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Alkyl Cyclopropyl Ketones in Catalytic Formal [3 + 2] Cycloadditions: The Role of SmI 2 Catalyst Stabilization. J Am Chem Soc 2024; 146:12799-12807. [PMID: 38662638 PMCID: PMC11082888 DOI: 10.1021/jacs.4c03073] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2024] [Revised: 04/10/2024] [Accepted: 04/12/2024] [Indexed: 05/09/2024]
Abstract
Alkyl cyclopropyl ketones are introduced as versatile substrates for catalytic formal [3 + 2] cycloadditions with alkenes and alkynes and previously unexplored enyne partners, efficiently delivering complex, sp3-rich products. The key to effectively engaging this relatively unreactive new substrate class is the use of SmI2 as a catalyst in combination with substoichiometric amounts of Sm0; the latter likely acting to prevent catalyst deactivation by returning SmIII to the catalytic cycle. In the absence of Sm0, background degradation of the SmI2 catalyst can outrun product formation. For the most recalcitrant alkyl cyclopropyl ketones, catalysis is "switched-on" using these new robust conditions, and otherwise unattainable products are delivered. Combined experimental and computational studies have been used to identify and probe reactivity trends among alkyl cyclopropyl ketones, including more complex bicyclic alkyl cyclopropyl ketones, which react quickly with various partners to give complex products. In addition to establishing alkyl cyclopropyl ketones as a new substrate class in a burgeoning field of catalysis, our study provides vital mechanistic insight and robust, practical approaches for the nascent field of catalysis with SmI2.
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2
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A blueprint for catalysis. Nat Chem 2024; 16:478. [PMID: 38448506 DOI: 10.1038/s41557-024-01438-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/08/2024]
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3
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Flavin-Mediated Photocatalysis Provides a General Platform for Sulfide C-H Functionalization. ACS Catal 2024; 14:2395-2401. [PMID: 38384945 PMCID: PMC10877610 DOI: 10.1021/acscatal.3c05785] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2023] [Revised: 01/16/2024] [Accepted: 01/17/2024] [Indexed: 02/23/2024]
Abstract
Functionalized sulfides are important in many areas of science, ranging from chemical biology through drug discovery to organic materials chemistry. Sulfides bearing pendant reactive groups in the α-position are particularly useful; however, methods for the selective valorization of simple sulfides or the late-stage functionalization of complex sulfides by the convenient addition of valuable functionality are underexplored. Here we exemplify a general reaction platform for sulfide functionalization by showcasing three modes of α-sulfur C-H functionalization; cyanation, alkenylation, and alkynylation. Using inexpensive and commercially available riboflavin tetraacetate and visible light, decoration of both feedstock and complex sulfides proceeds in a good yield and with high selectivity. Methionine-containing peptides can also be selectively functionalized and a tolerance screen using amino-acid dopants suggests that the platform is compatible with most amino-acid side chains and thus is a potential tool for bioconjugation.
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4
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Sulfonium Salts as Acceptors in Electron Donor-Acceptor Complexes. Angew Chem Int Ed Engl 2023; 62:e202303104. [PMID: 36959098 PMCID: PMC10952135 DOI: 10.1002/anie.202303104] [Citation(s) in RCA: 22] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2023] [Revised: 03/22/2023] [Accepted: 03/23/2023] [Indexed: 03/25/2023]
Abstract
The photoactivation of electron donor-acceptor complexes has emerged as a sustainable, selective and versatile strategy for the generation of radical species. Electron donor-acceptor (EDA) complexation, however, imposes electronic constraints on the donor and acceptor components and this can limit the range of radicals that can be generated using the approach. New EDA complexation strategies exploiting sulfonium salts allow radicals to be generated from native functionality. For example, aryl sulfonium salts, formed by the activation of arenes, can serve as the acceptor components in EDA complexes due to their electron-deficient nature. This "sulfonium tag" approach relaxes the electronic constraints on the parent substrate and dramatically expands the range of radicals that can be generated using EDA complexation. In this review, these new applications of sulfonium salts will be introduced and the areas of chemical space rendered accessible through this innovation will be highlighted.
