1
|
Control of Selectivity in FeCl 3 -Catalyzed Aerobic Oxidation of Cycloketones. Chem Asian J 2023; 18:e202201101. [PMID: 36519526 DOI: 10.1002/asia.202201101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 12/12/2022] [Accepted: 12/12/2022] [Indexed: 12/23/2022]
Abstract
The FeCl3 -catalyzed aerobic oxidation of ketones always gives rise to the α-C-C cleavage product, having challenges to afford hydroxyl keto compounds. Here we report an effective control of the main product from keto acid to α-hydroxyl ketone, by reducing the concentration of FeCl3 catalyst, together with the use of DMSO as the solvent. In addition, mechanistic investigations suggested the same FeCl3 -coordinated peroxide intermediate for both hydroxylation and C-C cleavage routes, and emphasize the role of DMSO as both ligand and reductant. This work provides a new approach for selective aerobic oxidation under Lewis acid catalysis.
Collapse
|
2
|
Precisely Tailoring Heterometallic Polyoxotitanium Clusters for the Efficient and Selective Photocatalytic Oxidation of Hydrocarbons. Angew Chem Int Ed Engl 2022; 61:e202215540. [PMID: 36314983 DOI: 10.1002/anie.202215540] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2022] [Indexed: 11/05/2022]
Abstract
Photocatalysis is a promising yet challenging approach for the selective oxidation of hydrocarbons to valuable oxygenated chemicals with O2 under mild conditions. In this work, we report an atomically precise material model to address this challenge. The key to our solution is the rational incorporation of Fe species into polyoxotitanium cluster to form a heterometallic Ti4 Fe1 cocrystal. This newly designed cocrystal cluster, which well governs the energy and charge transfer as evidenced by spectroscopic characterizations and theoretical calculations, enables the synergistic process involving C(sp3 )-H bond activation by photogenerated holes and further reactions by singlet oxygen (1 O2 ). Remarkably, the cocrystal Ti4 Fe1 cluster achieves efficient and selective oxidation of hydrocarbons (C5 to C16 ) into aldehydes and ketones with a conversion rate up to 12 860 μmol g-1 h-1 , 5 times higher than that of Fe-doped Ti3 Fe1 cluster. This work provides insights into photocatalyst design at atomic level enabling synergistic catalysis.
Collapse
|
3
|
Pd-catalyzed Aerobic Cross-Dehydrogenative Coupling of Catechols with 2-Oxindoles and Benzofuranones: Reactivity Difference Between Monomer and Dimer. Chem Asian J 2022; 17:e202200807. [PMID: 36062560 PMCID: PMC9825984 DOI: 10.1002/asia.202200807] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/02/2022] [Revised: 09/05/2022] [Indexed: 01/11/2023]
Abstract
Persistent radicals, which are generated from 2-oxindole or benzofuranone dimers, are useful tools for designing the radical-based cross-coupling reaction to provide molecules containing a quaternary carbon. The persistent radical is accessible from both the dimer and monomer; however, the reactivity difference between these substrates for the oxidative cross-coupling reaction is not fully understood, most likely because of the mechanistic complexity. Here, we present details of an aerobic cross-dehydrogenative coupling (CDC) reaction using various monomers and catechols. UV-Vis analysis and mechanistic control experiments showed that the monomer is less reactive than the dimer under aerobic conditions. Our Pd(II)-BINAP-μ-hydroxo complex significantly improved the reactivity of the monomers for the aerobic CDC reaction with catechols, yielding results comparable to those of the corresponding dimer. The procedure, which enables the generation of the persistent radical in situ, is particularly useful when employing the monomer that is not readily converted to the corresponding dimer.
