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Tchodimo FCM, Ermler WC. Theoretical and computational study of benzenium and toluenium isomers. Front Chem 2023; 11:1253599. [PMID: 38025065 PMCID: PMC10646329 DOI: 10.3389/fchem.2023.1253599] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 09/19/2023] [Indexed: 12/01/2023] Open
Abstract
Four methods of computational quantum chemistry are used in a study of hyperconjugation in protonated aromatic molecules. Benzene, benzenium, toluene, and four isomeric forms of toluenium are examined using the self-consistent field level of theory followed by configuration interaction and coupled cluster calculations, as well as density functional theory. Results for proton affinities, geometric parameters, atomic populations, dipole moments, and polarizabilities are reported. The calculated results are in good agreement with previous computational studies and with experimental data. The presence of hyperconjugation is evident from the shortened carbon-carbon bond lengths in the aromatic ring and concomitant changes in dipole moments and polarizabilities. The proton affinities of benzene and toluene compare well with experimental values. The examination of all of the toluenium isomers reveals that the position of the methyl group has a minor impact on the strength of hyperconjugation, although the most stable isomer is found to be the para form. Mulliken population analyses indicate that the addition of a proton contributes to aromatic hyperconjugation and increases the strength of π-bonds at the expense of σ-bonds.
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Affiliation(s)
| | - Walter C. Ermler
- Department of Chemistry, The University of Texas at San Antonio, San Antonio, TX, United States
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2
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Yus M, Nájera C, Foubelo F, Sansano JM. Metal-Catalyzed Enantioconvergent Transformations. Chem Rev 2023; 123:11817-11893. [PMID: 37793021 PMCID: PMC10603790 DOI: 10.1021/acs.chemrev.3c00059] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2023] [Indexed: 10/06/2023]
Abstract
Enantioconvergent catalysis has expanded asymmetric synthesis to new methodologies able to convert racemic compounds into a single enantiomer. This review covers recent advances in transition-metal-catalyzed transformations, such as radical-based cross-coupling of racemic alkyl electrophiles with nucleophiles or racemic alkylmetals with electrophiles and reductive cross-coupling of two electrophiles mainly under Ni/bis(oxazoline) catalysis. C-H functionalization of racemic electrophiles or nucleophiles can be performed in an enantioconvergent manner. Hydroalkylation of alkenes, allenes, and acetylenes is an alternative to cross-coupling reactions. Hydrogen autotransfer has been applied to amination of racemic alcohols and C-C bond forming reactions (Guerbet reaction). Other metal-catalyzed reactions involve addition of racemic allylic systems to carbonyl compounds, propargylation of alcohols and phenols, amination of racemic 3-bromooxindoles, allenylation of carbonyl compounds with racemic allenolates or propargyl bromides, and hydroxylation of racemic 1,3-dicarbonyl compounds.
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Affiliation(s)
- Miguel Yus
- Centro
de Innovación en Química Avanzada (ORFEO−CINQA), Universidad de Alicante, Apdo. 99, E-03080 Alicante, Spain
| | - Carmen Nájera
- Centro
de Innovación en Química Avanzada (ORFEO−CINQA), Universidad de Alicante, Apdo. 99, E-03080 Alicante, Spain
| | - Francisco Foubelo
- Centro
de Innovación en Química Avanzada (ORFEO−CINQA), Universidad de Alicante, Apdo. 99, E-03080 Alicante, Spain
- Departamento
de Química Orgánica and Instituto de Síntesis
Orgánica (ISO), Universidad de Alicante, Apdo. 99, E-03080 Alicante, Spain
| | - José M. Sansano
- Centro
de Innovación en Química Avanzada (ORFEO−CINQA), Universidad de Alicante, Apdo. 99, E-03080 Alicante, Spain
- Departamento
de Química Orgánica and Instituto de Síntesis
Orgánica (ISO), Universidad de Alicante, Apdo. 99, E-03080 Alicante, Spain
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3
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Yang ZP, Freas DJ, Fu GC. Asymmetric Synthesis of Protected Unnatural α-Amino Acids via Enantioconvergent Nickel-Catalyzed Cross-Coupling. J Am Chem Soc 2021; 143:8614-8618. [PMID: 34080836 DOI: 10.1021/jacs.1c03903] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Interest in unnatural α-amino acids has increased rapidly in recent years in areas ranging from protein design to medicinal chemistry to materials science. Consequently, the development of efficient, versatile, and straightforward methods for their enantioselective synthesis is an important objective in reaction development. In this report, we establish that a chiral catalyst based on nickel, an earth-abundant metal, can achieve the enantioconvergent coupling of readily available racemic alkyl electrophiles with a wide variety of alkylzinc reagents (1:1.1 ratio) to afford protected unnatural α-amino acids in good yield and ee. This cross-coupling, which proceeds under mild conditions and is tolerant of air, moisture, and a broad array of functional groups, complements earlier approaches to the catalytic asymmetric synthesis of this valuable family of molecules. We have applied our new method to the generation of several enantioenriched unnatural α-amino acids that have previously been shown to serve as useful intermediates in the synthesis of bioactive compounds.