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5
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Metal-Free Arylation of Benzothiophenes at C4 by Activation as their Benzothiophene S-Oxides. Angew Chem Int Ed Engl 2023; 62:e202302418. [PMID: 37000422 PMCID: PMC10953450 DOI: 10.1002/anie.202302418] [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: 02/16/2023] [Revised: 03/29/2023] [Accepted: 03/31/2023] [Indexed: 04/01/2023]
Abstract
Benzothiophenes, activated by oxidation to the corresponding S-oxides, undergo C-H/C-H-type coupling with phenols to give C4 arylation products. While an electron-withdrawing group at C3 of the benzothiophene is important, the process operates without a directing group and a metal catalyst, thus rendering it compatible with sensitive functionalities-e.g. halides and formyl groups. Quantum chemical calculations suggest a formal stepwise mechanism involving heterolytic cleavage of an aryloxysulfur species to give a π-complex of the corresponding benzothiophene and a phenoxonium cation. Subsequent addition of the phenoxonium cation to the C4 position of the benzothiophene is favored over the addition to C3; Fukui functions predict that the major regioisomer is formed at the more electron-rich position between C3 and C4. Varied selective manipulation of the benzothiophene products showcase the synthetic utility of the metal-free arylation process.
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6
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A catalytic alkene insertion approach to bicyclo[2.1.1]hexane bioisosteres. Nat Chem 2023; 15:535-541. [PMID: 36781910 DOI: 10.1038/s41557-023-01135-y] [Citation(s) in RCA: 37] [Impact Index Per Article: 37.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Accepted: 01/12/2023] [Indexed: 02/15/2023]
Abstract
C(sp3)-rich bicyclic hydrocarbon scaffolds, as exemplified by bicyclo[1.1.1]pentanes, play an increasingly high-profile role as saturated bioisosteres of benzenoids in medicinal chemistry and crop science. Substituted bicyclo[2.1.1]hexanes (BCHs) are emerging bicyclic hydrocarbon bioisosteres for ortho- and meta-substituted benzenes, but are difficult to access. Therefore, a general synthetic route to BCHs is needed if their potential as bioisosteres is to be realized. Here we describe a broadly applicable catalytic approach that delivers substituted BCHs by intermolecular coupling between olefins and bicyclo[1.1.0]butyl (BCB) ketones. The SmI2-catalysed process works for a wide range of electron-deficient alkenes and substituted BCB ketones, operates with SmI2 loadings as low as 5 mol% and is underpinned by a radical relay mechanism that is supported by density functional theory calculations. The product BCH ketones have been shown to be versatile synthetic intermediates through selective downstream manipulation and the expedient synthesis of a saturated hydrocarbon analogue of the broad-spectrum antimicrobial, phthalylsulfathiazole.
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A Vitamin B 2 -Photocatalysed Approach to Methionine Analogues. Angew Chem Int Ed Engl 2022; 61:e202212158. [PMID: 36250805 PMCID: PMC10100050 DOI: 10.1002/anie.202212158] [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: 08/17/2022] [Indexed: 11/05/2022]
Abstract
Access to new non-canonical amino acid residues is crucial for medicinal chemistry and chemical biology. Analogues of the amino acid methionine have been far less explored-despite their use in biochemistry, pharmacology and peptide bioconjugation. This is largely due to limited synthetic access. Herein, we exploit a new disconnection to access non-natural methionines through the development of a photochemical method for the radical α-C-H functionalization of sulfides with alkenes, in water, using inexpensive and commercially-available riboflavin (vitamin B2 ) as a photocatalyst. Our photochemical conditions allow the two-step synthesis of novel methionine analogues-by radical addition to unsaturated amino acid derivatives-and the chemoselective modification of peptide side-chains to yield non-natural methionine residues within small peptides. The mechanism of the bio-inspired flavin photocatalysis has been probed by experimental, DFT and TDDFT studies.
