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A Pd-H/Isothiourea Cooperative Catalysis Approach to anti-Aldol Motifs: Enantioselective α-Alkylation of Esters with Oxyallenes. Angew Chem Int Ed Engl 2022; 61:e202201753. [PMID: 35307949 DOI: 10.1002/anie.202201753] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2022] [Indexed: 12/11/2022]
Abstract
The biological and therapeutic significance of natural products is a powerful impetus for the development of efficient methods to facilitate their construction. Accordingly, and reflecting the prevalence of β-oxy-carbonyl motifs, a sophisticated arsenal of aldol-based strategies has evolved that is contingent on the generation of single enolate isomers. Since this has the potential to compromise efficiency in reagent-based paradigms, direct catalysis-based solutions would be enabling. To complement the array of substrate-based strategies, and regulate enolate geometry at the catalyst level, a direct catalytic alkylation of esters with oxyallenes has been developed. Synergizing metal hydride reactivity with Lewis base catalysis has resulted in a broad reaction scope with useful levels of stereocontrol (up to >99 % ee). Facile derivatization of these ambiphilic linchpins is demonstrated, providing access to high-value vicinal stereocenter-containing motifs, including 1,2-amino alcohols.
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2
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A Pd−H/Isothiourea Cooperative Catalysis Approach to
anti
‐Aldol Motifs: Enantioselective α‐Alkylation of Esters with Oxyallenes**. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202201753] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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3
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A Comparative Study of High-Contrast Fluorescence Lifetime Probes for Imaging Amyloid in Tissue. J Phys Chem B 2021; 125:13710-13717. [PMID: 34883017 PMCID: PMC7615715 DOI: 10.1021/acs.jpcb.1c07762] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Optical imaging of protein aggregates in living and post-mortem tissue can often be impeded by unwanted fluorescence, prompting the need for novel methods to extract meaningful signal in complex biological environments. Historically, benzothiazolium derivatives, prominently Thioflavin T, have been the state-of-the-art fluorescent probes for amyloid aggregates, but their optical, structural, and binding properties typically limit them to in vitro applications. This study compares the use of novel uncharged derivative, PAP_1, with parent Thioflavin T as a fluorescence lifetime imaging probe. This is applied specifically to imaging recombinant α-synuclein aggregates doped into brain tissue. Despite the 100-fold lower brightness of PAP_1 compared to that of Thioflavin T, PAP_1 binds to α-synuclein aggregates with an affinity several orders of magnitude greater than Thioflavin T; thus, we observe a specific decrease in the fluorescence lifetime of PAP_1 bound to α-synuclein aggregates, resulting in a separation of >1.4 standard deviations between PAP_1-stained brain tissue background and α-synuclein aggregates that is not observed with Thioflavin T. This enables contrast between highly fluorescent background tissue and amyloid fibrils that is attributed to the greater affinity of PAP_1 for α-synuclein aggregates, avoiding the substantial off-target staining observed with Thioflavin T.
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A Comparative Photophysical Study of Structural Modifications of Thioflavin T-Inspired Fluorophores. J Phys Chem Lett 2020; 11:8406-8416. [PMID: 32924494 PMCID: PMC8741274 DOI: 10.1021/acs.jpclett.0c01549] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
Abstract
The benzothiazolium salt, Thioflavin T (ThT), has been widely adopted as the "gold-standard" fluorescent reporter of amyloid in vitro. Its properties as a molecular rotor result in a large-scale (∼1000-fold) fluorescence turn-on upon binding to β-sheets in amyloidogenic proteins. However, the complex photophysics of ThT combined with the intricate and varied nature of the amyloid binding motif means these interactions are poorly understood. To study this important class of fluorophores, we present a detailed photophysical characterization and comparison of a novel library of 12 ThT-inspired fluorescent probes for amyloid protein (PAPs), where both the charge and donor capacity of the heterocyclic and aminobenzene components have been interrogated, respectively. This enables direct photophysical juxtaposition of two structural groups: the neutral "PAP" (class 1) and the charged "mPAP" fluorophores (class 2). We quantify binding and optical properties at both the bulk and single-aggregate levels with some derivatives showing higher aggregate affinity and brightness than ThT. Finally, we demonstrate their abilities to perform super-resolution imaging of α-synuclein fibrils with localization precisions of ∼16 nm. The properties of the derivatives provide new insights into the relationship between chemical structure and function of benzothiazole probes.
