- Enantioselective oxidation of thioanisole to metyl phenyl sulfoxide by chiral compounds bearing N-Cl bond
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Chiral sulfoxides are used in asymmetric synthesis and are present in various biologically active compounds. Asymmetric synthesis of the sulfoxides has been performed by chiral metal complexes and non-metals containing peroxide and oxide moieties. In this study, a new metal free method has been developed to oxidize thioanisole into methyl phenyl sulfoxide with easily accessible chiral compounds carrying N-Cl bond. For this purpose, chiral amine and amide bearing reagents were synthesized and chlorinated by using N-chlorosuccinimide. In oxidation reactions, chiral information has been transferred from N-chloramines to sulfides. With chlorinated chiral reagents, we observed enantioenriched sulfoxide formation. Although the observed results are promising, the best chiral amines are yet to be found. This is the first report on such a reaction, to the best of our knowledge.
- Ipek, Halil,Akdag, Akin
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- Synthesis of syn-and enantioenriched anti-β-amino alcohols by highly diastereoselective borono-Mannich allylation reactions
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A highly diastereoselective method for the synthesis of syn-β-amino alcohols and enantioenriched anti-β-amino alcohols has been developed involving α-hydroxyl aldehydes and chiral α-phenylaminoxyaldehydes or α-benzoyloxyaldehydes, respectively in Petasis borono-Mannich allylation reactions. This study broadens the scope and utility of the Petasis reaction to include pinacol allylboronate and highlights its unique reactivity and stereochemical outcomes.
- Chevis, Philip J.,Limtharakul, Thunwadee,Promchai, Thanika,Pyne, Stephen G.,Richardson, Christopher
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supporting information
p. 2220 - 2223
(2022/02/17)
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- Basicities and Nucleophilicities of Pyrrolidines and Imidazolidinones Used as Organocatalysts
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The Br?nsted basicities pKaH (i.e., pKa of the conjugate acids) of 32 pyrrolidines and imidazolidinones, commonly used in organocatalytic reactions, have been determined photometrically in acetonitrile solution using CH acids as indicators. Most investigated pyrrolidines have basicities in the range 16 aH aH aH 12.6) and the 2-imidazoliummethyl-substituted pyrrolidine A21 (pKaH 11.1) are outside the typical range for pyrrolidines with basicities comparable to those of imidazolidinones. Kinetics of the reactions of these 32 organocatalysts with benzhydrylium ions (Ar2CH+) and structurally related quinone methides, common reference electrophiles for quantifying nucleophilic reactivities, have been measured photometrically. Most reactions followed second-order kinetics, first order in amine and first order in electrophile. More complex kinetics were observed for the reactions of imidazolidinones and several pyrrolidines carrying bulky 2-substituents, due to reversibility of the initial attack of the amines at the electrophiles followed by rate-determining deprotonation of the intermediate ammonium ions. In the presence of 2,4,6-collidine or 2,6-di-tert-butyl-4-methyl-pyridine, the deprotonation of the initial adducts became faster, which allowed the rate of the attack of the amines at the electrophiles to be determined. The resulting second-order rate constants k2 followed the correlation log?k2(20 °C) = sN(N + E), where electrophiles are characterized by one parameter (E) and nucleophiles are characterized by the two solvent-dependent parameters N and sN. In this way, the organocatalysts A1-A32 were integrated in our comprehensive nucleophilicity scale, which compares n-, -, and σ-nucleophiles. The nucleophilic reactivities of the title compounds correlate only poorly with their Br?nsted basicities.
- An, Feng,Maji, Biplab,Min, Elizabeth,Ofial, Armin R.,Mayr, Herbert
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supporting information
p. 1526 - 1547
(2020/02/04)
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- Spin-Center Shift-Enabled Direct Enantioselective α-Benzylation of Aldehydes with Alcohols
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Nature routinely engages alcohols as leaving groups, as DNA biosynthesis relies on the removal of water from ribonucleoside diphosphates by a radical-mediated "spin-center shift" (SCS) mechanism. Alcohols, however, remain underused as alkylating agents in synthetic chemistry due to their low reactivity in two-electron pathways. We report herein an enantioselective α-benzylation of aldehydes using alcohols as alkylating agents based on the mechanistic principle of spin-center shift. This strategy harnesses the dual activation modes of photoredox and organocatalysis, engaging the alcohol by SCS and capturing the resulting benzylic radical with a catalytically generated enamine. Mechanistic studies provide evidence for SCS as a key elementary step, identify the origins of competing reactions, and enable improvements in chemoselectivity by rational photocatalyst design.