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A Vitamin B 2-Photocatalysed Approach to Methionine Analogues. ANGEWANDTE CHEMIE (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 134:e202212158. [PMID: 38505624 PMCID: PMC10946832 DOI: 10.1002/ange.202212158] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/17/2022] [Indexed: 11/11/2022]
Abstract
Access to new non-canonical amino acid residues is crucial for medicinal chemistry and chemical biology. Analogues of the amino acid methionine have been far less explored-despite their use in biochemistry, pharmacology and peptide bioconjugation. This is largely due to limited synthetic access. Herein, we exploit a new disconnection to access non-natural methionines through the development of a photochemical method for the radical α-C-H functionalization of sulfides with alkenes, in water, using inexpensive and commercially-available riboflavin (vitamin B2) as a photocatalyst. Our photochemical conditions allow the two-step synthesis of novel methionine analogues-by radical addition to unsaturated amino acid derivatives-and the chemoselective modification of peptide side-chains to yield non-natural methionine residues within small peptides. The mechanism of the bio-inspired flavin photocatalysis has been probed by experimental, DFT and TDDFT studies.
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9
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Diastereoselective Radical 1,4-Ester Migration: Radical Cyclizations of Acyclic Esters with SmI 2. J Am Chem Soc 2022; 144:13946-13952. [PMID: 35858251 PMCID: PMC9377304 DOI: 10.1021/jacs.2c05972] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
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Reductive cyclizations of carbonyl compounds, mediated
by samarium(II)
diiodide (SmI2, Kagan’s reagent), represent an invaluable
platform to generate molecular complexity in a stereocontrolled manner.
In addition to classical ketone and aldehyde substrates, recent advances
in radical chemistry allow the cyclization of lactone and lactam-type
substrates using SmI2. In contrast, acyclic esters are
considered to be unreactive to SmI2 and their participation
in reductive cyclizations is unprecedented. Here, we report a diastereoselective
radical 1,4-ester migration process, mediated by SmI2,
that delivers stereodefined alkene hydrocarboxylation products via
radical cyclization of acyclic ester groups in α-carbomethoxy
δ-lactones. Isotopic labeling experiments and computational
studies have been used to probe the mechanism of the migration. We
propose that a switch in conformation redirects single electron transfer
from SmI2 to the acyclic ester group, rather than the “more
reactive” lactone carbonyl. Our study paves the way for the
use of elusive ketyl radicals, derived from acyclic esters, in SmI2-mediated reductive cyclizations.
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Abstract
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The therapeutic properties of Curcuma (ginger
and turmeric’s family) have long been known in traditional
medicine. However, only recently have guaiane-type sesquiterpenes
extracted from Curcuma phaeocaulis been
submitted to biological testing, and their enhanced bioactivity was
highlighted. Among these compounds, phaeocaulisin A has shown remarkable
anti-inflammatory and anticancer activity, which appears to be tied
to the unique bridged acetal moiety embedded in its tetracyclic framework.
Prompted by the promising biological profile of phaeocaulisin A and
by the absence of a synthetic route for its provision, we have implemented
the first enantioselective total synthesis of phaeocaulisin A in 17
steps with 2% overall yield. Our route design builds on the identification
of an enantioenriched lactone intermediate, tailored with both a ketone
moiety and a conjugated alkene system. Taking advantage of the umpolung
carbonyl-olefin coupling reactivity enabled by the archetypal single-electron
transfer (SET) reductant samarium diiodide (SmI2), the
lactone intermediate was submitted to two sequential SmI2-mediated cyclizations to stereoselectively construct the polycyclic
core of the natural product. Crucially, by exploiting the innate inner-sphere
nature of carbonyl reduction using SmI2, we have used a
steric blocking strategy to render sites SET-unreceptive and thus
achieve chemoselective reduction in a complex substrate. Our asymmetric
route enabled elucidation of the naturally occurring isomer of phaeocaulisin
A and provides a synthetic platform to access other guaiane-type sesquiterpenes
from C. phaeocaulis—as well
as their synthetic derivatives—for medicinal chemistry and
drug design.
