Showing papers by "Keiji Maruoka published in 2012"
TL;DR: Catalytic asymmetric synthesis of axially chiral o-iodoacrylanilides and N-allyl-o-iodoanilides as useful chiral building blocks was achieved via chiral quaternary ammonium salt-catalyzed N-alkylations under phase-transfer conditions.
Abstract: Catalytic asymmetric synthesis of axially chiral o-iodoacrylanilides and N-allyl-o-iodoanilides as useful chiral building blocks was achieved via chiral quaternary ammonium salt-catalyzed N-alkylations under phase-transfer conditions. The transition-state structure for the present reaction is discussed on the basis of the X-ray crystal structure of ammonium anilide.
124 citations
TL;DR: This organocatalytic process represents the first example of a Mannich reaction using Z- or Boc-protected aminoacetaldehyde as a new entry of α-nitrogen functionalized aldehyde nucleophile in enamine catalysis.
Abstract: The 1,2-diamine (vicinal diamine) motif is present in a number of natural products with interesting biological activity and in many chiral molecular catalysts. The efficient and stereocontrolled synthesis of enantioenriched vicinal diamines is still a challenge to modern chemical methodology. We report here both syn- and anti-selective asymmetric direct Mannich reactions of N-protected aminoacetaldehydes with N-Boc-protected imines catalyzed by proline and the axially chiral amino sulfonamide (S)-3. This organocatalytic process represents the first example of a Mannich reaction using Z- or Boc-protected aminoacetaldehyde as a new entry of α-nitrogen functionalized aldehyde nucleophile in enamine catalysis. The obtained optically active vicinal diamines are useful chiral synthons as exemplified by the formal synthesis of (-)-agelastatin A.
105 citations
85 citations
TL;DR: An unconventional Ugi: A catalytic asymmetric Ugi-type reaction can be realized by use of N'-alkylbenzohydrazide, instead of a conventional amine, in the presence of an axially chiral dicarboxylic acid.
Abstract: An unconventional Ugi: A catalytic asymmetric Ugi-type reaction can be realized by use of N'-alkylbenzohydrazide, instead of a conventional amine, in the presence of an axially chiral dicarboxylic acid. The reaction proceeds through a key acyclic azomethine imine intermediate, which has recently emerged as a promising electrophile in asymmetric catalysis.
75 citations
72 citations
TL;DR: Enantioselective direct aldol reaction of α-substituted nitroacetates with aqueous formaldehyde for the synthesis ofα-alkyl serines has been achieved under base-free neutral phase- transfer conditions with a bifunctional chiral phase-transfer catalyst.
Abstract: Enantioselective direct aldol reaction of α-substituted nitroacetates with aqueous formaldehyde for the synthesis of α-alkyl serines has been achieved under base-free neutral phase-transfer conditions with a bifunctional chiral phase-transfer catalyst.
59 citations
TL;DR: Di-tert-butyl methylenemalonate could be employed as a reactive equivalent of a three-carbon Michael acceptor such as acrylate in a direct asymmetric conjugate addition of aldehydes catalyzed by an axially chiral amino diol catalyst (S)-3a.
Abstract: Di-tert-butyl methylenemalonate (1) could be employed as a reactive equivalent of a three-carbon Michael acceptor such as acrylate in a direct asymmetric conjugate addition of aldehydes catalyzed by an axially chiral amino diol (S)-3a. Furthermore, acrylate, an unexplored and challenging substrate in enamine catalysis, has also been successfully employed in asymmetric conjugate addition reaction. Relatively inert acrylate is doubly activated by polyfluoroalkyl group of 2 and the hydroxyl group on the axially chiral amino diol catalyst (S)-3b, giving corresponding conjugate adducts in high yield with excellent enantiomeric excess. The obtained conjugate addition products were readily converted to synthetically useful and important chiral building blocks.
38 citations
TL;DR: In this article, a chiral phase-transfer catalyst possessing a 6,6′-bridged ring on the biphenyl unit has been developed for the practical synthesis of α,α-dialkyl-α-amino acids.
22 citations
TL;DR: A diastereo- and enantioselective aldol reaction between aldehydes and a synthetically useful ketomalonate 1c as a hydrated form was developed and either anti- or syn-aldol adducts having a chiral tetrasubstituted carbon center were obtained in high enantiOSElectivities.