- Nacsa, Eric D.,MacMillan, David W. C.
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supporting information
p. 3322 - 3330
(2018/03/13)
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- The asymmetric reduction of imidazolinones with trichlorosilane
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It is shown how imidazolinones are reduced by trichlorosilane in a highly enantioselective fashion when treated with a novel Lewis base organocatalyst that is based on a 2,2′-bispyrrolidine core. Under mild reaction conditions and with low catalyst loading the hydrosilylation reaction provides a broad range of chiral imidazolidinones with various structural motifs including sterically demanding substituents, alkyls and aryls.
- Wagner, Christian,Kotthaus, Andreas F.,Kirsch, Stefan F.
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p. 4513 - 4516
(2017/04/26)
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- Aromatic Interactions in Organocatalyst Design: Augmenting Selectivity Reversal in Iminium Ion Activation
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Substituting N-methylpyrrole for N-methyindole in secondary-amine-catalysed Friedel-Crafts reactions leads to a curious erosion of enantioselectivity. In extreme cases, this substrate dependence can lead to an inversion in the sense of enantioinduction. Indeed, these closely similar transformations require two structurally distinct catalysts to obtain comparable selectivities. Herein a focussed molecular editing study is disclosed to illuminate the structural features responsible for this disparity, and thus identify lead catalyst structures to further exploit this selectivity reversal. Key to effective catalyst re-engineering was delineating the non-covalent interactions that manifest themselves in conformation. Herein we disclose preliminary validation that intermolecular aromatic (CH-π and cation-π) interactions between the incipient iminium cation and the indole ring system is key to rationalising selectivity reversal. This is absent in the N-methylpyrrole alkylation, thus forming the basis of two competing enantio-induction pathways. A simple L-valine catalyst has been developed that significantly augments this interaction.
- Holland, Mareike C.,Metternich, Jan Benedikt,Daniliuc, Constantin,Schweizer, W. Bernd,Gilmour, Ryan
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p. 10031 - 10038
(2015/07/07)
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- Improving catalyst activity in secondary amine catalysed transformations
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The effect on catalyst performance of altering substituents at the 2-position of the Macmillan imidazolidinone has been examined. Condensation of l-phenylalanine N-methyl amide with acetophenone derivatives results in a series of imidazolidinones whose sa
- Brazier, John B.,Gibbs, Timothy J. K.,Rowley, Julian H.,Samulis, Leopold,Yau, Sze Chak,Kennedy, Alan R.,Platts, James A.,Tomkinson, Nicholas C. O.
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p. 133 - 141
(2015/02/05)
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- Transfer of 1-alkenyl groups between secondary amines. Relative stability and reactivity of enamines from popular organocatalysts
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Enamines from 3-methylbutanal and several Pro- and Phe-derived secondary amines were prepared in DMSO-d6, CD3CN, and CDCl 3. For the first time, the relative thermodynamic stabilities of these and other enamines were compared, and rapid exchanges of 1-alkenyl groups were demonstrated. Competition experiments showed that the most favored enamines (without significant steric inhibition of resonance) react more rapidly with electrophiles.
- Carneros, Hector,Sanchez, Dani,Vilarrasa, Jaume
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p. 2900 - 2903
(2014/06/23)
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- Preparation and structures of 2-substituted 5-benzyl-3-methylimidazolidin- 4-one-derived iminium salts, reactive intermediates in organocatalytic transformations involving α,β-unsaturated aldehydes
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Preparations of the title compounds, 5-7 (Scheme 1 and Table 1), of their ammonium salts, 9-11 (Scheme 2 and Table 2), and of the corresponding cinnamaldehyde-derived iminium salts 12-14 (Scheme 3 and Table 3) are reported. The X-ray crystal structures of 15 cinnamyliminium PF6 salts have been determined (Table 4). Selected 1H-NMR data (Table 5) of the ammonium and iminium salts are discussed, and structures in solution are compared with those in the solid state. Copyright
- Gro?elj, Uro?,Beck, Albert,Schweizer, W. Bernd,Seebach, Dieter
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p. 751 - 796
(2014/07/07)
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- Highly enantioselective access to cannabinoid-type tricyles by organocatalytic Diels-Alder reactions
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After prosperous domino reactions towards benzopyrans, the products were used as the starting material in Lewis acid catalyzed and organocatalytic Diels-Alder reactions to build up a tricyclic system. Herein, an asymmetric induction up to 96% enantiomeric excess was obtained by the use of imidazolidinone catalysts. This approach can be utilized to construct the tricyclic system in numerous natural products, in particular the scaffold of tetrahydrocannabinol (THC) being the most representative one. Compared with other published methods, condensation with a preexisting cyclohexane moiety in the precursor is needed to gain the heterogenic tricycle systems, whereas we present a novel strategy towards cannabinoid derivatives based on a flexible modular synthesis.