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Modular synthesis of unsymmetrical [1]benzothieno[3,2- b][1]benzothiophene molecular semiconductors for organic transistors. Chem Sci 2022; 13:421-429. [PMID: 35126974 PMCID: PMC8730195 DOI: 10.1039/d1sc05070b] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Accepted: 11/27/2021] [Indexed: 12/23/2022] Open
Abstract
A modular approach to underexplored, unsymmetrical [1]benzothieno[3,2-b][1]benzothiophene (BTBT) scaffolds delivers a library of BTBT materials from readily available coupling partners by combining a transition-metal free Pummerer CH-CH-type cross-coupling and a Newman-Kwart reaction. This effective approach to unsymmetrical BTBT materials has allowed their properties to be studied. In particular, tuning the functional groups on the BTBT scaffold allows the solid-state assembly and molecular orbital energy levels to be modulated. Investigation of the charge transport properties of BTBT-containing small-molecule:polymer blends revealed the importance of molecular ordering during phase segregation and matching the highest occupied molecular orbital energy level with that of the semiconducting polymer binder, polyindacenodithiophene-benzothiadiazole (PIDTBT). The hole mobilities extracted from transistors fabricated using blends of PIDTBT with phenyl or methoxy functionalized unsymmetrical BTBTs were double those measured for devices fabricated using pristine PIDTBT. This study underscores the value of the synthetic methodology in providing a platform from which to study structure-property relationships in an underrepresented family of unsymmetrical BTBT molecular semiconductors.
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Inhibitors of the Bub1 spindle assembly checkpoint kinase: synthesis of BAY-320 and comparison with 2OH-BNPP1. ROYAL SOCIETY OPEN SCIENCE 2021; 8:210854. [PMID: 34925867 PMCID: PMC8672067 DOI: 10.1098/rsos.210854] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/13/2021] [Accepted: 11/18/2021] [Indexed: 06/14/2023]
Abstract
Bub1 is a serine/threonine kinase proposed to function centrally in mitotic chromosome alignment and the spindle assembly checkpoint (SAC); however, its role remains controversial. Although it is well documented that Bub1 phosphorylation of Histone 2A at T120 (H2ApT120) recruits Sgo1/2 to kinetochores, the requirement of its kinase activity for chromosome alignment and the SAC is debated. As small-molecule inhibitors are invaluable tools for investigating kinase function, we evaluated two potential Bub1 inhibitors: 2OH-BNPPI and BAY-320. After confirming that both inhibit Bub1 in vitro, we developed a cell-based assay for Bub1 inhibition. We overexpressed a fusion of Histone 2B and Bub1 kinase region, tethering it in proximity to H2A to generate a strong ectopic H2ApT120 signal along chromosome arms. Ectopic signal was effectively inhibited by BAY-320, but not 2OH-BNPP1 at concentrations tested. In addition, only BAY-320 was able to inhibit endogenous Bub1-mediated Sgo1 localization. Preliminary experiments using BAY-320 suggest a minor role for Bub1 kinase activity in chromosome alignment and the SAC; however, BAY-320 may exhibit off-target effects at the concentration required. Thus, 2OH-BNPP1 may not be an effective Bub1 inhibitor in cellulo, and while BAY-320 can inhibit Bub1 in cells, off-target effects highlight the need for improved Bub1 inhibitors.
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13
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Modular Synthesis of Stereodefined Benzocyclobutene Derivatives via Sequential Cu- and Pd-Catalysis. ACS Catal 2021. [DOI: 10.1021/acscatal.1c04496] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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14
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Enantioselective Copper-Catalyzed Borylative Cyclization for the Synthesis of Quinazolinones. Angew Chem Int Ed Engl 2021; 60:14355-14359. [PMID: 33847459 PMCID: PMC8252434 DOI: 10.1002/anie.202103259] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2021] [Indexed: 12/15/2022]
Abstract
Quinazolinones are common substructures in molecules of medicinal importance. We report an enantioselective copper-catalyzed borylative cyclization for the assembly of privileged pyrroloquinazolinone motifs. The reaction proceeds with high enantio- and diastereocontrol, and can deliver products containing quaternary stereocenters. The utility of the products is demonstrated through further manipulations.
