of N,N-diethylacetamide is greater than 33.7. The acidity data are in good agreement with measurements that have been reported in the literature for similar systems.

Lithium and Cesium Ion-Pair Acidities of Dibenzyl Ketone. Aggregation of Lithium and Cesium Ion Pairs of the Enolate Ion and Dianion1,

Spectral study of the cesium and lithium enolates of dibenzyl ketone (DBK) showed that both salts exist as contact ion pairs in THF solutions. The spectral data for the dicesium salt of DBK indicate that it exists as triple ions in which both cations are in contact with the dianion. The dilithium salt of DBK forms triple ions of two types in THF: in one, both cations are in contact with the DBK dianion, in the other, one of the lithium cations is solvent-separated. Evidence for dimerization of the ion pairs was obtained for both lithium and cesium enolates of DBK from UV-vis spectral (blue shift of the absorbance band at higher concentrations) and acidity (the decrease of pK at higher concentrations) studies. The dimerization constant for the cesium enolate of DBK obtained from the acidity data (3.5 x 10(3) M(-)(1)) is considered to be more accurate than that from the spectral analysis (1.7 x 10(3) M(-)(1)). The lithium enolate is much less dimerized than its cesium counterpart with a dimerization constant from acidity data of 4.2 x 10(2) M(-)(1). The first and second cesium pK values of DBK are 18.07 and 33.70, respectively, compared to the first lithium pK of 11.62.

Counterion effects in the anionic polymerization of methyl methacrylate: Mechanistic relevance to GTP

AbstractThe room temperature polymerization of methyl methacrylate (MMA) by the cesium or tetrabutylammonium salt of 9‐methylfluorenide proceeds in an uncontrolled fashion. To understand these results, we have studied the structure of the propagating chain‐ends using polymer microstructure and stopped‐flow FT‐IR spectroscopy of model compounds. Deprotonation of methyl isobutyrate with the cesium salt of 1,1,4,4‐tetraphenylbutane dianion afforded the corresponding cesium enolate (U=1645 cm−1). The deprotonation of methyl 2,2,4‐trimethyl‐4,6‐dicarbomethoxyhept‐6‐en‐1‐oate (the trimeric ester of MMA) was accompanied by a rapid (2–4 s) intramolecular cyclization. Comparison of group transfer polymerization (GTP) to anionic polymerization reveals that the counterion is important but probably not the sole mechanistic feature responsible for the living behavior of GTP.

Carbon acidity. 84. Kinetics of methylation of a cesium enolate in THF. The importance of the free enolate ion in an aggregated system

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCarbon acidity. 84. Kinetics of methylation of a cesium enolate in THF. The importance of the free enolate ion in an aggregated systemJames A. Krom and Andrew StreitwieserCite this: J. Am. Chem. Soc. 1992, 114, 22, 8747–8748Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://doi.org/10.1021/ja00048a084RIGHTS & PERMISSIONSArticle Views113Altmetric-Citations17LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (332 KB) Get e-Alerts Get e-Alerts