Collapse
|
4
|
Inorganic Bases Enhanced Organocatalysis for Aerobic αHydroxylation of Aliphatic Cycloketones. ASIAN J ORG CHEM 2022. [DOI: 10.1002/ajoc.202200443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
5
|
In-Situ Anchoring Pb-Free Cs 3 Bi 2 Br 9 @BiOBr Quantum Dots on NH x -Rich Silica with Enhanced Blue Emission and Satisfactory Stability for Photocatalytic Toluene Oxidation. CHEMSUSCHEM 2022; 15:e202200793. [PMID: 35674682 DOI: 10.1002/cssc.202200793] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Revised: 05/24/2022] [Indexed: 06/15/2023]
Abstract
All-inorganic metal halide perovskite quantum dots (QDs) have attracted attention from researchers with their fascinating optoelectronic properties. However, blue-emitting perovskite QDs typically have low photoluminescence quantum yield (PLQY). For potential commercial applications, it is preferable to replace Pb with an element having low toxicity. Here, Pb-free Cs3 Bi2 Br9 @BiOBr perovskite QDs were anchored on the surface of NHx -rich monodisperse silica (A-SiO2 ) via N-Bi chemical bonding to isolate QDs from each other, thus enhancing efficient surface passivation and suppressing optical decay. Compared to unanchored QDs, Cs3 Bi2 Br9 @BiOBr QDs/A-SiO2 composites exhibited significantly enhanced blue emission performance, the PLQY of which increased from 16.62 % to 77.26 %, in addition to good water and environmental stability. Finally, the novel composites as photocatalysts were used to drive the oxidation of toluene, a template reaction of C(sp3 )-H bond activation and demonstrated astonishing conversion rates (4317 μmol g-1 h-1 ) with high selectivity (around 87 %).
Collapse
|
6
|
Chemoselective Oxyfunctionalization of Functionalized Benzylic Compounds with a Manganese Catalyst. Angew Chem Int Ed Engl 2022; 61:e202205983. [PMID: 35594169 PMCID: PMC9400980 DOI: 10.1002/anie.202205983] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Indexed: 11/06/2022]
Abstract
Whilst allowing for easy access to synthetically versatile motifs and for modification of bioactive molecules, the chemoselective benzylic oxidation reactions of functionalized alkyl arenes remain challenging. Reported in this study is a new non‐heme Mn catalyst stabilized by a bipiperidine‐based tetradentate ligand, which enables methylene oxidation of benzylic compounds by H2O2, showing high activity and excellent chemoselectivity under mild conditions. The protocol tolerates an unprecedentedly wide range of functional groups, including carboxylic acid and derivatives, ketone, cyano, azide, acetate, sulfonate, alkyne, amino acid, and amine units, thus providing a low‐cost, more sustainable and robust pathway for the facile synthesis of ketones, increase of complexity of organic molecules, and late‐stage modification of drugs.
Collapse
|
7
|
Electrosynthesis of ortho‐Amino Aryl Ketones by Aerobic Electrooxidative Cleavage of the C(2)=C(3)/C(2)‐N Bonds of N‐Boc Indoles. Adv Synth Catal 2022. [DOI: 10.1002/adsc.202200256] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
|
8
|
Photogenerated Azido Radical Mediated Oxidation: Access to Carbonyl Functionality from Alcohols, Alkylarenes, and Olefins via Organophotoredox. Adv Synth Catal 2022. [DOI: 10.1002/adsc.202200242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
9
|
Chemoselective Oxyfunctionalization of Functionalized Benzylic Compounds with a Manganese Catalyst. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202205983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
10
|
Cu
2
O‐CuO/Chitosan Composites as Heterogeneous Catalysts for Benzylic C−H Oxidation at Room Temperature. ChemCatChem 2021. [DOI: 10.1002/cctc.202101187] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
11
|
