1
|
Chan SC, Palone A, Bietti M, Costas M. tert-Butyl as a Functional Group: Non-Directed Catalytic Hydroxylation of Sterically Congested Primary C-H Bonds. Angew Chem Int Ed Engl 2024; 63:e202402858. [PMID: 38688859 DOI: 10.1002/anie.202402858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2024] [Revised: 04/29/2024] [Accepted: 04/30/2024] [Indexed: 05/02/2024]
Abstract
The tert-butyl group is a common aliphatic motif extensively employed to implement steric congestion and conformational rigidity in organic and organometallic molecules. Because of the combination of a high bond dissociation energy (~100 kcal mol-1) and limited accessibility, in the absence of directing groups, neither radical nor organometallic approaches are effective for the chemical modification of tert-butyl C-H bonds. Herein we overcome these limits by employing a highly electrophilic manganese catalyst, [Mn(CF3bpeb)(OTf)2], that operates in the strong hydrogen bond donor solvent nonafluoro-tert-butyl alcohol (NFTBA) and catalytically activates hydrogen peroxide to generate a powerful manganese-oxo species that effectively oxidizes tert-butyl C-H bonds. Leveraging on the interplay of steric, electronic, medium and torsional effects, site-selective and product chemoselective hydroxylation of the tert-butyl group is accomplished with broad reaction scope, delivering primary alcohols as largely dominant products in preparative yields. Late-stage hydroxylation at tert-butyl sites is demonstrated on 6 densely functionalized molecules of pharmaceutical interest. This work uncovers a novel disconnection approach, harnessing tert-butyl as a potential functional group in strategic synthetic planning for complex molecular architectures.
Collapse
Affiliation(s)
- Siu-Chung Chan
- Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, Girona, E-17071, Catalonia, Spain
| | - Andrea Palone
- Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, Girona, E-17071, Catalonia, Spain
| | - Massimo Bietti
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata"; Via della Ricerca Scientifica, 1, I-00133, Rome, Italy
| | - Miquel Costas
- Institut de Química Computacional i Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, Girona, E-17071, Catalonia, Spain
| |
Collapse
|
2
|
Meger FS, Murphy JA. Recent Advances in C-H Functionalisation through Indirect Hydrogen Atom Transfer. Molecules 2023; 28:6127. [PMID: 37630379 PMCID: PMC10459052 DOI: 10.3390/molecules28166127] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2023] [Revised: 08/09/2023] [Accepted: 08/15/2023] [Indexed: 08/27/2023] Open
Abstract
The functionalisation of C-H bonds has been an enormous achievement in synthetic methodology, enabling new retrosynthetic disconnections and affording simple synthetic equivalents for synthons. Hydrogen atom transfer (HAT) is a key method for forming alkyl radicals from C-H substrates. Classic reactions, including the Barton nitrite ester reaction and Hofmann-Löffler-Freytag reaction, among others, provided early examples of HAT. However, recent developments in photoredox catalysis and electrochemistry have made HAT a powerful synthetic tool capable of introducing a wide range of functional groups into C-H bonds. Moreover, greater mechanistic insights into HAT have stimulated the development of increasingly site-selective protocols. Site-selectivity can be achieved through the tuning of electron density at certain C-H bonds using additives, a judicious choice of HAT reagent, and a solvent system. Herein, we describe the latest methods for functionalizing C-H/Si-H/Ge-H bonds using indirect HAT between 2018-2023, as well as a critical discussion of new HAT reagents, mechanistic aspects, substrate scopes, and background contexts of the protocols.
Collapse
Affiliation(s)
- Filip S. Meger
- Institute of Chemical Research of Catalonia (ICIQ), The Barcelona Institute of Science and Technology, 16 Avinguda dels Països Catalans, 43007 Tarragona, Catalonia, Spain
| | - John A. Murphy
- Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow G1 1XL, UK
| |
Collapse
|
3
|
Chang L, Wang S, An Q, Liu L, Wang H, Li Y, Feng K, Zuo Z. Resurgence and advancement of photochemical hydrogen atom transfer processes in selective alkane functionalizations. Chem Sci 2023; 14:6841-6859. [PMID: 37389263 PMCID: PMC10306100 DOI: 10.1039/d3sc01118f] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 05/11/2023] [Indexed: 07/01/2023] Open
Abstract
The selective functionalization of alkanes has long been recognized as a prominent challenge and an arduous task in organic synthesis. Hydrogen atom transfer (HAT) processes enable the direct generation of reactive alkyl radicals from feedstock alkanes and have been successfully employed in industrial applications such as the methane chlorination process, etc. Nevertheless, challenges in the regulation of radical generation and reaction pathways have created substantial obstacles in the development of diversified alkane functionalizations. In recent years, the application of photoredox catalysis has provided exciting opportunities for alkane C-H functionalization under extremely mild conditions to trigger HAT processes and achieve radical-mediated functionalizations in a more selective manner. Considerable efforts have been devoted to building more efficient and cost-effective photocatalytic systems for sustainable transformations. In this perspective, we highlight the recent development of photocatalytic systems and provide our views on current challenges and future opportunities in this field.
