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Ara H Mermerian - One of the best experts on this subject based on the ideXlab platform.
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catalytic enantioselective construction of all carbon quaternary stereocenters synthetic and mechanistic studies of the c acylation of silyl ketene acetals
Journal of the American Chemical Society, 2005Co-Authors: Ara H MermerianAbstract:With the aid of an appropriate chiral catalyst, acyclic silyl ketene acetals react with Anhydrides to furnish 1,3-dicarbonyl compounds that bear all-carbon quaternary stereocenters in good ee and yield. Mechanistic studies provide strong support for a catalytic cycle that involves activation of both the electrophile (Anhydride → acylpyridinium) and the nucleophile (silyl ketene acetal → enolate).
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catalytic enantioselective synthesis of quaternary stereocenters via intermolecular c acylation of silyl ketene acetals dual activation of the electrophile and the nucleophile
Journal of the American Chemical Society, 2003Co-Authors: Ara H MermerianAbstract:A nucleophile-catalyzed asymmetric intermolecular C-acylation of silyl ketene acetals by Anhydrides has been developed, furnishing quaternary stereocenters with high enantioselectivity. Mechanistic studies support the hypothesis that the reaction involves activation both of the silyl ketene acetal (generation of an enolate) and of the Anhydride (formation of an acylpyridinium ion).
Rob Duchateau - One of the best experts on this subject based on the ideXlab platform.
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semi aromatic polyesters by alternating ring opening copolymerisation of styrene oxide and Anhydrides
Polymer Chemistry, 2012Co-Authors: Elham Hosseini Nejad, Anita Paoniasari, C Cor E Koning, Rob DuchateauAbstract:Ring-opening copolymerisation of styrene oxide with alicyclic Anhydrides containing different ring strains (succinic Anhydride, maleic Anhydride, citraconic Anhydride, cyclopropane-1,2-dicarboxylic acid Anhydride, cyclopentane-1,2-dicarboxylic acid Anhydride and phthalic Anhydride) was performed applying metal salen and tetraphenyl porphyrin complexes where for (salen)MX, M = Cr, X = Cl (1), M = Al, X = Cl (2), M = Mn, X = Cl (3), M = Co, X = OAc (4) and salen = N,N-bis(3,5-di-tert-butylsalicylidene)-diimine and for porphyrin complex, M = Cr, X = Cl (5), M = Mn, X = Cl (6), M = Co, X = OAc (7). The chromium catalysts performed best and therefore 1 was chosen as the selected catalyst for further studies. Investigation of the effect of different cocatalysts on the copolymerisation of styrene oxide and phthalic Anhydride revealed that phosphines and onium salt showed quite similar activities whereas N-heterocyclic based amines showed somewhat lower activity. 1H NMR and MALDI-ToF-MS spectra of the copolymers formed confirmed the alternating microstructures. Increasing the monomer to catalyst ratio resulted in the isomerisation of styrene oxide to phenyl ethanal. The aldehyde functions as a chain transfer agent influencing the molecular weight of the polymers. Copolymerisation of styrene oxide with Anhydrides bearing a double bond in their structure, such as maleic Anhydride and citraconic Anhydride, was shown to be highly dependent on temperature, time, type of cocatalyst and solvent used in the copolymerisation reaction.
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ring opening co and terpolymerization of an alicyclic oxirane with carboxylic acid Anhydrides and co2 in the presence of chromium porphyrinato and salen catalysts
Macromolecules, 2011Co-Authors: Saskia Huijser, C Cor E Koning, Elham Hosseininejad, R Rafael J Sablong, Chris De Jong, Rob DuchateauAbstract:Copolymerization of cyclohexene oxide (CHO) with alicyclic Anhydrides applying chromium tetraphenylprophyrinato (TPPCrCl, 1) and salophen (SalophenCrCl, 2) catalysts resulted in polyesters or poly(ester-co-ether)s, depending on the nature of the catalyst, presence of a cocatalyst, solvent and type of Anhydride. The combination of 1 as catalyst and 4-N,N-dimethylamino-pyridine (DMAP) as cocatalyst in the copolymerization of CHO with succinic Anhydride (SA), cyclopropane-1,2-dicarboxylic acid Anhydride (CPrA), cyclopentane-1,2-dicarboxylic acid Anhydride (CPA) or phthalic Anhydride (PA) invariably resulted in a completely alternating topology and therefore a pure polyester. Contrarily, 2 in combination with DMAP did not afford pure polyesters for the copolymerization of CHO with SA or CPrA but did render the alternating topology when CPA or PA was used as Anhydride comonomer. Water proved to be an efficient bifunctional CTA affording α,ω-hydroxyl-terminated polyesters without loss of catalytic activity. Whe...