21 citations
TL;DR: Conformationally constrained cyclic amino acids have played an important role in peptide-based drug design and the development of new methods for stereoselective synthesis of these compounds is an important task for synthetic organic chemistry.
Abstract: Conformationally constrained cyclic amino acids have played an important role in peptide-based drug design. Hence, the development of new methods for stereoselective synthesis of these compounds is an important task for synthetic organic chemistry. 3] Among cyclic amino acids, bicyclic amino acid 1 is an important synthetic target for pharmaceutical industry (Figure 1), because it is a core structure of telaprevir, which is
19 citations
TL;DR: The communications and feature articles in this web collection cover important up-to-date information on organocatalysis, and sketch the fruitful development of this exciting field.
TL;DR: In this paper, the development of axially chiral dicarboxylic acid catalyzed desymmetrizing asymmetric semipinacol rearrangement of symmetrically substituted six-membered cyclic β-hydroxy-α-diazo esters is reported as a means to give chiral cycloheptanones with good enantioselectivities.
TL;DR: In this article, a catalytic amount of lipophilic 18-crown-6 ether BBC in a biphasic H2O/toluene KCl solution was successfully applied for several conjugate addition reactions.
Abstract: A catalytic amount of lipophilic 18-crown-6 ether BBC in a biphasic H2O/toluene KCl solution is successfully applied for several conjugate addition reactions.
TL;DR: In this article, a chiral phase-transfer-catalyzed asymmetric conjugate addition of N-(diphenylmethylene)glycine ester to α,β-unsaturated aldehydes was used to synthesize trans-3-substituted proline derivatives with high enantioselectivity.
TL;DR: In this article, a series of chiral quaternary ammonium salts derived from commercially available (R)- or (S)-binaphthol have been designed as new C 2 -symmetric chiral phase-transfer cata- lysts.
Abstract: A series of chiral quaternary ammonium salts derived from commercially available (R)- or (S)-binaphthol have been designed as new C 2 -symmetric chiral phase-transfer cata- lysts. In order to realize the flexible design of these phase-transfer catalysts, the combinato- rial design approach has been developed. Chiral high-performance organocatalysts, thus obtained, have been successfully applied to the highly practical asymmetric synthesis of var- ious amino acid derivatives, including α-alkyl and α,α-dialkyl-α-amino acids in addition to alkaloids. Furthermore, several chiral bifunctional phase-transfer catalysts have been designed and synthesized for effecting base-free phase-transfer reactions under essentially neutral conditions in order to realize green sustainable chemistry.
01 Jan 2012
TL;DR: Water in organic synthesis as mentioned in this paper is a rapidly progressing field and a critical review of aqueous reactions by 47 experts is given in the reference work, which illustrates how water can often be a viable and green solvent in the laboratory.
Abstract: * Comprehensive overview of a rapidly progressing field * Critical review of aqueous reactions by 47 experts * Covering almost all types of organic reactions * Including special techniques with water and industrial applications * Emphasis on environmental aspects Water in Organic Synthesis is essential for the organic chemist in helping gain a thorough appreciation of the latest and most reliable available methods for using water in organic synthesis. It illustrates how water can often be a viable and green solvent in the laboratory and provides a detailed introduction to the subject: background information, evaluated methods, practical applications, industrial applications, special techniques, and an overview of the latest trends. The reference work also helps in inspiring chemists worldwide to find new approaches and techniques for the application of water in organic synthesis. Further information (including sample pages and the table of contents) General information about Science of Synthesis
TL;DR: The characteristic DEFGH-ring system of type B physalins has been synthesized by means of a one-pot procedure incorporating domino-type ring transformations and it is found that introduction of an α-hydroxyester functionality at C17 in ring E allowed the key 7-endo oxy-Michael reaction to proceed.
23 Aug 2012
TL;DR: The use of organoaluminum-based Lewis acids in the period 2000 to mid-2011 is overviewed with a focus on: (1) stoichiometric reactions in which one of the organo-aluminum substituents is transferred to the substrate (e.g., the opening of epoxides, 1,2-additions to carbonyl compounds, coupling with C-X, and Reissert chemistry) and (2) asymmetric, often catalytic, reactions promoted by Lewis acid catalysts derived from organo aluminum species (i.e
Abstract: The use of organoaluminum-based Lewis acids (AlRnX3–n; R 1⁄4 alkyl, alkynyl, X 1⁄4 halide or pseudohalide) in the period 2000 to mid-2011 is overviewed with a focus on: (1) stoichiometric reactions in which one of the organoaluminum substituents is transferred to the substrate (e.g., the opening of epoxides, 1,2-additions to carbonyl compounds, coupling with C–X, and Reissert chemistry) and (2) asymmetric, often catalytic, reactions promoted by Lewis acid catalysts derived from organoaluminum species (e.g., use of auxiliaries with alanes, Diels–Alder, and related cycloaddition reactions, additions to aldehydes and ketones, and skeletal rearrangement reactions).