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5
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Enantioselective Syntheses of
Strychnos
and
Chelidonium
Alkaloids through Regio‐ and Stereocontrolled Cooperative Catalysis. Angew Chem Int Ed Engl 2020. [DOI: 10.1002/ange.202005151] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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6
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Enantioselective Syntheses of
Strychnos
and
Chelidonium
Alkaloids through Regio‐ and Stereocontrolled Cooperative Catalysis. Angew Chem Int Ed Engl 2020; 59:17556-17564. [DOI: 10.1002/anie.202005151] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Indexed: 02/06/2023]
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7
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Abstract
Neurodegenerative diseases such as Alzheimer's and Parkinson's are associated with protein misfolding and aggregation. Recent studies suggest that the small, rare and heterogeneous oligomeric species, formed early on in the aggregation process, may be a source of cytotoxicity. Thioflavin T (ThT) is currently the gold-standard fluorescent probe for the study of amyloid proteins and aggregation processes. However, the poor photophysical and binding properties of ThT impairs the study of oligomers. To overcome this challenge, we have designed Thioflavin X, (ThX), a next-generation fluorescent probe which displays superior properties; including a 5-fold increase in brightness and 7-fold increase in binding affinity to amyloidogenic proteins. As an extrinsic dye, this can be used to study unique structural amyloid features both in bulk and on a single-aggregate level. Furthermore, ThX can be used as a super-resolution imaging probe in single-molecule localisation microscopy. Finally, the improved optical properties (extinction coefficient, quantum yield and brightness) of ThX can be used to monitor structural differences in oligomeric species, not observed via traditional ThT imaging.
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8
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Tertiary Amine Lewis Base Catalysis in Combination with Transition Metal Catalysis. Top Curr Chem (Cham) 2020; 378:16. [PMID: 31942682 DOI: 10.1007/s41061-020-0279-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2019] [Accepted: 01/02/2020] [Indexed: 01/03/2023]
Abstract
The cooperation between two orthogonal catalytic events during the formation of carbon-carbon and carbon-heteroatom bonds has emerged as an effective strategy for enantioselective chemical synthesis. In recent years, a number of pioneering investigations have described useful chemical synthesis methods whereby the reactivity or nucleophile-electrophile combinations can be fine-tuned or extended far beyond the effect and influence of a single catalyst. The recognition of this has had profound implications for the development cooperative catalysis as a field and has provided a foundation for the development of broadly useful chemical synthesis methods. This chapter focuses on the combination of tertiary amine Lewis base and transition metal catalysts, which the authors hope will simulate further developments and advances.
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9
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Hydrogen bonding in high-Z′ molecular structures. Acta Crystallogr A Found Adv 2019. [DOI: 10.1107/s0108767319098842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
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10
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A Regio‐ and Stereodivergent Synthesis of Homoallylic Amines by a One‐Pot Cooperative‐Catalysis‐Based Allylic Alkylation/Hofmann Rearrangement Strategy. Angew Chem Int Ed Engl 2019. [DOI: 10.1002/ange.201905426] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
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11
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A Regio- and Stereodivergent Synthesis of Homoallylic Amines by a One-Pot Cooperative-Catalysis-Based Allylic Alkylation/Hofmann Rearrangement Strategy. Angew Chem Int Ed Engl 2019; 58:10521-10527. [PMID: 31132203 DOI: 10.1002/anie.201905426] [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: 05/01/2019] [Indexed: 01/19/2023]
Abstract
Herein, we report a modular synthetic route to linear and branched homoallylic amines that operates through a sequential one-pot Lewis base/transition-metal catalyzed allylic alkylation/Hofmann rearrangement strategy. This protocol is operationally trivial, proceeds from simple and easily prepared substrates and catalysts, and enables all aspects of regio- and stereoselectivity to be controlled through a conserved experimental protocol. Overall, the high levels of enantio-, regio-, and diastereoselectivity obtained, in concert with the ability to access orthogonally protected or free amines, render this a straightforward and effective approach for the preparation of useful enantioenriched homoallylic amines. We have also demonstrated the utility of the products in the context of pharmaceutical synthesis.
