Organocatalytic Enantioselective Protonation of Silyl Enolates Mediated by Cinchona Alkaloids and a Latent Source of HF

Poisson, Thomas; Dalla, Vincent; Marsais, Francis; Dupas, Georges; Oudeyer, Sylvain; Levacher, Vincent

doi:10.1002/anie.200701683

Cited by 84 publications

(36 citation statements)

References 34 publications

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“…Elemental analyses performed at the Organic Chemistry Department of Eötvös Loránd University (Budapest, Hungary) were undertaken on IIa, IVc, V, and VIII and were within 0.4% of the calculated values. The remaining compounds have been described previously (I-IV: [12,17,18]; VI: [19], VII: [15]) and had melting points in accord with the literature values. The structures of the investigated compounds and their numbering used are shown in Fig.…”

Section: Chemistrymentioning

confidence: 75%

Structural studies of seven homoisoflavonoids, six thiohomoisoflavonoids, and four structurally related compounds

et al. 2011

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1 H and 13 C NMR chemical shifts have been determined and assigned based on PFG 1 H, 13 C HMQC, and HMBC experiments for 3-(4 0 -X-benzyl)-4-chromenones (Ia, X = CN and Ib, X = NO 2 ), 3-(4 0 -X-benzyl)-4-thiochromenones (IIa, X = Cl and IIb, X = Br), (E)-3-(4 0 -Xbenzylidene)-4-chromanones (IIIa-IIIe, X = OCH 3 , CH 3 , Cl, N(CH 3 ) 2 , Br), (Z)-3-(4 0 -X-benzylidene)4-thiochromanones (IVa-IVd, X = Cl, Br, F, OCH 3 ), 2-benzyl-1,2,3, 4-tetrahydro-1-naphthol (V), 2-benzyl-and (E)-2-benzylidene-1-tetralones (VI and VII), and (E)-2-benzylidene-1-benzosuberol (VIII). The crystal structures have been determined for the following seven compounds: derivatives of 4-chromanones (IIIa-IIId), 1-tetrahydronaphtol (V), and 1-tetralones (VI and VII). The molecular features and intermolecular interactions in crystal state have been discussed.

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Section: Chemistrymentioning

confidence: 75%

Structural studies of seven homoisoflavonoids, six thiohomoisoflavonoids, and four structurally related compounds

et al. 2011

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“…Whereas asymmetric protonation of silyl enolates catalysed by organometallic species has reached high levels of efficiency in terms both of enantioselectivity and of substrate scope, the first organocatalytic version was only described, by Levacher et al, in 2007 6a. Several years later, the same group provided a full report of their work, illustrating the usefulness of their organocatalytic approach in the synthesis of natural products 18.…”

Section: Catalytic Asymmetric Protonation Of Enol Derivativesmentioning

confidence: 99%

Redox Non‐Innocence of Coordinated 2‐(Arylazo) Pyridines in Iridium Complexes: Characterization of Redox Series and an Insight into Voltage‐Induced Current Characteristics

Goswami

Sengupta

Paul

et al. 2014

Chemistry A European J

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Two examples of a rare class of di-radical azo-anion complexes of 2-(arylazo) pyridine with Ir(III) carrier are introduced. Their electronic structures have been elucidated using a host of physical methods that include X-ray crystallography, cyclic voltammetry, electron paramagnetic resonance spectroscopy, and density functional theory. Room temperature magnetic moments of these are consistent with two nearly non-interacting azo-anion radicals. These displayed rich electrochemical properties consisting of six numbers of reversible and successive one electron CV-waves. Redox processes occur entirely at the coordinated ligands without affecting metal redox state. Apart from reporting their chemical characterization, I-V characteristics of these complexes in film state are investigated using sandwich-type devices comprising of a thin film of 100-125 nm thickness placed between two gold-plated ITO electrodes. These showed memory switching properties covering a useful voltage range with a reasonable ON/OFF ratio and also are suitable for RAM/ROM applications. I-V characteristics of two similar complexes of Rh and Cr with identical ligand environment and electronic structure are also referred for developing an insight into the memory switching ability of Ir- and Rh- complexes on the basis of comparative analysis of responses of the respective systems. In a nutshell, thorough analysis of voltage driven redox dynamics and corresponding solid and solution state current responses of all the systems are attempted and there from an unexplored class of switching devices are systematically introduced.