Collapse
Affiliation(s)
- Liang Chang
- School of Pharmacy, Nanjing University of Chinese Medicine Nanjing 210023 China
| | - Shun Wang
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Qing An
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Linxuan Liu
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Hexiang Wang
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Yubo Li
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Kaixuan Feng
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| | - Zhiwei Zuo
- State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences Shanghai 200032 China
| |
Collapse
|
4
|
Ma S, Wang S, Cao J, Liu F. Rapid and Accurate Estimation of Activation Free Energy in Hydrogen Atom Transfer-Based C-H Activation Reactions: From Empirical Model to Artificial Neural Networks. ACS OMEGA 2022; 7:34858-34867. [PMID: 36211072 PMCID: PMC9535641 DOI: 10.1021/acsomega.2c03252] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 09/07/2022] [Indexed: 06/16/2023]
Abstract
A well-performing machine learning (ML) model is obtained by using proper descriptors and artificial neural network (ANN) algorithms, which can quickly and accurately predict activation free energy in hydrogen atom transfer (HAT)-based sp3 C-H activation. Density functional theory calculations (UωB97X-D) are used to establish the reaction system data sets of methoxyl (CH3O·), trifluoroethoxyl (CF3CH2O·), tert-butoxyl (tBuO·), and cumyloxyl (CumO·) radicals. The simplified Roberts' equation proposed in our recent study works here [R 2 = 0.84, mean absolute error (MAE) = 0.85 kcal/mol]. Its performance is comparable with univariate Mulliken-type electronegativity (χ) with the ANN model. The ANN model with bond dissociation free energy, χ, α-unsaturation, and Nolan buried volume (%V buried) successively improves R 2 and MAE to 0.93 and 0.54 kcal/mol, respectively. It reproduces the test sets of trichloroethoxyl (CCl3CH2O·) with R 2 = 0.87 and MAE = 0.89 kcal/mol and accurately predicts the relative experimental barrier of the HAT reactions with CumO· and the site selectivity of CH3O·.
Collapse
Affiliation(s)
- Siqi Ma
- School
of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, Shanghai 201620, China
| | - Shipeng Wang
- School
of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, Shanghai 201620, China
| | - Jiawei Cao
- School
of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, Shanghai 201620, China
| | - Fengjiao Liu
- School
of Chemistry and Chemical Engineering, Shanghai
University of Engineering Science, Shanghai 201620, China
- Department
of Chemistry and Biochemistry, University
of California, Los Angeles, California 90095, United States
| |
Collapse
|
5
|
Galeotti M, Salamone M, Bietti M. Electronic control over site-selectivity in hydrogen atom transfer (HAT) based C(sp 3)-H functionalization promoted by electrophilic reagents. Chem Soc Rev 2022; 51:2171-2223. [PMID: 35229835 DOI: 10.1039/d1cs00556a] [Citation(s) in RCA: 42] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The direct functionalization of C(sp3)-H bonds represents one of the most investigated approaches to develop new synthetic methodology. Among the available strategies for intermolecular C-H bond functionalization, increasing attention has been devoted to hydrogen atom transfer (HAT) based procedures promoted by radical or radical-like reagents, that offer the opportunity to introduce a large variety of atoms and groups in place of hydrogen under mild conditions. Because of the large number of aliphatic C-H bonds displayed by organic molecules, in these processes control over site-selectivity represents a crucial issue, and the associated factors have been discussed. In this review article, attention will be devoted to the role of electronic effects on C(sp3)-H bond functionalization site-selectivity. Through an analysis of the recent literature, a detailed description of the HAT reagents employed in these processes, the associated mechanistic features and the selectivity patterns observed in the functionalization of substrates of increasing structural complexity will be provided.
Collapse
Affiliation(s)
- Marco Galeotti
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica, 1 I-00133 Rome, Italy.
| | - Michela Salamone
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica, 1 I-00133 Rome, Italy.
| | - Massimo Bietti
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica, 1 I-00133 Rome, Italy.
| |
Collapse
|
6
|
Martin T, Galeotti M, Salamone M, Liu F, Yu Y, Duan M, Houk KN, Bietti M. Deciphering Reactivity and Selectivity Patterns in Aliphatic C-H Bond Oxygenation of Cyclopentane and Cyclohexane Derivatives. J Org Chem 2021; 86:9925-9937. [PMID: 34115516 DOI: 10.1021/acs.joc.1c00902] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
A kinetic, product, and computational study on the reactions of the cumyloxyl radical with monosubstituted cyclopentanes and cyclohexanes has been carried out. HAT rates, site-selectivities for C-H bond oxidation, and DFT computations provide quantitative information and theoretical models to explain the observed patterns. Cyclopentanes functionalize predominantly at C-1, and tertiary C-H bond activation barriers decrease on going from methyl- and tert-butylcyclopentane to phenylcyclopentane, in line with the computed C-H BDEs. With cyclohexanes, the relative importance of HAT from C-1 decreases on going from methyl- and phenylcyclohexane to ethyl-, isopropyl-, and tert-butylcyclohexane. Deactivation is also observed at C-2 with site-selectivity that progressively shifts to C-3 and C-4 with increasing substituent steric bulk. The site-selectivities observed in the corresponding oxidations promoted by ethyl(trifluoromethyl)dioxirane support this mechanistic picture. Comparison of these results with those obtained previously for C-H bond azidation and functionalizations promoted by the PINO radical of phenyl and tert-butylcyclohexane, together with new calculations, provides a mechanistic framework for understanding C-H bond functionalization of cycloalkanes. The nature of the HAT reagent, C-H bond strengths, and torsional effects are important determinants of site-selectivity, with the latter effects that play a major role in the reactions of oxygen-centered HAT reagents with monosubstituted cyclohexanes.