Molecular Triad Containing a TEMPO Catalyst Grafted on Mesoporous Indium Tin Oxide as a Photoelectrocatalytic Anode for Visible Light-Driven Alcohol Oxidation. CHEMSUSCHEM 2021; 14:2902-2913. [PMID: 33973386 DOI: 10.1002/cssc.202100843] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/22/2021] [Revised: 05/05/2021] [Indexed: 06/12/2023]
Abstract
Photoelectrochemical cells based on semiconductors are among the most studied methods of artificial photosynthesis. This study concerns the immobilization, on a mesoporous conducting indium tin oxide electrode (nano-ITO), of a molecular triad (NDADI-P-Ru-TEMPO) composed of a ruthenium tris-bipyridine complex (Ru) as photosensitizer, connected at one end to 2,2,6,6-tetramethyl-1-piperidine N-oxyl (TEMPO) as alcohol oxidation catalyst and at the other end to the electron acceptor naphthalenedicarboxyanhydride dicarboximide (NDADI). Light irradiation of NDADI-P-Ru-TEMPO grafted to nano-ITO in a pH 10 carbonate buffer effects selective oxidation of para-methoxybenzyl alcohol (MeO-BA) to para-methoxybenzaldehyde with a TON of approximately 150 after 1 h of photolysis at a bias of 0.4 V vs. SCE. The faradaic efficiency is found to be of 80±5 %. The photophysical study indicates that photoinduced electron transfer from the Ru complex to NDADI is a slow process and must compete with direct electron injection into ITO to have a better performing system. This work sheds light on some of the important ways to design more efficient molecular systems for the preparation of photoelectrocatalytic cells based on catalyst-dye-acceptor arrays immobilized on conducting electrodes.
Collapse
|
12
|
Efficient Aerobic Oxidation of Organic Molecules by Multistep Electron Transfer. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202012707] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
|
13
|
Efficient Aerobic Oxidation of Organic Molecules by Multistep Electron Transfer. Angew Chem Int Ed Engl 2021; 60:15686-15704. [PMID: 33368909 PMCID: PMC9545650 DOI: 10.1002/anie.202012707] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Indexed: 12/17/2022]
Abstract
This Minireview presents recent important homogenous aerobic oxidative reactions which are assisted by electron transfer mediators (ETMs). Compared with direct oxidation by molecular oxygen (O2), the use of a coupled catalyst system with ETMs leads to a lower overall energy barrier via stepwise electron transfer. This cooperative catalytic process significantly facilitates the transport of electrons from the reduced form of the substrate‐selective redox catalyst (SSRCred) to O2, thereby increasing the efficiency of the aerobic oxidation. In this Minireview, we have summarized the advances accomplished in recent years in transition‐metal‐catalyzed as well as metal‐free aerobic oxidations of organic molecules in the presence of ETMs. In addition, the recent progress of photochemical and electrochemical oxidative functionalization using ETMs and O2 as the terminal oxidant is also highlighted. Furthermore, the mechanisms of these transformations are showcased.
Collapse
|
14
|
Transition Metal-Catalyzed C-H Oxidation of Saturated Hydrocarbons with Molecular Oxygen. CHEM REC 2021; 21:1928-1940. [PMID: 34235852 DOI: 10.1002/tcr.202100154] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2021] [Revised: 06/22/2021] [Indexed: 01/22/2023]
Abstract
The C-H oxidation of saturated hydrocarbons to the corresponding alcohols and ketones can be performed efficiently at room temperature with molecular oxygen (1 atm) in the presence of acetaldehyde and catalysts such as Fe, Cu(OH)2 , and CuCl2 -18-crown-6 complex. Moreover, extremely high turnover numbers (>27,000) have been obtained for the C-H oxidation of saturated hydrocarbons with molecular oxygen (1 atm) using a combination of Cu(OAc)2 and acetonitrile at 70 °C. Related oxidation reactions such as epoxidation, Baeyer-Villiger reaction, acetoxylation of β-lactams with molecular oxygen and a suitable aldehyde at room temperature are described.