TL;DR: In this article, a chiral quaternary ammonium salt-catalyzed N-alkylation under phase-transfer conditions is described, and the transition-state structure for the present reaction is discussed on the basis of the X-ray crystal structure of ammonium anilide.
Abstract: Catalytic asymmetric synthesis of axially chiral o-iodoacrylanilides and N-allyl-o-iodoanilides as useful chiral building blocks was achieved via chiral quaternary ammonium salt-catalyzed N-alkylations under phase-transfer conditions. The transition-state structure for the present reaction is discussed on the basis of the X-ray crystal structure of ammonium anilide.
TL;DR: In this paper, a diastereo and enantioselective conjugate addition of α-substituted nitroacetates to maleimides under base-free neutral phase-transfer conditions was developed for the synthesis of α,α-disubstitized α-amino acid derivatives.
Abstract: Highly diastereo- and enantioselective conjugate addition of α-substituted nitroacetates to maleimides under base-free neutral phase-transfer conditions was developed for the synthesis of α,α-disubstituted α-amino acid derivatives.
TL;DR: In the presence of the amine BPA, the syn adducts are mainly formed, while with L-proline the anti products are predominantly obtained.
Abstract: In the presence of the amine BPA, the syn adducts are mainly formed, while with L-proline the anti products are predominantly obtained.
TL;DR: In this paper, a series of chiral quaternary ammonium salts derived from commercially available (R)- or (S)-binaphthol have been designed as new C 2 -symmetric chiral phase-transfer cata- lysts.
Abstract: A series of chiral quaternary ammonium salts derived from commercially available (R)- or (S)-binaphthol have been designed as new C 2 -symmetric chiral phase-transfer cata- lysts. In order to realize the flexible design of these phase-transfer catalysts, the combinato- rial design approach has been developed. Chiral high-performance organocatalysts, thus obtained, have been successfully applied to the highly practical asymmetric synthesis of var- ious amino acid derivatives, including α-alkyl and α,α-dialkyl-α-amino acids in addition to alkaloids. Furthermore, several chiral bifunctional phase-transfer catalysts have been designed and synthesized for effecting base-free phase-transfer reactions under essentially neutral conditions in order to realize green sustainable chemistry.
TL;DR: In this paper, a chiral biphenyl catalysts with a 6,6′-bridged ring was designed and successfully applied to the enantioselective synthesis of amino acids having a quaternary stereocenter.
Abstract: Powerful chiral biphenyl catalysts possessing a 6,6′-bridged ring on the biphenyl unit are designed and successfully applied to the enantioselective synthesis of amino acids having a quaternary stereocenter.
TL;DR: A catalytic amount of lipophilic 18-crown-6 ether BBC in a biphasic H2O/toluene KCl solution is successfully applied for several conjugate addition reactions.
Abstract: A catalytic amount of lipophilic 18-crown-6 ether BBC in a biphasic H2O/toluene KCl solution is successfully applied for several conjugate addition reactions.
TL;DR: The asymmetric aldol reaction of malonate (I) with aldehydes (II) in the presence of an L-proline tetrazole analogue as a catalyst leads to alcohols (III), whilst the use of a chiral dibenzo[c,e]azepine catalyst (DMBAT) affords diastereomers (V).
Abstract: The asymmetric aldol reaction of malonate (I) with aldehydes (II) in the presence of an L-proline tetrazole analogue as a catalyst leads to alcohols (III), whilst the use of a chiral dibenzo[c,e]azepine catalyst (DMBAT) affords diastereomers (V).
TL;DR: In this paper, a bifunctional chiral phase-transfer organocatalyst was used to obtain a title reaction in the presence of a chiral CHO in terms of the phase transfer.
Abstract: Title reaction proceeds readily in the presence of a bifunctional chiral phase-transfer organocatalyst.