Collapse
Affiliation(s)
- Teo Martin
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Marco Galeotti
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Michela Salamone
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Fengjiao Liu
- College of Chemistry and Chemical Engineering, Shanghai University of Engineering Science, Shanghai 201620, China.,Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Yanmin Yu
- Beijing Key Laboratory for Green Catalysis and Separation, Department of Environmental Chemical Engineering, Beijing University of Technology, Beijing 100124, China.,Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Meng Duan
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - K N Houk
- Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States
| | - Massimo Bietti
- Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata", Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| |
Collapse
|
7
|
Capaldo L, Ravelli D, Fagnoni M. Direct Photocatalyzed Hydrogen Atom Transfer (HAT) for Aliphatic C-H Bonds Elaboration. Chem Rev 2021; 122:1875-1924. [PMID: 34355884 PMCID: PMC8796199 DOI: 10.1021/acs.chemrev.1c00263] [Citation(s) in RCA: 305] [Impact Index Per Article: 101.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
![]()
Direct photocatalyzed
hydrogen atom transfer (d-HAT) can be considered
a method of choice for the elaboration of
aliphatic C–H bonds. In this manifold, a photocatalyst (PCHAT) exploits the energy of a photon to trigger the homolytic
cleavage of such bonds in organic compounds. Selective C–H
bond elaboration may be achieved by a judicious choice of the hydrogen
abstractor (key parameters are the electronic character and the molecular
structure), as well as reaction additives. Different are the classes
of PCsHAT available, including aromatic ketones, xanthene
dyes (Eosin Y), polyoxometalates, uranyl salts, a metal-oxo porphyrin
and a tris(amino)cyclopropenium radical dication. The processes (mainly
C–C bond formation) are in most cases carried out under mild
conditions with the help of visible light. The aim of this review
is to offer a comprehensive survey of the synthetic applications of
photocatalyzed d-HAT.
Collapse
Affiliation(s)
- Luca Capaldo
- Flow Chemistry Group, Van't Hoff Institute for Molecular Sciences (HIMS), University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
| | - Davide Ravelli
- PhotoGreen Lab, Department of Chemistry, University of Pavia, Viale Taramelli 12, 27100 Pavia, Italy
| | - Maurizio Fagnoni
- PhotoGreen Lab, Department of Chemistry, University of Pavia, Viale Taramelli 12, 27100 Pavia, Italy
| |
Collapse
|
8
|
Salamone M, Galeotti M, Romero-Montalvo E, van Santen JA, Groff BD, Mayer JM, DiLabio GA, Bietti M. Bimodal Evans-Polanyi Relationships in Hydrogen Atom Transfer from C(sp 3)-H Bonds to the Cumyloxyl Radical. A Combined Time-Resolved Kinetic and Computational Study. J Am Chem Soc 2021; 143:11759-11776. [PMID: 34309387 PMCID: PMC8343544 DOI: 10.1021/jacs.1c05566] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2021] [Indexed: 12/11/2022]
Abstract
The applicability of the Evans-Polanyi (EP) relationship to HAT reactions from C(sp3)-H bonds to the cumyloxyl radical (CumO•) has been investigated. A consistent set of rate constants, kH, for HAT from the C-H bonds of 56 substrates to CumO•, spanning a range of more than 4 orders of magnitude, has been measured under identical experimental conditions. A corresponding set of consistent gas-phase C-H bond dissociation enthalpies (BDEs) spanning 27 kcal mol-1 has been calculated using the (RO)CBS-QB3 method. The log kH' vs C-H BDE plot shows two distinct EP relationships, one for substrates bearing benzylic and allylic C-H bonds (unsaturated group) and the other one, with a steeper slope, for saturated hydrocarbons, alcohols, ethers, diols, amines, and carbamates (saturated group), in line with the bimodal behavior observed previously in theoretical studies of reactions promoted by other HAT reagents. The parallel use of BDFEs instead of BDEs allows the transformation of this correlation into a linear free energy relationship, analyzed within the framework of the Marcus theory. The ΔG⧧HAT vs ΔG°HAT plot shows again distinct behaviors for the two groups. A good fit to the Marcus equation is observed only for the saturated group, with λ = 58 kcal mol-1, indicating that with the unsaturated group λ must increase with increasing driving force. Taken together these results provide a qualitative connection between Bernasconi's principle of nonperfect synchronization and Marcus theory and suggest that the observed bimodal behavior is a general feature in the reactions of oxygen-based HAT reagents with C(sp3)-H donors.
Collapse
Affiliation(s)
- Michela Salamone
- Dipartimento
di Scienze e Tecnologie Chimiche, Università
“Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Marco Galeotti
- Dipartimento
di Scienze e Tecnologie Chimiche, Università
“Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Eduardo Romero-Montalvo
- Department
of Chemistry, The University of British
Columbia, 3247 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - Jeffrey A. van Santen
- Department
of Chemistry, The University of British
Columbia, 3247 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - Benjamin D. Groff
- Department
of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520-8107, United States
| | - James M. Mayer
- Department
of Chemistry, Yale University, 225 Prospect Street, New Haven, Connecticut 06520-8107, United States
| | - Gino A. DiLabio
- Department
of Chemistry, The University of British
Columbia, 3247 University Way, Kelowna, British Columbia, Canada, V1V 1V7
| | - Massimo Bietti
- Dipartimento
di Scienze e Tecnologie Chimiche, Università
“Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| |
Collapse
|
9
|
Vicens L, Olivo G, Costas M. Rational Design of Bioinspired Catalysts for Selective Oxidations. ACS Catal 2020. [DOI: 10.1021/acscatal.0c02073] [Citation(s) in RCA: 62] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Laia Vicens
- Institut de Quı́mica Computacional i Catàlisi (IQCC) and Departament de Quı́mica, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain
| | - Giorgio Olivo
- Institut de Quı́mica Computacional i Catàlisi (IQCC) and Departament de Quı́mica, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain
| | - Miquel Costas
- Institut de Quı́mica Computacional i Catàlisi (IQCC) and Departament de Quı́mica, Universitat de Girona, Campus de Montilivi, 17071 Girona, Spain
| |
Collapse
|
10
|
An Q, Wang Z, Chen Y, Wang X, Zhang K, Pan H, Liu W, Zuo Z. Cerium-Catalyzed C-H Functionalizations of Alkanes Utilizing Alcohols as Hydrogen Atom Transfer Agents. J Am Chem Soc 2020; 142:6216-6226. [PMID: 32181657 DOI: 10.1021/jacs.0c00212] [Citation(s) in RCA: 104] [Impact Index Per Article: 26.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Modern photoredox catalysis has traditionally relied upon metal-to-ligand charge-transfer (MLCT) excitation of metal polypyridyl complexes for the utilization of light energy for the activation of organic substrates. Here, we demonstrate the catalytic application of ligand-to-metal charge-transfer (LMCT) excitation of cerium alkoxide complexes for the facile activation of alkanes utilizing abundant and inexpensive cerium trichloride as the catalyst. As demonstrated by cerium-catalyzed C-H amination and the alkylation of hydrocarbons, this reaction manifold has enabled the facile use of abundant alcohols as practical and selective hydrogen atom transfer (HAT) agents via the direct access of energetically challenging alkoxy radicals. Furthermore, the LMCT excitation event has been investigated through a series of spectroscopic experiments, revealing a rapid bond homolysis process and an effective production of alkoxy radicals, collectively ruling out the LMCT/homolysis event as the rate-determining step of this C-H functionalization.