Collapse
|
15
|
Visible-Light-Driven Selective Air-Oxygenation of C-H Bond via CeCl 3 Catalysis in Water. CHEMSUSCHEM 2021; 14:2689-2693. [PMID: 33877736 DOI: 10.1002/cssc.202100682] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/01/2021] [Revised: 04/20/2021] [Indexed: 06/12/2023]
Abstract
Visible-light-induced C-H aerobic oxidation is an important chemical transformation that can be applied for the synthesis of aromatic ketones. High-cost catalysts and toxic solvents were generally needed in the present methodologies. Here, an efficient aqueous C-H aerobic oxidation protocol was reported. Through CeCl3 -mediated photocatalysis, a series of aromatic ketones were produced in moderate to excellent yields. With air as the oxidant, this reaction could be performed under mild conditions in water and demonstrated high activity and functional group tolerance. This method is economical, highly efficient, and environmentally friendly, and it will provide inspiration for the development of aqueous photochemical synthesis reactions.
Collapse
|
16
|
1,5,7-Triazabicyclo[4.4.0]dec-5-ene Enhances Activity of Peroxide Intermediates in Phosphine-Free α-Hydroxylation of Ketones. Angew Chem Int Ed Engl 2021; 60:6631-6638. [PMID: 33289252 DOI: 10.1002/anie.202014478] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 11/28/2020] [Indexed: 12/29/2022]
Abstract
The critical role of double hydrogen bonds was addressed for the aerobic α-hydroxylation of ketones catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), in the absence of either a metal catalyst or phosphine reductant. Experimental and theoretical investigations were performed to study the mechanism. In addition to initiating the reaction by proton abstraction, a more important role of TBD was revealed, that is, to enhance the oxidizing ability of peroxide intermediates, allowing DMSO to be used rather than commonly used phosphine reductants. Further characterizations with nuclear Overhauser effect spectroscopy (NOESY) confirmed the presence of double hydrogen bonds between TBD and the ketone, and kinetic studies suggested the attack of dioxygen on the TBD-enol adduct to be the rate-determining step. This work should encourage the application of TBD as a catalyst for oxidations.
Collapse
|
17
|
1,5,7‐Triazabicyclo[4.4.0]dec‐5‐ene Enhances Activity of Peroxide Intermediates in Phosphine‐Free α‐Hydroxylation of Ketones. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202014478] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
|
18
|
Efficient Palladium-Catalyzed Aerobic Oxidative Carbocyclization to Seven-Membered Heterocycles. Chemistry 2020; 26:15513-15518. [PMID: 32960479 PMCID: PMC7894550 DOI: 10.1002/chem.202004265] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2020] [Indexed: 11/09/2022]
Abstract
The use of molecular oxygen in palladium-catalyzed oxidation reactions is highly widespread in organic chemistry. However, the direct reoxidation of palladium by O2 is often kinetically unfavored, thus leading the deactivation of the palladium catalyst during the catalytic cycle. In the present work, we report a highly selective palladium-catalyzed carbocyclization of bisallenes to seven-membered heterocycles under atmospheric pressure of O2 . The use of a homogenous hybrid catalyst (Co(salophen)-HQ, HQ=hydroquinone) significantly promotes efficient electron transfer between the palladium catalyst and O2 through a low-energy pathway. This aerobic oxidative transformation shows broad substrate scope and functional group compatibility and allowed the preparation of O-containing seven-membered rings in good yields in most cases.
Collapse
|
19
|
Intramolecular C(sp 3 )-H Bond Oxygenation by Transition-Metal Acylnitrenoids. Angew Chem Int Ed Engl 2020; 59:21706-21710. [PMID: 32729945 PMCID: PMC7756817 DOI: 10.1002/anie.202009335] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2020] [Indexed: 02/01/2023]
Abstract
This study demonstrates for the first time that easily accessible transition‐metal acylnitrenoids can be used for controlled direct C(sp3)‐H oxygenations. Specifically, a ruthenium catalyst activates N‐benzoyloxycarbamates as nitrene precursors towards regioselective intramolecular C−H oxygenations to provide cyclic carbonates, hydroxylated carbamates, or 1,2‐diols. The method can be applied to the chemoselective C−H oxygenation of benzylic, allylic, and propargylic C(sp3)−H bonds. The reaction can be performed in an enantioselective fashion and switched in a catalyst‐controlled fashion between C−H oxygenation and C−H amination. This work provides a new reaction mode for the regiocontrolled and stereocontrolled conversion of C(sp3)‐H into C(sp3)−O bonds.