Isamu Shiina - One of the best experts on this subject based on the ideXlab platform.
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kinetic resolution of racemic α hydroxyphosphonates by asymmetric esterification using achiral carboxylic acids with pivalic Anhydride and a chiral acyl transfer catalyst
ChemInform, 2014Co-Authors: Isamu Shiina, Keisuke Ono, Takayoshi NakaharaAbstract:A practical protocol is developed to directly provide chiral α-acyloxyphosphonates and α-hydroxyphosphonates from (±)-α-hydroxyphosphonates utilizing the transacylation process to generate the mixed Anhydrides from acid components and pivalic Anhydride in the presence of organocatalysts (s-value = 33–518).
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kinetic resolution of racemic α arylalkanoic acids with achiral alcohols via the asymmetric esterification using carboxylic Anhydrides and acyl transfer catalysts
Journal of the American Chemical Society, 2010Co-Authors: Isamu Shiina, Kenya Nakata, Keisuke Ono, Yu Suke Onda, Makoto ItagakiAbstract:A variety of optically active carboxylic esters are produced by the kinetic resolution of racemic α-substituted carboxylic acids using achiral alcohols, aromatic or aliphatic carboxylic Anhydrides, and chiral acyl-transfer catalysts. The combination of 4-methoxybenzoic Anhydride (PMBA) or pivalic Anhydride with the modified benzotetramisole-type catalyst ((S)-β-Np-BTM) is the most effective for promotion of the enantioselective coupling reaction between racemic carboxylic acids and a novel nucleophile, bis(α-naphthyl)methanol, to give the corresponding esters with high ee’s. This protocol was successfully applied to the production of nonracemic nonsteroidal anti-inflammatory drugs from racemic compounds utilizing the transacylation process to generate the mixed Anhydrides from the acid components with the suitable carboxylic Anhydrides.
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kinetic resolution of the racemic 2 hydroxyalkanoates using the enantioselective mixed Anhydride method with pivalic Anhydride and a chiral acyl transfer catalyst
Chemistry: A European Journal, 2010Co-Authors: Isamu Shiina, Kenya Nakata, Keisuke Ono, Masuhiro Sugimoto, Akihiro SekiguchiAbstract:A variety of optically active 2-hydroxyalkanoates and the corresponding 2-acyloxyalkanoates are produced by the kinetic resolution of racemic 2-hydroxyalkanoates by using achiral 2,2-diarylacetic acid with hindered carboxylic Anhydrides as the coupling reagents. The combined use of diphenylacetic acid, pivalic Anhydride, and (+)-(R)-benzotetramisole ((R)-BTM) effectively produces (S)-2-hydroxyalkanoates and (R)-2-acyloxyalkanoates from the racemic 2-hydroxyalkanoates (s-values=47-202). This protocol directly provides the desired chiral 2-hydroxyalkanoate derivatives from achiral diarylacetic acid and racemic secondary alcohols that do not include the sec-phenethyl alcohol moiety by using the transacylation process to generate the mixed Anhydrides from the acid components with bulky carboxylic Anhydrides under the influence of the chiral acyl-transfer catalyst. The transition state that provides the desired (R)-2-acyloxyalkanoate from (R)-2-hydroxyalkanoate included in the racemic mixture is disclosed by DFT calculations, and the structural features of the transition form are also discussed.
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2 6 dimethyl 4 nitrobenzoic Anhydride dmnba an effective coupling reagent for the synthesis of carboxylic esters and lactones
Heterocycles, 2008Co-Authors: Isamu Shiina, Ryo MiyaoAbstract:Various carboxylic esters are obtained at room temperature in excellent yields with high chemoselectivities from nearly equimolar amounts of carboxylic acids and alcohols using 2,6-dimethyl-4-nitrobenzoic Anhydride with triethylamine by the promotion of 4-(dimethylamino)pyridine. The efficiency of the esterification is compared to those of other dehydrations using substituted benzoic Anhydrides as coupling reagents. This method was successfully applied to the synthesis of threo-aleuritic acid lactone and the desired 17-membered ring compound was prepared in high yield at room temperature from the corresponding free trihydroxycarboxylic acid using 2,6-dimethyl-4-nitrobenzoic Anhydride in the presence of 4-(dimethylamino)pyridine.