Collapse
Affiliation(s)
- Qing An
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,University of Chinese Academy of Science, Shanghai 100049, China
| | - Ziyu Wang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,University of Chinese Academy of Science, Shanghai 100049, China
| | - Yuegang Chen
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
| | - Xin Wang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,University of Chinese Academy of Science, Shanghai 100049, China
| | - Kaining Zhang
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,University of Chinese Academy of Science, Shanghai 100049, China
| | - Hui Pan
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,University of Chinese Academy of Science, Shanghai 100049, China
| | - Weimin Liu
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,STU & SIOM Joint Laboratory for Superintense Lasers and the Applications, Shanghai 201210, China
| | - Zhiwei Zuo
- School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.,State Key Laboratory of Bioorganic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China
| |
Collapse
|
11
|
Dirhodium tetracarboxylates as catalysts for selective intermolecular C-H functionalization. Nat Rev Chem 2019; 3:347-360. [PMID: 32995499 DOI: 10.1038/s41570-019-0099-x] [Citation(s) in RCA: 190] [Impact Index Per Article: 38.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
C-H Functionalization has become widely recognized as an exciting new strategy for the synthesis of complex molecular targets. Instead of relying on functional groups as the controlling elements of how molecules are assembled, it offers a totally different logic for organic synthesis. For this type of strategy to be successful, reagents and catalysts need to be developed that generate intermediates that are sufficiently reactive to functionalize C-H bonds but still capable of distinguishing between the different C-H bonds and other functional groups present in a molecule. The most well-established approaches have tended to use substrates that have inherently a favored site for C-H functionalization or rely on intramolecular reactions to control where the reaction will occur. A challenging but potentially more versatile approach would be to use catalysts to control the site-selectivity without requiring the influence of any directing group. One example that is capable of achieving such transformations is the C-H insertion chemistry of transient metal carbenes. Dirhodium tetracarboxylates have been shown to be especially effective catalysts for these reactions. This review will highlight the development of these dirhodium catalysts and illustrate their effectiveness to control both site-selective and stereoselective C-H functionalization of a wide variety of substrates.
Collapse
|
12
|
Milan M, Salamone M, Costas M, Bietti M. The Quest for Selectivity in Hydrogen Atom Transfer Based Aliphatic C-H Bond Oxygenation. Acc Chem Res 2018; 51:1984-1995. [PMID: 30080039 DOI: 10.1021/acs.accounts.8b00231] [Citation(s) in RCA: 94] [Impact Index Per Article: 15.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Aliphatic C-H bond functionalization is at the frontline of research because it can provide straightforward access to simplified and cost-effective synthetic procedures. A number of these methodologies are based on hydrogen atom transfer (HAT), which, as a consequence of the inert character of C-H bonds, often represents the most challenging step of the overall process. Because the majority of organic molecules contain multiple nonequivalent C-H bonds that display similar chemical properties, differentiating between these bonds with high levels of selectivity represents one of the most challenging issues. Clarification of the factors that govern the relative reactivity of C-H bonds toward HAT reagents is thus of primary importance in order to develop selective functionalization procedures. In this Account we describe, through the combination of kinetic studies employing a genuine HAT reagent such as the cumyloxyl radical, along with oxidations performed with H2O2 and iron or manganese catalysts, our contribution toward the development of selective C-H functionalization methodologies. Despite the different nature of these reagents, an oxygen-centered radical and a metal-oxo species, congruent reactivity and selectivity patterns have emerged, providing strong evidence that both reactions proceed via HAT. Consequently, selectivity in this class of metal catalyzed C-H oxidations can be reasonably predicted and synthetically exploited. Amides have been identified as preferential functional groups for governing selectivity on the basis of electronic, steric, and stereoelectronic effects. Torsional effects have proven moreover to be particularly important C-H directing factors in the oxidation of cyclohexane scaffolds where a delicate balance of these effects, in synergistic combination with catalyst design, enables highly chemoselective and enantioselective oxidations. Medium effects have been also shown to govern the relative HAT reactivity of C-H bonds in proximity to polar, hydrogen bond acceptor (HBA) functional groups. By engaging in hydrogen bonding with these groups, fluorinated alcohols strongly deactivate proximal C-H bonds toward HAT-based oxidation. As a result, alcohols, ethers, amines, and amides, which are electron rich and effective proximal C-H activating groups toward HAT reagents in conventional solvents, become oxidatively robust deactivating functionalities that direct C-H oxidation toward remote positions. These deactivating effects enable moreover the accomplishment of product chemoselective methylenic hydroxylations. Overall, clarification of the factors that govern HAT-based reactions has served to provide unique examples of catalytic methodologies for chemoselective and enantioselective oxidation of nonactivated aliphatic C-H bonds of potential utility in organic synthesis.