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Abstract
Epidithiodiketopiperazines (ETPs) possess remarkably diverse biological activities and have attracted significant synthetic attention. The preparation of analogues is actively pursued; however, they are structurally challenging, and more direct and modular methods for their synthesis are desirable. To this end, the utility of a bifunctional triketopiperazine building block for the straightforward synthesis of ETPs is reported. A modular strategy consisting of enolate alkylation followed by site-selective nucleophile addition enables the concise synthesis of (±)-hyalodendrin and a range of analogues.
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13
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An enantioselective synthesis of α-alkylated pyrroles via cooperative isothiourea/palladium catalysis. Org Biomol Chem 2019; 17:1787-1790. [PMID: 30483696 PMCID: PMC6499370 DOI: 10.1039/c8ob02600a] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Herein we describe the direct enantioselective Lewis base/Pd catalysed α-allylation of pyrrole acetic acid esters. This provides high isolated yields of highly enantioenriched products and exhibits broad reaction scope with respect to both reaction partners. The products can be readily elaborated in a manner which points towards potential applications in target directed synthesis.
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Enantioselective α-Allylation of Acyclic Esters Using B(pin)-Substituted Electrophiles: Independent Regulation of Stereocontrol Elements through Cooperative Pd/Lewis Base Catalysis. Chemistry 2018; 24:14378-14381. [PMID: 30011357 DOI: 10.1002/chem.201803543] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2018] [Indexed: 02/05/2023]
Abstract
Cooperation between a Lewis base and Pd catalyst enables the direct enantioselective α-functionalization of aryl and vinyl acetic acid esters using a bifunctional B(pin)-substituted electrophile. Critical to the success of this method was the recognition that both catalysts could control the necessary stereochemical aspects; the Lewis base catalyst controls the enantioselectivity of the reaction, whereas the Pd catalyst regulates alkenyl-B(pin) configuration. This is the first example of using cooperative catalysis to control both stereochemical features during Pd-catalyzed allylic alkylation.
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15
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Enantioselective α-Benzylation of Acyclic Esters Using π-Extended Electrophiles. Angew Chem Int Ed Engl 2018; 57:12102-12105. [PMID: 30011353 DOI: 10.1002/anie.201806742] [Citation(s) in RCA: 57] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2018] [Indexed: 11/06/2022]
Abstract
The first asymmetric cooperative Lewis base/palladium catalyzed benzylic alkylation of acyclic esters is reported. This reaction proceeds via stereodefined C1-ammonium enolate nucleophiles. Critical to its success was the identification of benzylic phosphate electrophiles, which were uniquely reactive. Alkylated products were obtained with very high levels of enantioselectivity, and this method has been applied toward the synthesis of the thrombin inhibitor DX-9065a.
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Traversing Steric Limitations by Cooperative Lewis Base/Palladium Catalysis: An Enantioselective Synthesis of α-Branched Esters Using 2-Substituted Allyl Electrophiles. Angew Chem Int Ed Engl 2018; 57:7800-7803. [PMID: 29701289 DOI: 10.1002/anie.201803277] [Citation(s) in RCA: 47] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2018] [Indexed: 11/10/2022]
Abstract
Cooperative catalysis enables the direct enantioselective α-allylation of linear prochiral esters with 2-substituted allyl electrophiles. Critical to the successful development of the method was the recognition that metal-centered reactivity and the source of enantiocontrol are independent. This feature is unique to simultaneous catalysis events and permits logical tuning of the supporting ligands without compromising enantioselectivity.
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17
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Traversing Steric Limitations by Cooperative Lewis Base/Palladium Catalysis: An Enantioselective Synthesis of α‐Branched Esters Using 2‐Substituted Allyl Electrophiles. Angew Chem Int Ed Engl 2018. [DOI: 10.1002/ange.201803277] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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18
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Si-Directed regiocontrol in asymmetric Pd-catalyzed allylic alkylations using C1-ammonium enolate nucleophiles. Tetrahedron 2018; 74:5383-5391. [PMID: 30559533 DOI: 10.1016/j.tet.2018.04.021] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Cooperative catalysis enables the direct enantioselective α-allylation of linear prochiral esters using Si-substituted allyl electrophiles. The Si-substituent directs the regioselectivity of enantioselective bond formation and provides products containing synthetically versatile pentafluorophenyl ester and vinylsilane moieties. Critical to the efficacy of this process was the recognition that the ancillary ligand on palladium could be altered to prevent formation of a deleterious ether by-product, whilst retaining enantioselectivity through the Lewis base catalyst. Flexibility such as this is unique to cooperative catalysis events and provides efficient access to an array of enantioenriched products that are orthogonally functionalized and easily modified.