- Braese, Stefan,Volz, Nicole,Glaeser, Franziska,Nieger, Martin
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p. 1385 - 1392
(2012/11/07)
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- Preparation of the MacMillan imidazolidinones
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A general method for the preparation of the MacMillan imidazolidinones is described. Treatment of an α-amino amide with a carbonyl compound in refluxing chloroform in the presence of Yb(OTf)3 (1 mol %) provides convenient access to the corresponding imidazolidinones.
- Samulis, Leopold,Tomkinson, Nicholas C.O.
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p. 4263 - 4267
(2011/06/26)
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- Synthesis of chiral γ-lactams via Rh(II) catalyzed intramolecular C-H insertion: α-substituents and conformational effects
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Highly functionalized chiral γ-lactams are efficiently synthesized via Rh(II) catalyzed intramolecular C-H insertion from various α-diazoamides. Independent of α-substituents, regio- and stereoselectivities are enhanced through a conformational effect exerted by a bicyclic transition state.
- Flanigan, David L.,Yoon, Cheol Hwan,Jung, Kyung Woon
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p. 143 - 146
(2007/10/03)
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- Enantioselective transformation of alpha,beta-unsaturated ketones using chiral organic catalysts
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Nonmetallic organic catalysts are provided that facilitate the enantioselective reaction of α,β-unsaturated ketones. The catalysts are chiral imidazolidinone compounds having the structure of formula (IIA) or (IIB) or are acid addition salts thereof, wherein, in one preferred embodiment, R1 is C1-C6 alkyl, R2is phenyl or 2-methylfuryl, R3 and R4 are hydrogen, and R5 is phenyl optionally substituted with 1 or 2 substituents selected from the group consisting of halo, hydroxyl, and C1-C6 alkyl The chiral imidazolidinones are useful in catalyzing a wide variety of reactions, including cycloaddition reactions, Friedel-Crafts alkylation reactions, and Michael additions.
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Page/Page column 10
(2008/06/13)
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- Chemical transformation of substrates using nonmetallic, organic catalyst compositions
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A method is provided for catalytically transforming a functional group within a first reactant by reaction with a second reactant in the presence of a nonmetallic, organic catalyst composition composed of a heteroatom-containing activator and an acid, or a salt of a heteroatom-containing activator and an acid. Exemplary first reactants are α,β-unsaturated carbonyl compounds such as α,β-unsaturated ketones and α,β-unsaturated aldehydes. The heteroatom of the activator is a Group 15 or Group 16 element such as nitrogen, oxygen, sulfur or phosphorus, and exemplary heteroatom-containing activators are amines. Chiral heteroatom-containing activators can be used to catalyze enantioselective reactions, such that a chiral product is obtained from a chiral or achiral starting material in enantiomerically pure form.
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- Influence des ultrasons sur la diastereoselectivite. Synthese d'imidazolidine-4-one chirales
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A three-step synthesis of imidazolidine-4-one has been realized.Sodium dithionite was a very efficient reagent for the last step, the reduction of a ketone.The reaction is slow under the normal conditions of heating and its diastereoselectivity is poor.Un
- Hubert, Cathy,Garrigues, Bernard
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p. 234 - 237
(2007/10/03)
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- 5-Substituted (5S)-Imidazolidin-4-ones as Effective Chiral Auxiliary for Hydrogenation of α-Keto Amides
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The title chiral auxiliary was used for asymmetric catalytic hydrogenation of amides derived from phenylglyoxylic acid to give mandelamides with high diastereoselectivity (diastereosisomeric excess, d.e. up to 96percent). Keywords.Asymmetric hydrogenation
- Solodin, Igor
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p. 565 - 570
(2007/10/02)
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- (5S)-5-Benzyl-2,2,3-trimethylimidazolidin-4-one as Highly Effective Chiral Auxiliary for Asymmetric Reduction of α-Oxo Amides
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Reduction of the α-oxo amide derived from phenylglyoxylic acid, containing (5S)-5-benzyl-2,2,3-trimethylimidazolidin-4-one as a chiral auxiliary, with NaBH4 or via fluoride ion-induced hydrosilylation with HSiMe2Ph was found to proceed with 90-100percent
- Solodin, Igor,Goldberg, Yuri,Zelcans, Gunars,Lukevics, Edmunds
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p. 1321 - 1322
(2007/10/02)
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