Collapse
Affiliation(s)
- Michela Milan
- QBIS Research Group, Institut de Química Computacional i Catàlisi (IQCC), and Departament de Química, Universitat de Girona, Campus Montilivi, Girona, E-17071 Catalonia, Spain
| | - Michela Salamone
- Dipartimento di Scienze e Tecnologie Chimiche, Università “Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Miquel Costas
- QBIS Research Group, Institut de Química Computacional i Catàlisi (IQCC), and Departament de Química, Universitat de Girona, Campus Montilivi, Girona, E-17071 Catalonia, Spain
| | - Massimo Bietti
- Dipartimento di Scienze e Tecnologie Chimiche, Università “Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| |
Collapse
|
13
|
Wang Y, Hu X, Morales-Rivera CA, Li GX, Huang X, He G, Liu P, Chen G. Epimerization of Tertiary Carbon Centers via Reversible Radical Cleavage of Unactivated C(sp 3)-H Bonds. J Am Chem Soc 2018; 140:9678-9684. [PMID: 29983059 DOI: 10.1021/jacs.8b05753] [Citation(s) in RCA: 41] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Reversible cleavage of C(sp3)-H bonds can enable racemization or epimerization, offering a valuable tool to edit the stereochemistry of organic compounds. While epimerization reactions operating via cleavage of acidic C(sp3)-H bonds, such as the Cα-H of carbonyl compounds, have been widely used in organic synthesis and enzyme-catalyzed biosynthesis, epimerization of tertiary carbons bearing a nonacidic C(sp3)-H bond is much more challenging with few practical methods available. Herein, we report the first synthetically useful protocol for the epimerization of tertiary carbons via reversible radical cleavage of unactivated C(sp3)-H bonds with hypervalent iodine reagent benziodoxole azide and H2O under mild conditions. These reactions exhibit excellent reactivity and selectivity for unactivated 3° C-H bonds of various cycloalkanes and offer a powerful strategy for editing the stereochemical configurations of carbon scaffolds intractable to conventional methods. Mechanistic study suggests that the unique ability of N3• to serve as a catalytic H atom shuttle is critical to reversibly break and reform 3° C-H bonds with high efficiency and selectivity.
Collapse
Affiliation(s)
- Yaxin Wang
- State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China
| | - Xiafei Hu
- State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China
| | - Cristian A Morales-Rivera
- Department of Chemistry , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States
| | - Guo-Xing Li
- State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China
| | - Xin Huang
- State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China
| | - Gang He
- State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China.,Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) , Tianjin 300071 , China
| | - Peng Liu
- Department of Chemistry , University of Pittsburgh , Pittsburgh , Pennsylvania 15260 , United States
| | - Gong Chen
- State Key Laboratory and Institute of Elemento-Organic Chemistry, College of Chemistry , Nankai University , Tianjin 300071 , China.,Collaborative Innovation Center of Chemical Science and Engineering (Tianjin) , Tianjin 300071 , China.,Department of Chemistry , The Pennsylvania State University , University Park , Pennsylvania 16802 , United States
| |
Collapse
|
14
|
Milan M, Bietti M, Costas M. Aliphatic C-H Bond Oxidation with Hydrogen Peroxide Catalyzed by Manganese Complexes: Directing Selectivity through Torsional Effects. Org Lett 2018; 20:2720-2723. [PMID: 29676920 DOI: 10.1021/acs.orglett.8b00929] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Substituted N-cyclohexyl amides undergo aliphatic C-H bond oxidation with H2O2 catalyzed by manganese complexes. The reactions are directed by torsional effects leading to site-selective oxidation of cis-1,4-, trans-1,3-, and cis-1,2-cyclohexanediamides. The corresponding diastereoisomers are unreactive under the same conditions. Competitive oxidation of cis- trans mixtures of 4-substituted N-cyclohexylamides leads to quantitative conversion of the cis-isomers, allowing isolation and successive conversion of the trans-isomers into densely functionalized oxidation products with excellent site selectivity and good enantioselectivity.