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the first asymmetric esterification of free carboxylic acids with racemic alcohols using benzoic Anhydrides and tetramisole derivatives an application to the kinetic resolution of secondary benzylic alcohols
Tetrahedron Letters, 2007Co-Authors: Isamu Shiina, Kenya NakataAbstract:Abstract A variety of optically active carboxylic esters are produced by the kinetic resolution of racemic secondary benzylic alcohols using free carboxylic acids with benzoic Anhydride and tetramisole derivatives. 4-Methoxybenzoic Anhydride (PMBA) is the best reagent to use in producing the corresponding esters in high ee when the reaction is catalyzed by (+)-benzotetramisole (BTM); by contrast, when non-substituted benzoic Anhydride is used as a coupling reagent, the resulting optically active alcohols are obtained with high selectivities. This protocol directly produces chiral carboxylic esters from free carboxylic acids and racemic secondary alcohols by utilizing the trans-acylation process to generate mixed Anhydrides from acid components and benzoic Anhydride derivatives under the influence of chiral catalysts.
C Cor E Koning - One of the best experts on this subject based on the ideXlab platform.
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semi aromatic polyesters by alternating ring opening copolymerisation of styrene oxide and Anhydrides
Polymer Chemistry, 2012Co-Authors: Elham Hosseini Nejad, Anita Paoniasari, C Cor E Koning, Rob DuchateauAbstract:Ring-opening copolymerisation of styrene oxide with alicyclic Anhydrides containing different ring strains (succinic Anhydride, maleic Anhydride, citraconic Anhydride, cyclopropane-1,2-dicarboxylic acid Anhydride, cyclopentane-1,2-dicarboxylic acid Anhydride and phthalic Anhydride) was performed applying metal salen and tetraphenyl porphyrin complexes where for (salen)MX, M = Cr, X = Cl (1), M = Al, X = Cl (2), M = Mn, X = Cl (3), M = Co, X = OAc (4) and salen = N,N-bis(3,5-di-tert-butylsalicylidene)-diimine and for porphyrin complex, M = Cr, X = Cl (5), M = Mn, X = Cl (6), M = Co, X = OAc (7). The chromium catalysts performed best and therefore 1 was chosen as the selected catalyst for further studies. Investigation of the effect of different cocatalysts on the copolymerisation of styrene oxide and phthalic Anhydride revealed that phosphines and onium salt showed quite similar activities whereas N-heterocyclic based amines showed somewhat lower activity. 1H NMR and MALDI-ToF-MS spectra of the copolymers formed confirmed the alternating microstructures. Increasing the monomer to catalyst ratio resulted in the isomerisation of styrene oxide to phenyl ethanal. The aldehyde functions as a chain transfer agent influencing the molecular weight of the polymers. Copolymerisation of styrene oxide with Anhydrides bearing a double bond in their structure, such as maleic Anhydride and citraconic Anhydride, was shown to be highly dependent on temperature, time, type of cocatalyst and solvent used in the copolymerisation reaction.
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alternating ring opening polymerization of cyclohexene oxide and Anhydrides effect of catalyst cocatalyst and Anhydride structure
Macromolecules, 2012Co-Authors: Elham Hosseini Nejad, C Cor E Koning, Cgw Carlo Van Melis, T Tim J Vermeer, Robbert DuchateauAbstract:Ring-opening copolymerization of cyclohexene oxide with alicyclic Anhydrides containing different ring strain (succinic Anhydride, cyclopropane-1,2-dicarboxylic acid Anhydride, and phthalic Anhydride) was performed applying metal salen chloride complexes, (salen)MCl (M = Al, Cr, Co; salen = N,N-bis(3,5-di-tert-butylsalicylidene)diimine) with different metals and ligand–diimine backbones. While some of the bulk copolymerizations afforded poly(ester-co-ether)s, all solution polymerizations produced perfect alternating copolymers. The chromium catalysts performed best while the aluminum catalysts were the least active ones. For each metal, the salophen complexes yielded the best performing catalyst. A variety of cocatalysts have been employed: bis(triphenylphosphoranylidene)ammonium chloride, N-heterocyclic nucleophiles including 4-(dimethylamino)pyridine, N-methylimidazole, and 1,5,7-triazabicyclododecene and the phosphines trimesitylphosphine, tris(2,4,6-trimethoxyphenyl)phosphine, tricyclohexylphosphine t...