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15
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Enantioselective Copper‐Catalyzed Borylative Cyclization for the Synthesis of Quinazolinones. Angew Chem Int Ed Engl 2021. [DOI: 10.1002/ange.202103259] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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16
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Abstract
Ketyl radicals are valuable reactive intermediates for synthesis and are used extensively to construct complex, functionalized products from carbonyl substrates. Single electron transfer (SET) reduction of the C
Created by potrace 1.16, written by Peter Selinger 2001-2019
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O bond of aldehydes and ketones is the classical approach for the formation of ketyl radicals and metal reductants are the archetypal reagents employed. The past decade has, however, witnessed significant advances in the generation and harnessing of ketyl radicals. This tutorial review highlights recent, exciting developments in the chemistry of ketyl radicals by comparing the varied contemporary – for example, using photoredox catalysts – and more classical approaches for the generation and use of ketyl radicals. The review will focus on different strategies for ketyl radical generation, their creative use in new synthetic protocols, strategies for the control of enantioselectivity, and detailed mechanisms where appropriate. Ketyl radicals are valuable reactive intermediates for synthesis. This review highlights exciting recent developments in the chemistry of ketyl radicals by comparing contemporary and more classical approaches for their generation and use.![]()
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SmI 2-Catalyzed Intermolecular Coupling of Cyclopropyl Ketones and Alkynes: A Link between Ketone Conformation and Reactivity. J Am Chem Soc 2021; 143:3655-3661. [PMID: 33629852 PMCID: PMC8028054 DOI: 10.1021/jacs.1c01356] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The archetypal single electron transfer reductant, samarium(II) diiodide (SmI2, Kagan's reagent), remains one of the most important reducing agents and mediators of radical chemistry after four decades of widespread use in synthesis. While the chemistry of SmI2 is very often unique, and thus the reagent is indispensable, it is almost invariably used in superstoichiometric amounts, thus raising issues of cost and waste. Of the few reports of the use of catalytic SmI2, all require the use of superstoichiometric amounts of a metal coreductant to regenerate Sm(II). Here, we describe a SmI2-catalyzed intermolecular radical coupling of aryl cyclopropyl ketones and alkynes. The process shows broad substrate scope and delivers a library of decorated cyclopentenes with loadings of SmI2 as low as 15 mol %. The radical relay strategy negates the need for a superstoichiometric coreductant and additives to regenerate SmI2. Crucially, our study uncovers an intriguing link between ketone conformation and efficient cross-coupling and thus provides an insight into the mechanism of radical relays involving SmI2. The study lays further groundwork for the future use of the classical reagent SmI2 in contemporary radical catalysis.
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18
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Single-Scan Selective Excitation of Individual NMR Signals in Overlapping Multiplets. Angew Chem Int Ed Engl 2021; 60:666-669. [PMID: 32965750 PMCID: PMC7839668 DOI: 10.1002/anie.202011642] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2020] [Revised: 09/17/2020] [Indexed: 11/08/2022]
Abstract
2D NMR is an immensely powerful structural tool but it is time-consuming. Targeting individual chemical groups by selective excitation in a 1D experiment can give the information required far more quickly. A major problem, however, is that proton NMR spectra are often extensively overlapped, so that in practice only a minority of sites can be selectively excited. Here we overcome that problem using a fast, single-scan method that allows selective excitation of the signals of a single proton multiplet even where it is severely overlapped by other multiplets. The advantages of the method are illustrated in a selective 1D NOESY experiment, the most efficient way to determine relative configuration unambiguously by NMR. The new approach presented here has the potential to broaden significantly the applicability of selective excitation and unlock its real potential for many other experiments.
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20
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Single‐Scan Selective Excitation of Individual NMR Signals in Overlapping Multiplets. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202011642] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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21
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Abstract
Copper-catalyzed borylative multicomponent reactions (MCRs) involving olefins and C-N electrophiles are a powerful tool to rapidly build up molecular complexity. The products from these reactions contain multiple functionalities, such as amino, cyano and boronate groups, that are ubiquitous in medicinal and process chemistry programs. Copper-catalyzed MCRs are particularly attractive because they use a relatively abundant and non-toxic catalyst to selectively deliver high-value products from simple feedstocks such as olefins. In this Minireview, we explore this rapidly emerging field and survey the borylative union of allenes, dienes, styrenes and other olefins, with imines, nitriles and related C-N electrophiles.
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22
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Abstract
The copper-catalyzed functionalization of enyne derivatives has recently emerged as a powerful approach in contemporary synthesis. Enynes are versatile and readily accessible substrates that can undergo a variety of reactions to yield densely functionalized, enantioenriched products. In this perspective, we review copper-catalyzed transformations of enynes, such as boro- and hydrofunctionalizations, copper-mediated radical difunctionalizations, and cyclizations. Particular attention is given to the regiodivergent functionalization of 1,3-enynes, and the current mechanistic understanding of such processes.