Collapse
|
20
|
Intramolecular C(sp
3
)–H Bond Oxygenation by Transition‐Metal Acylnitrenoids. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202009335] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
|
21
|
A Supported Bismuth Halide Perovskite Photocatalyst for Selective Aliphatic and Aromatic C-H Bond Activation. Angew Chem Int Ed Engl 2020; 59:5788-5796. [PMID: 31850662 PMCID: PMC7154683 DOI: 10.1002/anie.201915034] [Citation(s) in RCA: 75] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Indexed: 11/06/2022]
Abstract
Direct selective oxidation of hydrocarbons to oxygenates by O2 is challenging. Catalysts are limited by the low activity and narrow application scope, and the main focus is on active C-H bonds at benzylic positions. In this work, stable, lead-free, Cs3 Bi2 Br9 halide perovskites are integrated within the pore channels of mesoporous SBA-15 silica and demonstrate their photocatalytic potentials for C-H bond activation. The composite photocatalysts can effectively oxidize hydrocarbons (C5 to C16 including aromatic and aliphatic alkanes) with a conversion rate up to 32900 μmol gcat -1 h-1 and excellent selectivity (>99 %) towards aldehydes and ketones under visible-light irradiation. Isotopic labeling, in situ spectroscopic studies, and DFT calculations reveal that well-dispersed small perovskite nanoparticles (2-5 nm) possess enhanced electron-hole separation and a close contact with hydrocarbons that facilitates C(sp3 )-H bond activation by photoinduced charges.
Collapse
|
22
|
Copper‐Catalyzed Oxidative Benzylic C(sp
3
)−H Cyclization for the Synthesis of β‐Lactams. Chemistry 2020; 26:4496-4499. [DOI: 10.1002/chem.201905777] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2019] [Revised: 02/14/2020] [Indexed: 02/06/2023]
|
23
|
Non‐Heme‐Type Ruthenium Catalyzed Chemo‐ and Site‐Selective C−H Oxidation. Chem Asian J 2020; 15:762-765. [DOI: 10.1002/asia.202000134] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 02/17/2020] [Indexed: 01/17/2023]
|
24
|
A Supported Bismuth Halide Perovskite Photocatalyst for Selective Aliphatic and Aromatic C–H Bond Activation. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201915034] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
|
25
|
|
26
|
Carbon‐Nanotube‐Appended PAMAM Dendrimers Bearing Iron(II) α‐Keto Acid Complexes: Catalytic Non‐Heme Oxygenase Models. Chemistry 2019; 25:9191-9196. [DOI: 10.1002/chem.201901735] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 05/13/2019] [Indexed: 01/20/2023]
|
27
|
Iridium‐Catalyzed Direct C4‐ and C7‐Selective Alkynylation of Indoles Using Sulfur‐Directing Groups. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201904709] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
|
28
|
Iridium-Catalyzed Direct C4- and C7-Selective Alkynylation of Indoles Using Sulfur-Directing Groups. Angew Chem Int Ed Engl 2019; 58:9856-9860. [PMID: 31115135 DOI: 10.1002/anie.201904709] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2019] [Indexed: 12/12/2022]
Abstract
Indoles and their analogues have been one of the most ubiquitous heterocycles during the past century, and extensive studies have been conducted to establish practical synthetic methods for their derivatives. In particular, selective functionalization of the poorly reactive benzenoid core over the pyrrole ring has been a great challenge. Reported herein is an iridium-catalyzed direct alkynylation of the indole C4- and C7-positions with the assistance of sulfur directing groups. This transformation shows a wide range of functional-group tolerance with exceptional site selectivity. The directing group can be either easily removed or transformed after catalysis. The synthetic utility of the alkyne fragment is demonstrated by the derivatization into the core structure of natural indole alkaloids.
Collapse
|