Collapse
Affiliation(s)
- Michela Milan
- Institut de Química Computational i Catàlisi, IQCC and Departament de Química , Universitat de Girona , Campus de Montilivi , 17003 Girona , Spain
| | - Massimo Bietti
- Dipartimento di Scienze e Tecnologie Chimiche , Università"Tor Vergata" , Via della Ricerca Scientifica, 1 , I-00133 Rome , Italy
| | - Miquel Costas
- Institut de Química Computational i Catàlisi, IQCC and Departament de Química , Universitat de Girona , Campus de Montilivi , 17003 Girona , Spain
| |
Collapse
|
15
|
Salamone M, Ortega VB, Martin T, Bietti M. Hydrogen Atom Transfer from Alkanols and Alkanediols to the Cumyloxyl Radical: Kinetic Evaluation of the Contribution of α-C-H Activation and β-C-H Deactivation. J Org Chem 2018; 83:5539-5545. [PMID: 29668277 DOI: 10.1021/acs.joc.8b00562] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
A kinetic study on the reactions of the cumyloxyl radical (CumO•) with a series of alkanols and alkanediols has been carried out. Predominant hydrogen atom transfer (HAT) from the α-C-H bonds of these substrates, activated by the presence of the OH group, is observed. The comparable kH values measured for ethanol and 1-propanol and the increase in kH measured upon going from 1,2-diols to structurally related 1,3- and 1,4-diols is indicative of β-C-H deactivation toward HAT to the electrophilic CumO•, determined by the electron-withdrawing character of the OH group. No analogous deactivation is observed for the corresponding diamines, in agreement with the weaker electron-withdrawing character of the NH2 group. The significantly lower kH values measured for reaction of CumO• with densely oxygenated methyl pyranosides as compared to cyclohexanol derivatives highlights the role of β-C-H deactivation. The contribution of torsional effects on reactivity is evidenced by the ∼2-fold increase in kH observed upon going from the trans isomers of 4- tert-butylcyclohexanol and 1,2- and 1,4-cyclohexanediol to the corresponding cis isomers. These results provide an evaluation of the role of electronic and torsional effects on HAT reactions from alcohols and diols to CumO•, uncovering moreover β-C-H deactivation as a relevant contributor in defining site selectivity.
Collapse
Affiliation(s)
- Michela Salamone
- Dipartimento di Scienze e Tecnologie Chimiche , Università "Tor Vergata" , Via della Ricerca Scientifica 1 , I-00133 Rome , Italy
| | - Vanesa B Ortega
- Dipartimento di Scienze e Tecnologie Chimiche , Università "Tor Vergata" , Via della Ricerca Scientifica 1 , I-00133 Rome , Italy
| | - Teo Martin
- Dipartimento di Scienze e Tecnologie Chimiche , Università "Tor Vergata" , Via della Ricerca Scientifica 1 , I-00133 Rome , Italy
| | - Massimo Bietti
- Dipartimento di Scienze e Tecnologie Chimiche , Università "Tor Vergata" , Via della Ricerca Scientifica 1 , I-00133 Rome , Italy
| |
Collapse
|
16
|
Kim KE, Adams AM, Chiappini ND, Du Bois J, Stoltz BM. Cyanthiwigin Natural Product Core as a Complex Molecular Scaffold for Comparative Late-Stage C–H Functionalization Studies. J Org Chem 2018; 83:3023-3033. [DOI: 10.1021/acs.joc.7b03291] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Kelly E. Kim
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| | - Ashley M. Adams
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Nicholas D. Chiappini
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - J. Du Bois
- Department of Chemistry, Stanford University, Stanford, California 94305, United States
| | - Brian M. Stoltz
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States
| |
Collapse
|
17
|
Dantignana V, Milan M, Cussó O, Company A, Bietti M, Costas M. Chemoselective Aliphatic C-H Bond Oxidation Enabled by Polarity Reversal. ACS CENTRAL SCIENCE 2017; 3:1350-1358. [PMID: 29296677 PMCID: PMC5746866 DOI: 10.1021/acscentsci.7b00532] [Citation(s) in RCA: 92] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/05/2017] [Indexed: 06/07/2023]
Abstract
Methods for selective oxidation of aliphatic C-H bonds are called on to revolutionize organic synthesis by providing novel and more efficient paths. Realization of this goal requires the discovery of mechanisms that can alter in a predictable manner the innate reactivity of these bonds. Ideally, these mechanisms need to make oxidation of aliphatic C-H bonds, which are recognized as relatively inert, compatible with the presence of electron rich functional groups that are highly susceptible to oxidation. Furthermore, predictable modification of the relative reactivity of different C-H bonds within a molecule would enable rapid diversification of the resulting oxidation products. Herein we show that by engaging in hydrogen bonding, fluorinated alcohols exert a polarity reversal on electron rich functional groups, directing iron and manganese catalyzed oxidation toward a priori stronger and unactivated C-H bonds. As a result, selective hydroxylation of methylenic sites in hydrocarbons and remote aliphatic C-H oxidation of otherwise sensitive alcohol, ether, amide, and amine substrates is achieved employing aqueous hydrogen peroxide as oxidant. Oxidations occur in a predictable manner, with outstanding levels of product chemoselectivity, preserving the first-formed hydroxylation product, thus representing an extremely valuable tool for synthetic planning and development.