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23
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Trifluoromethyl Sulfoxides: Reagents for Metal‐Free C−H Trifluoromethylthiolation. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202005531] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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24
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Trifluoromethyl Sulfoxides: Reagents for Metal-Free C-H Trifluoromethylthiolation. Angew Chem Int Ed Engl 2020; 59:15918-15922. [PMID: 32463942 PMCID: PMC7540508 DOI: 10.1002/anie.202005531] [Citation(s) in RCA: 35] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Revised: 05/21/2020] [Indexed: 12/22/2022]
Abstract
Trifluoromethyl sulfoxides are a new class of trifluoromethylthiolating reagent. The sulfoxides engage in metal-free C-H trifluoromethylthiolation with a range of (hetero)arenes. The method is also applicable to the functionalization of important compound classes, such as ligand derivatives and polyaromatics, and in the late-stage trifluoromethylthiolation of medicines and agrochemicals. The isolation and characterization of a sulfonium salt intermediate supports an interrupted Pummerer reaction mechanism.
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26
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27
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Enantio- and Diastereoselective Synthesis of Homopropargyl Amines by Copper-Catalyzed Coupling of Imines, 1,3-Enynes, and Diborons. Angew Chem Int Ed Engl 2020; 59:4879-4882. [PMID: 31917893 PMCID: PMC7383811 DOI: 10.1002/anie.201915191] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Indexed: 12/16/2022]
Abstract
An efficient, enantio- and diastereoselective, copper-catalyzed coupling of imines, 1,3-enynes, and diborons is reported. The process shows broad substrate scope and delivers complex, chiral homopropargyl amines; useful building blocks on the way to biologically-relevant compounds. In particular, functionalized homopropargyl amines bearing up to three contiguous stereocenters can be prepared in a single step.
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Cascades, Catalysis and Chiral Ligand Control with SmI₂; The Rebirth of a Reagent. Chimia (Aarau) 2020; 74:18-22. [PMID: 32200782 DOI: 10.2533/chimia.2020.18] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
This review focuses on recent developments from our laboratory in the field of radical reactions mediated by the archetypal reductive single electron transfer (SET) reagent, SmI₂. Namely, we have expanded the scope of reducible carbonyl moieties to esters and amides and have exploited the resultant ketyl radicals in radical cascade reactions that generate unprecedented scaffolds. Moreover, we have taken the first steps to address the long-standing challenges of catalysis and chiral ligand control associated with the reagent.
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Enantio‐ and Diastereoselective Synthesis of Homopropargyl Amines by Copper‐Catalyzed Coupling of Imines, 1,3‐Enynes, and Diborons. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.201915191] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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30
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Abstract
A metal-free, oxidative coupling of phenols with various nucleophiles, including arenes, 1,3-diketones and other phenols, is reported. Cross-coupling is mediated by a sulfoxide which inverts the reactivity of the phenol partner. Crucially, the process shows high selectivity for cross-versus homo-coupling and allows efficient access to a variety of aromatic scaffolds including biaryls, benzofurans and, through an iterative procedure, aromatic oligomers. A metal-free, oxidative coupling of phenols with various nucleophiles, including arenes, 1,3-diketones and other phenols, is reported.![]()
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Abstract
SmI2-catalyzed radical cascade cyclizations were used to generate complex carbocyclic products bearing quaternary stereocenters with high selectivity. Bicyclic scaffolds containing four contiguous stereocenters and one quaternary stereocenter were obtained in excellent yields (up to 99%) and with high diastereocontrol by using 5 mol% of SmI2 at ambient temperature in the absence of co-reductants or additives. Mechanistic studies support a radical relay mechanism.