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“…Preparation of 2-Fluoro-1-tetralone 3f:To a solution of 2-(ethoxycarbonyl)tetralone 13 (1.107 g, 5 mmol) in MeCN (40 mL) was added TiCl 4 (0.15 mL, 0.75 mmol) at r.t. After 5 min SelectfluorTM (2.157 g, 6.1 mmol) was added and the resulting mixture was stirred at r.t for an additional 3 h. The reaction was carefully quenched with NaHCO 3 (50 mL) and extracted with Et 2 O (4 × 40 mL). The combined organic layers were washed with brine (50 mL), dried over MgSO 4 and concentrated.…”

mentioning

confidence: 99%

“…c Determined by HPLC. The absolute configuration of 3a-e and 3g,h were assigned by comparison with literature data 3. The absolute configuration of 3i was assigned by comparison with literature data.12 …”

mentioning

confidence: 99%

Straightforward Organocatalytic Enantioselective Protonation of Silyl Enolates by Means of Cinchona Alkaloids and Carboxylic Acids

Poisson¹,

Oudeyer²,

Dalla³

et al. 2008

Synlett

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The combination of cinchona alkaloids and carboxylic acids provides a very simple chiral proton source. By using this system, enantioselective protonation of silyl enolates was achieved affording the corresponding ketones in high yields and in up to 75% ee.The enantioselective protonation of prochiral enol derivatives has emerged as a helpful tool to achieve optically enriched carbonyl compounds possessing a tertiary stereogenic carbon center at the a-position. 1 The successful development of various catalytic deracemization processes over the last fifteen years made this approach more synthetically useful and quite complementary to the catalytic enantioselective alkylation technology, generating nowadays increasing interest amongst the synthetic chemistry community. 2 We have recently reported the first organocatalytic enantioselective protonation of silyl enolates 2 by means of cinchona alkaloids and a 'latent source of HF'. 3 This organocatalytic approach offers unprecedented mild, neutral and metal-free conditions with excellent yields and high enantioselectivities of up to 92% (Figure 1a). 3 Mechanistically, the strategy relies on the in situ catalytic generation of a hydrogen fluoride salt 1-HF through the reaction between an acid fluoride and an alcohol in the presence of a chiral tertiary amine 1. As a result of the high silicon-fluoride affinity, the active catalytic species 1-HF can exert a specific silyl enolate activation mode (Figure 1c; X = F -) to promote the protonation of silyl enolate 2 along with the regeneration of the precatalyst 1.Within our continuing interest to develop a more straightforward and general approach for the organocatalytic enantioselective protonation of silyl enol ethers, we queried whether our methodology could be rendered more atom economic and operationally simpler by replacing the two-component, naked source of HF with a more readily handy proton source such as a simple carboxylic acid (Figure 1b).According to this new scenario, the protonation of a tertiary amine 1 by a carboxylic acid would generate the corresponding hydrogen carboxylate salt 1-RCO 2 H. This species should be a better protonating agent than the rather more acidic carboxylic acid itself, due to the cooperative activation of the silyl enolate 2 by the carboxylate counterion ( Figure 1c; X = RCO 2 -) through generation of either an enolate or a hypervalent silicate. 4 Considering this cooperative activation mode as a prerequisite for achieving high levels of stereoinduction, 3 the question then arose whether the carboxylate counter-anion would be capable to enhance the silyl enol ether nucleophilicity with similar efficiency as the fluoride ion did in our previous approach. Actually, the capacity of carboxylate anions to serve such an effective Lewis base catalyst has recently been proven by reports from the Fu 5 and Mukaiyama 6 groups dealing with the C-acylation of silyl ketene acetals and the catalytic Mannich-type reaction between trimethylsilyl enol ethers and aldimines, respectively.

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Organocatalytic Enantioselective Protonation of Silyl Enolates Mediated by Cinchona Alkaloids and a Latent Source of HF

Cited by 84 publications

References 34 publications

Structural studies of seven homoisoflavonoids, six thiohomoisoflavonoids, and four structurally related compounds

Structural studies of seven homoisoflavonoids, six thiohomoisoflavonoids, and four structurally related compounds

Redox Non‐Innocence of Coordinated 2‐(Arylazo) Pyridines in Iridium Complexes: Characterization of Redox Series and an Insight into Voltage‐Induced Current Characteristics

Straightforward Organocatalytic Enantioselective Protonation of Silyl Enolates by Means of Cinchona Alkaloids and Carboxylic Acids

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