Collapse
Affiliation(s)
- Valeria Dantignana
- Grup
de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT),
Institut de Química Computacional i Catàlisi (IQCC)
and Departament de Química, Universitat
de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
| | - Michela Milan
- Grup
de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT),
Institut de Química Computacional i Catàlisi (IQCC)
and Departament de Química, Universitat
de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
| | - Olaf Cussó
- Grup
de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT),
Institut de Química Computacional i Catàlisi (IQCC)
and Departament de Química, Universitat
de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
| | - Anna Company
- Grup
de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT),
Institut de Química Computacional i Catàlisi (IQCC)
and Departament de Química, Universitat
de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
| | - Massimo Bietti
- Dipartimento
di Scienze e Tecnologie Chimiche, Università
“Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Miquel Costas
- Grup
de Química Bioinspirada, Supramolecular i Catàlisi (QBIS-CAT),
Institut de Química Computacional i Catàlisi (IQCC)
and Departament de Química, Universitat
de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
| |
Collapse
|
18
|
Salamone M, Martin T, Milan M, Costas M, Bietti M. Electronic and Torsional Effects on Hydrogen Atom Transfer from Aliphatic C–H Bonds: A Kinetic Evaluation via Reaction with the Cumyloxyl Radical. J Org Chem 2017; 82:13542-13549. [DOI: 10.1021/acs.joc.7b02654] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Michela Salamone
- Dipartimento
di Scienze e Tecnologie Chimiche, Università “Tor Vergata”, Via della Ricerca Scientifica, 1 I-00133 Rome, Italy
| | - Teo Martin
- Dipartimento
di Scienze e Tecnologie Chimiche, Università “Tor Vergata”, Via della Ricerca Scientifica, 1 I-00133 Rome, Italy
| | - Michela Milan
- QBIS
Research Group, Institut de Química Computacional i Catàlisi
(IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
| | - Miquel Costas
- QBIS
Research Group, Institut de Química Computacional i Catàlisi
(IQCC) and Departament de Química, Universitat de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
| | - Massimo Bietti
- Dipartimento
di Scienze e Tecnologie Chimiche, Università “Tor Vergata”, Via della Ricerca Scientifica, 1 I-00133 Rome, Italy
| |
Collapse
|
19
|
Milan M, Bietti M, Costas M. Highly Enantioselective Oxidation of Nonactivated Aliphatic C-H Bonds with Hydrogen Peroxide Catalyzed by Manganese Complexes. ACS CENTRAL SCIENCE 2017; 3:196-204. [PMID: 28386597 PMCID: PMC5364455 DOI: 10.1021/acscentsci.6b00368] [Citation(s) in RCA: 129] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Indexed: 05/21/2023]
Abstract
Monosubstituted cycloalkanes undergo regio- and enantioselective aliphatic C-H oxidation with H2O2 catalyzed by biologically inspired manganese catalysts. The reaction furnishes the corresponding ketones resulting from oxidation at C3 and C4 methylenic sites (K3 and K4, respectively) leading to a chiral desymmetrization that proceeds with remarkable enantioselectivity (64% ee) but modest regioselectivity at C3 (K3/K4 ≈ 2) for tert-butylcyclohexane, and with up to 96% ee and exquisite regioselectity toward C3 (up to K3/K4 > 99) when N-cyclohexylalkanamides are employed as substrates. Efficient H2O2 activation, high yield, and highly enantioselective C-H oxidation rely on the synergistic cooperation of a sterically bulky manganese catalyst and an oxidatively robust alkanoic acid. This represents the first example of nonenzymatic highly enantioselective oxidation of nonactivated methylenic sites. Furthermore, the principles of catalyst design disclosed in this work constitute a unique platform for further development of stereoselective C-H oxidation reactions.
Collapse
Affiliation(s)
- Michela Milan
- QBIS Research Group,
Institut de Química Computacional i Catàlisi (IQCC)
and Departament de Química, Universitat
de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
| | - Massimo Bietti
- Dipartimento di
Scienze e Tecnologie Chimiche, Università
“Tor Vergata”, Via della Ricerca Scientifica, 1, I-00133 Rome, Italy
- (M.B.) E-mail:
| | - Miquel Costas
- QBIS Research Group,
Institut de Química Computacional i Catàlisi (IQCC)
and Departament de Química, Universitat
de Girona, Campus Montilivi, Girona E-17071, Catalonia, Spain
- (M.C.) Tel: +34-972419842. E-mail:
| |
Collapse
|
20
|
Olivo G, Cussó O, Costas M. Biologically Inspired C−H and C=C Oxidations with Hydrogen Peroxide Catalyzed by Iron Coordination Complexes. Chem Asian J 2016; 11:3148-3158. [DOI: 10.1002/asia.201601170] [Citation(s) in RCA: 67] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2016] [Revised: 09/26/2016] [Indexed: 11/05/2022]
Affiliation(s)
- Giorgio Olivo
- Departament de Química I Institut de Química Computacional i Catàlisi (IQCC); Universitat de Girona; Facultat de Ciències, Campus de Montilivi; Girona 17071 Spain
| | - Olaf Cussó
- Departament de Química I Institut de Química Computacional i Catàlisi (IQCC); Universitat de Girona; Facultat de Ciències, Campus de Montilivi; Girona 17071 Spain
| | - Miquel Costas
- Departament de Química I Institut de Química Computacional i Catàlisi (IQCC); Universitat de Girona; Facultat de Ciències, Campus de Montilivi; Girona 17071 Spain
| |
Collapse
|
21
|
Font D, Canta M, Milan M, Cussó O, Ribas X, Klein Gebbink RJM, Costas M. Readily Accessible Bulky Iron Catalysts exhibiting Site Selectivity in the Oxidation of Steroidal Substrates. Angew Chem Int Ed Engl 2016; 55:5776-9. [PMID: 27059402 DOI: 10.1002/anie.201600785] [Citation(s) in RCA: 76] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Indexed: 11/07/2022]
Abstract
Bulky iron complexes are described that catalyze the site-selective oxidation of alkyl C-H bonds with hydrogen peroxide under mild conditions. Steric bulk at the iron center is introduced by appending trialkylsilyl groups at the meta-position of the pyridines in tetradentate aminopyridine ligands, and this effect translates into high product yields, an enhanced preferential oxidation of secondary over tertiary C-H bonds, and the ability to perform site-selective oxidation of methylenic sites in terpenoid and steroidal substrates. Unprecedented site selective oxidation at C6 and C12 methylenic sites in steroidal substrates is shown to be governed by the chirality of the catalysts.