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ring opening co and terpolymerization of an alicyclic oxirane with carboxylic acid Anhydrides and co2 in the presence of chromium porphyrinato and salen catalysts
Macromolecules, 2011Co-Authors: Saskia Huijser, C Cor E Koning, Elham Hosseininejad, R Rafael J Sablong, Chris De Jong, Rob DuchateauAbstract:Copolymerization of cyclohexene oxide (CHO) with alicyclic Anhydrides applying chromium tetraphenylprophyrinato (TPPCrCl, 1) and salophen (SalophenCrCl, 2) catalysts resulted in polyesters or poly(ester-co-ether)s, depending on the nature of the catalyst, presence of a cocatalyst, solvent and type of Anhydride. The combination of 1 as catalyst and 4-N,N-dimethylamino-pyridine (DMAP) as cocatalyst in the copolymerization of CHO with succinic Anhydride (SA), cyclopropane-1,2-dicarboxylic acid Anhydride (CPrA), cyclopentane-1,2-dicarboxylic acid Anhydride (CPA) or phthalic Anhydride (PA) invariably resulted in a completely alternating topology and therefore a pure polyester. Contrarily, 2 in combination with DMAP did not afford pure polyesters for the copolymerization of CHO with SA or CPrA but did render the alternating topology when CPA or PA was used as Anhydride comonomer. Water proved to be an efficient bifunctional CTA affording α,ω-hydroxyl-terminated polyesters without loss of catalytic activity. Whe...
Kenya Nakata - One of the best experts on this subject based on the ideXlab platform.
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kinetic resolution of racemic α arylalkanoic acids with achiral alcohols via the asymmetric esterification using carboxylic Anhydrides and acyl transfer catalysts
Journal of the American Chemical Society, 2010Co-Authors: Isamu Shiina, Kenya Nakata, Keisuke Ono, Yu Suke Onda, Makoto ItagakiAbstract:A variety of optically active carboxylic esters are produced by the kinetic resolution of racemic α-substituted carboxylic acids using achiral alcohols, aromatic or aliphatic carboxylic Anhydrides, and chiral acyl-transfer catalysts. The combination of 4-methoxybenzoic Anhydride (PMBA) or pivalic Anhydride with the modified benzotetramisole-type catalyst ((S)-β-Np-BTM) is the most effective for promotion of the enantioselective coupling reaction between racemic carboxylic acids and a novel nucleophile, bis(α-naphthyl)methanol, to give the corresponding esters with high ee’s. This protocol was successfully applied to the production of nonracemic nonsteroidal anti-inflammatory drugs from racemic compounds utilizing the transacylation process to generate the mixed Anhydrides from the acid components with the suitable carboxylic Anhydrides.
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kinetic resolution of the racemic 2 hydroxyalkanoates using the enantioselective mixed Anhydride method with pivalic Anhydride and a chiral acyl transfer catalyst
Chemistry: A European Journal, 2010Co-Authors: Isamu Shiina, Kenya Nakata, Keisuke Ono, Masuhiro Sugimoto, Akihiro SekiguchiAbstract:A variety of optically active 2-hydroxyalkanoates and the corresponding 2-acyloxyalkanoates are produced by the kinetic resolution of racemic 2-hydroxyalkanoates by using achiral 2,2-diarylacetic acid with hindered carboxylic Anhydrides as the coupling reagents. The combined use of diphenylacetic acid, pivalic Anhydride, and (+)-(R)-benzotetramisole ((R)-BTM) effectively produces (S)-2-hydroxyalkanoates and (R)-2-acyloxyalkanoates from the racemic 2-hydroxyalkanoates (s-values=47-202). This protocol directly provides the desired chiral 2-hydroxyalkanoate derivatives from achiral diarylacetic acid and racemic secondary alcohols that do not include the sec-phenethyl alcohol moiety by using the transacylation process to generate the mixed Anhydrides from the acid components with bulky carboxylic Anhydrides under the influence of the chiral acyl-transfer catalyst. The transition state that provides the desired (R)-2-acyloxyalkanoate from (R)-2-hydroxyalkanoate included in the racemic mixture is disclosed by DFT calculations, and the structural features of the transition form are also discussed.
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the first asymmetric esterification of free carboxylic acids with racemic alcohols using benzoic Anhydrides and tetramisole derivatives an application to the kinetic resolution of secondary benzylic alcohols
Tetrahedron Letters, 2007Co-Authors: Isamu Shiina, Kenya NakataAbstract:Abstract A variety of optically active carboxylic esters are produced by the kinetic resolution of racemic secondary benzylic alcohols using free carboxylic acids with benzoic Anhydride and tetramisole derivatives. 4-Methoxybenzoic Anhydride (PMBA) is the best reagent to use in producing the corresponding esters in high ee when the reaction is catalyzed by (+)-benzotetramisole (BTM); by contrast, when non-substituted benzoic Anhydride is used as a coupling reagent, the resulting optically active alcohols are obtained with high selectivities. This protocol directly produces chiral carboxylic esters from free carboxylic acids and racemic secondary alcohols by utilizing the trans-acylation process to generate mixed Anhydrides from acid components and benzoic Anhydride derivatives under the influence of chiral catalysts.