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32
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Copper-Catalyzed Functionalization of 1,3-Dienes: Hydrofunctionalization, Borofunctionalization, and Difunctionalization. ACS Catal 2019. [DOI: 10.1021/acscatal.9b04767] [Citation(s) in RCA: 95] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Diastereoselective Hydroxyethylation of
β
‐Hydroxyketones: A
Reformatsky
Cyclization‐Lactone Reduction Cascade Mediated by SmI
2
−H
2
O. Helv Chim Acta 2019. [DOI: 10.1002/hlca.201900227] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
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Metal‐Free Synthesis of Benzothiophenes by Twofold C−H Functionalization: Direct Access to Materials‐Oriented Heteroaromatics. Angew Chem Int Ed Engl 2019; 58:15675-15679. [DOI: 10.1002/anie.201908319] [Citation(s) in RCA: 29] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2019] [Revised: 08/15/2019] [Indexed: 11/08/2022]
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Metal‐Free Synthesis of Benzothiophenes by Twofold C−H Functionalization: Direct Access to Materials‐Oriented Heteroaromatics. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201908319] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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Transition-Metal-Free Cross-Coupling of Benzothiophenes and Styrenes in a Stereoselective Synthesis of Substituted (E,Z)-1,3-Dienes. Angew Chem Int Ed Engl 2019; 58:8779-8783. [PMID: 30964596 DOI: 10.1002/anie.201902903] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2019] [Indexed: 01/14/2023]
Abstract
A transition metal-free one-pot stereoselective approach to substituted (E,Z)-1,3-dienes was developed by using an interrupted Pummerer reaction/ligand-coupling strategy. Readily available benzothiophene S-oxides, which can be conveniently prepared by oxidation of the parent benzothiophenes, undergo Pummerer coupling with styrenes. Reaction of the resultant sulfonium salts with alkyllithium/magnesium reagents generates underexploited hypervalent sulfurane intermediates that undergo selective ligand coupling, resulting in dismantling of the benzothiophene motif and the formation of decorated (E,Z)-1,3-dienes.
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Transition‐Metal‐Free Cross‐Coupling of Benzothiophenes and Styrenes in a Stereoselective Synthesis of Substituted (
E,Z
)‐1,3‐Dienes. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201902903] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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38
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The Interrupted Pummerer Reaction in a Sulfoxide‐Catalyzed Oxidative Coupling of 2‐Naphthols. Angew Chem Int Ed Engl 2019; 58:7813-7817. [DOI: 10.1002/anie.201903492] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2019] [Indexed: 12/20/2022]
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Pummerer chemistry of benzothiophene S-oxides: Metal-free alkylation and arylation of benzothiophenes. PHOSPHORUS SULFUR 2019. [DOI: 10.1080/10426507.2019.1602626] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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The Interrupted Pummerer Reaction in a Sulfoxide‐Catalyzed Oxidative Coupling of 2‐Naphthols. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201903492] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Abstract
Catalytic radical relays are an attractive tool for the rapid construction of complex molecular architectures.
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Transition-Metal-Free Synthesis of C3-Arylated Benzofurans from Benzothiophenes and Phenols. Org Lett 2018; 20:7498-7503. [DOI: 10.1021/acs.orglett.8b03267] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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45
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46
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Regiodivergent Copper Catalyzed Borocyanation of 1,3-Dienes. Angew Chem Int Ed Engl 2018; 57:11305-11309. [DOI: 10.1002/anie.201806169] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Indexed: 01/19/2023]
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47
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48
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An Interrupted Pummerer/Nickel-Catalysed Cross-Coupling Sequence. Angew Chem Int Ed Engl 2018; 57:9785-9789. [PMID: 29882623 DOI: 10.1002/anie.201805396] [Citation(s) in RCA: 74] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2018] [Indexed: 12/24/2022]
Abstract
An interrupted Pummerer/nickel-catalysed cross-coupling strategy has been developed and used in the elaboration of styrenes. The operationally simple method can be carried out as a one-pot process, involves the direct formation of stable alkenyl sulfonium salt intermediates, utilises a commercially available sulfoxide, catalyst, and ligand, operates at ambient temperature, accommodates sp-, sp2 -, and sp3 -hybridised organozinc coupling partners, and delivers functionalised styrene products in high yields over two steps. An interrupted Pummerer/cyclisation approach has also been used to access carbo- and heterocyclic alkenyl sulfonium salts for cross-coupling.
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Synthesis of C2 Substituted Benzothiophenes via an Interrupted Pummerer/[3,3]-Sigmatropic/1,2-Migration Cascade of Benzothiophene S
-Oxides. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201801982] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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