Collapse
Affiliation(s)
- David Font
- Institut de Química Computacional I Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, 17071, Girona, Catalonia, Spain
| | - Mercè Canta
- Institut de Química Computacional I Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, 17071, Girona, Catalonia, Spain
| | - Michela Milan
- Institut de Química Computacional I Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, 17071, Girona, Catalonia, Spain
| | - Olaf Cussó
- Institut de Química Computacional I Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, 17071, Girona, Catalonia, Spain
| | - Xavi Ribas
- Institut de Química Computacional I Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, 17071, Girona, Catalonia, Spain
| | - Robertus J M Klein Gebbink
- Organic Chemistry & Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Universiteitsweg 99, 3584, CG Utrecht, The Netherlands.
| | - Miquel Costas
- Institut de Química Computacional I Catàlisi (IQCC), Departament de Química, Universitat de Girona, Campus Montilivi, 17071, Girona, Catalonia, Spain.
| |
Collapse
|
22
|
Font D, Canta M, Milan M, Cussó O, Ribas X, Klein Gebbink RJM, Costas M. Readily Accessible Bulky Iron Catalysts exhibiting Site Selectivity in the Oxidation of Steroidal Substrates. Angew Chem Int Ed Engl 2016. [DOI: 10.1002/ange.201600785] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Affiliation(s)
- David Font
- Institut de Química Computacional I Catàlisi (IQCC); Departament de Química; Universitat de Girona; Campus Montilivi 17071 Girona Catalonia, Spain
| | - Mercè Canta
- Institut de Química Computacional I Catàlisi (IQCC); Departament de Química; Universitat de Girona; Campus Montilivi 17071 Girona Catalonia, Spain
| | - Michela Milan
- Institut de Química Computacional I Catàlisi (IQCC); Departament de Química; Universitat de Girona; Campus Montilivi 17071 Girona Catalonia, Spain
| | - Olaf Cussó
- Institut de Química Computacional I Catàlisi (IQCC); Departament de Química; Universitat de Girona; Campus Montilivi 17071 Girona Catalonia, Spain
| | - Xavi Ribas
- Institut de Química Computacional I Catàlisi (IQCC); Departament de Química; Universitat de Girona; Campus Montilivi 17071 Girona Catalonia, Spain
| | - Robertus J. M. Klein Gebbink
- Organic Chemistry & Catalysis; Debye Institute for Nanomaterials Science; Utrecht University; Universiteitsweg 99 3584 CG Utrecht The Netherlands
| | - Miquel Costas
- Institut de Química Computacional I Catàlisi (IQCC); Departament de Química; Universitat de Girona; Campus Montilivi 17071 Girona Catalonia, Spain
| |
Collapse
|
23
|
Salamone M, Bietti M. Tuning reactivity and selectivity in hydrogen atom transfer from aliphatic C-H bonds to alkoxyl radicals: role of structural and medium effects. Acc Chem Res 2015; 48:2895-903. [PMID: 26545103 DOI: 10.1021/acs.accounts.5b00348] [Citation(s) in RCA: 155] [Impact Index Per Article: 17.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Hydrogen atom transfer (HAT) is a fundamental reaction that takes part in a wide variety of chemical and biological processes, with relevant examples that include the action of antioxidants, damage to biomolecules and polymers, and enzymatic and biomimetic reactions. Moreover, great attention is currently devoted to the selective functionalization of unactivated aliphatic C-H bonds, where HAT based procedures have been shown to play an important role. In this Account, we describe the results of our recent studies on the role of structural and medium effects on HAT from aliphatic C-H bonds to the cumyloxyl radical (CumO(•)). Quantitative information on the reactivity and selectivity patterns observed in these reactions has been obtained by time-resolved kinetic studies, providing a deeper understanding of the factors that govern HAT from carbon and leading to the definition of useful guidelines for the activation or deactivation of aliphatic C-H bonds toward HAT. In keeping with the electrophilic character of alkoxyl radicals, polar effects can play an important role in the reactions of CumO(•). Electron-rich C-H bonds are activated whereas those that are α to electron withdrawing groups are deactivated toward HAT, with these effects being able to override the thermodynamic preference for HAT from the weakest C-H bond. Stereoelectronic effects can also influence the reactivity of the C-H bonds of ethers, amines, and amides. HAT is most rapid when these bonds can be eclipsed with a lone pair on an adjacent heteroatom or with the π-system of an amide functionality, thus allowing for optimal orbital overlap. In HAT from cyclohexane derivatives, tertiary axial C-H bond deactivation and tertiary equatorial C-H bond activation have been observed. These effects have been explained on the basis of an increase in torsional strain or a release in 1,3-diaxial strain in the HAT transition states, with kH(eq)/kH(ax) ratios that have been shown to exceed one order of magnitude. Medium effects on HAT from aliphatic C-H bonds to CumO(•) have been also investigated. With basic substrates, from large to very large decreases in kH have been measured with increasing solvent hydrogen bond donor (HBD) ability or after addition of protic acids or alkali and alkaline earth metal ions, with kinetic effects that exceed 2 orders of magnitude in the reactions of tertiary alkylamines and alkanamides. Solvent hydrogen bonding, protonation, and metal ion binding increase the electron deficiency and the strength of the C-H bonds of these substrates deactivating these bonds toward HAT, with the extent of this deactivation being modulated by varying the nature of the substrate, solvent, protic acid, and metal ion. These results indicate that through these interactions careful control over the HAT reactivity of basic substrates toward CumO(•) and other electrophilic radicals can be achieved, suggesting moreover that these effects can be exploited in an orthogonal fashion for selective C-H bond functionalization of substrates bearing different basic functionalities.
Collapse
Affiliation(s)
- Michela Salamone
- Dipartimento
di Scienze e
Tecnologie Chimiche, Università “Tor Vergata”, Via
della Ricerca Scientifica, 1, I-00133 Rome, Italy
| | - Massimo Bietti
- Dipartimento
di Scienze e
Tecnologie Chimiche, Università “Tor Vergata”, Via
della Ricerca Scientifica, 1, I-00133 Rome, Italy
| |
Collapse
|