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19
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Correction to 'Bifunctional fluorescent probes for detection of amyloid aggregates and reactive oxygen species'. ROYAL SOCIETY OPEN SCIENCE 2018; 5:180308. [PMID: 29658954 PMCID: PMC5882756 DOI: 10.1098/rsos.180308] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
[This corrects the article DOI: 10.1098/rsos.171399.].
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20
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Bifunctional fluorescent probes for detection of amyloid aggregates and reactive oxygen species. ROYAL SOCIETY OPEN SCIENCE 2018; 5:171399. [PMID: 29515860 PMCID: PMC5830749 DOI: 10.1098/rsos.171399] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2017] [Accepted: 01/08/2018] [Indexed: 05/30/2023]
Abstract
Protein aggregation into amyloid deposits and oxidative stress are key features of many neurodegenerative disorders including Parkinson's and Alzheimer's disease. We report here the creation of four highly sensitive bifunctional fluorescent probes, capable of H2O2 and/or amyloid aggregate detection. These bifunctional sensors use a benzothiazole core for amyloid localization and boronic ester oxidation to specifically detect H2O2. We characterized the optical properties of these probes using both bulk fluorescence measurements and single-aggregate fluorescence imaging, and quantify changes in their fluorescence properties upon addition of amyloid aggregates of α-synuclein and pathophysiological H2O2 concentrations. Our results indicate these new probes will be useful to detect and monitor neurodegenerative disease.
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22
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Uniting C1-Ammonium Enolates and Transition Metal Electrophiles via Cooperative Catalysis: The Direct Asymmetric α-Allylation of Aryl Acetic Acid Esters. J Am Chem Soc 2016; 138:5214-7. [DOI: 10.1021/jacs.6b01694] [Citation(s) in RCA: 106] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
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23
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Back Cover: Callipeltosides A, B and C: Total Syntheses and Structural Confirmation (Chem. Eur. J. 38/2015). Chemistry 2015. [DOI: 10.1002/chem.201583804] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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24
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Abstract
Since their isolation almost 20 years ago, the callipeltosides have been of long standing interest to the synthetic community owing to their unique structural features and inherent biological activity. Herein we present our full research effort that has led to the synthesis of these molecules. Key aspects of our final strategy include 1) synthesis of the C1-C9 pyran core (5) using an AuCl3 -catalysed cyclisation; 2) formation of C10-C22 vinyl iodide (55) by sequential bidirectional Stille reactions and 3) diastereoselective union of these advanced fragments by means of an alkenylzinc addition (d.r.=91:9 at C9). The common callipeltoside aglycon (4) was completed in a further five steps. Following this, all three sugar fragments were appended to provide the entire callipeltoside family. In addition to this, D-configured callipeltose B was synthesised and appended to the callipeltoside aglycon. The (1) H NMR spectrum of this molecule was found to be significantly different to the natural isolate, further supporting our assignment of callipeltoside B (2).
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25
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Convergent Total Syntheses of Callipeltosides A, B, and C. Angew Chem Int Ed Engl 2012; 51:9366-71. [DOI: 10.1002/anie.201204868] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2012] [Indexed: 11/11/2022]
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26
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27
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Highlights from the 47th EUCHEM conference on stereochemistry, Bürgenstock, Switzerland, May 2012. Chem Commun (Camb) 2012. [DOI: 10.1039/c2cc90366k] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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28
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29
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Abstract
Key steps in the synthesis of the C1-C16 polyketide fragment of ionomycin were the nucleophilic addition of an organocuprate to a neutral (eta3-allyl)iron complex and the construction of a beta-diketone moiety by the Rh-catalysed rearrangement of an alpha-diazo-beta-hydroxyketone.
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Direct Conversion of N-Methoxy-N-methylamides (Weinreb Amides) to Ketones via a Nonclassical Wittig Reaction. Org Lett 2005; 7:1427-9. [PMID: 15787523 DOI: 10.1021/ol050337b] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
[reaction: see text] N-Methoxy-N-methylamides (Weinreb amides) are converted efficiently into ketones by reaction with alkylidenetriphenylphosphoranes and in situ hydrolysis of the product.
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