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Affiliation(s)
- Ze-Peng Yang
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Dylan J Freas
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Gregory C Fu
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
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Roche SP. In the Pursuit of (Ald)Imine Surrogates for the Direct Asymmetric Synthesis of Non-Proteinogenic α-Amino Acids. SYNTHESIS-STUTTGART 2021. [DOI: 10.1055/a-1463-4266] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
AbstractNature remarkably employs posttranslational modifications of the 20 canonical α-amino acids to devise a far larger structural, conformational, and functional diversity found in non-proteinogenic amino acids (NPAAs), which ultimately translates into a plethora of complex biological functions. Synthetic chemists are continuously trying to reproduce and even extrapolate the repertoire of NPAA building blocks to build structural diversity into bioactive molecules and materials. The direct asymmetric functionalization of α-imino esters represents one of the most robust and attractive routes to NPAAs. This review summarizes the most prominent examples of bench-stable (ald)imine surrogates exploited for the synthesis of NPAAs, including our most recent results in the nucleophilic substitution of α-haloglycines and other α-haloaminals. A synopsis of kinetic studies, reaction optimizations, and enantioselective catalytic methods is also presented.1 Introduction2 Asymmetric Synthesis of Tertiary α-Substituted NPAAs2.1 From N,O-Acetals (α-Hydroxy/Alkyloxy/Acetoxyglycines)2.2 From α-Amido Sulfones2.3 From α-Haloglycine Esters2.4 From N,O-Bis(Boc) Hydroxyglycine3 Asymmetric Synthesis of Acyclic Quaternary α,α-Disubstituted NPAAs4 Concluding Remarks
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Affiliation(s)
- Stéphane P. Roche
- Department of Chemistry and Biochemistry, Florida Atlantic University
- Center for Molecular Biology and Biotechnology, Florida Atlantic University
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5
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Xu H, Nazli A, Zou C, Wang ZP, He Y. Bench-stable imine surrogates for the one-pot and catalytic asymmetric synthesis of α-amino esters/ketones. Chem Commun (Camb) 2020; 56:14243-14246. [PMID: 33118565 DOI: 10.1039/d0cc06055k] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
N,O-Bis(tert-butoxycarbonyl)hydroxylamines are readily accessible as imine surrogates, which are bench stable and could quantitatively generate the corresponding imines for in situ applications. An unpresented catalytic asymmetric method for the synthesis of α-amino esters and ketones from novel imine surrogates, N,O-bis(tert-butoxycarbonyl)hydroxylamines, as well as its preliminary mechanistic studies are reported. A variety of optically enriched products were obtained in excellent yields and enantioselectivities (up to 99% yield and >99% ee).
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Affiliation(s)
- Huacheng Xu
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, School of Pharmaceutical Sciences, Chongqing University, Chongqing, 401331, P. R. China.
| | - Adila Nazli
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, School of Pharmaceutical Sciences, Chongqing University, Chongqing, 401331, P. R. China.
| | - Cheng Zou
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, School of Pharmaceutical Sciences, Chongqing University, Chongqing, 401331, P. R. China.
| | - Zhi-Peng Wang
- Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing, 400714, P. R. China.
| | - Yun He
- Chongqing Key Laboratory of Natural Product Synthesis and Drug Research, School of Pharmaceutical Sciences, Chongqing University, Chongqing, 401331, P. R. China.
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Zhao G, Samanta SS, Michieletto J, Roche SP. A Broad Substrate Scope of Aza-Friedel-Crafts Alkylation for the Synthesis of Quaternary α-Amino Esters. Org Lett 2020; 22:5822-5827. [PMID: 32649206 PMCID: PMC7654210 DOI: 10.1021/acs.orglett.0c01895] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A versatile synthetic protocol of aza-Friedel-Crafts alkylation has been developed for the synthesis of quaternary α-amino esters. This operationally simple alkylation proceeds under ambient conditions with high efficiency, regioselectivity, and an exceptionally broad scope of arene nucleophiles. A key feature of this alkylation is the role associated with the silver(I) salt counteranions liberated during the reaction. Taking advantage of a phase-transfer counteranion/Brønsted acid pair mechanism, we also report a catalytic enantioselective example of the reaction.
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Affiliation(s)
- Guangkuan Zhao
- Department of Chemistry and Biochemistry, Florida Atlantic University, Boca Raton, Florida 33431, United States
| | - Shyam S Samanta
- Department of Chemistry and Biochemistry, Florida Atlantic University, Boca Raton, Florida 33431, United States
| | - Jessica Michieletto
- Department of Chemistry and Biochemistry, Florida Atlantic University, Boca Raton, Florida 33431, United States
| | - Stéphane P Roche
- Department of Chemistry and Biochemistry, Florida Atlantic University, Boca Raton, Florida 33431, United States
- Center for Molecular Biology and Biotechnology, Florida Atlantic University, Jupiter, Florida 33458, United States
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