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1.
RSC Adv ; 14(18): 12528-12532, 2024 Apr 16.
Artigo em Inglês | MEDLINE | ID: mdl-38638815

RESUMO

Oxamic acids where shown to add to imines, providing a broad range of α-aminoacid amides in generally good yields. The process is efficient on pre-formed imines but may also be conducted using a 3-component strategy by simply mixing aldehydes, amines and oxamic acids in the presence of ferrocene, acting both as a photocatalyst under visible light and as a Lewis acid. The reaction proceeds through the addition onto the imine of a carbamoyl radical intermediate generated through a charge transfer from the carboxylate ligand to a Fe(iii) species (LMCT).

2.
Chem Commun (Camb) ; 59(76): 11369-11372, 2023 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-37665260

RESUMO

Dual Ni and Ir catalysis enables the preparation of arylsilanes having a (TMS)3Si substituent from the corresponding aryl bromides and (TMS)3SiH at 30 °C using visible-light irradiation. This protocol avoids strong bases, high temperature and air and moisture sensitive silyl reagents, providing the expected arylsilanes in moderate to good yields. The reaction was shown to proceed through a silyl radical, likely generated by hydrogen atom abstraction from (TMS)3SiH by a bromide radical.

3.
Org Lett ; 25(17): 3072-3077, 2023 May 05.
Artigo em Inglês | MEDLINE | ID: mdl-37092716

RESUMO

Visible-light-mediated intramolecular site-selective δ-C(sp3)-H bond arylation of aliphatic trifluoromethanesulfonamides was developed. The reaction proceeds through a radical cascade, including the generation of a sulfonamidyl radical, which triggers a 1,5-hydrogen atom transfer, affording a δ-C-centered radical, which finally cyclized onto a neighboring thiopolyfluoroaryl moiety to deliver a range of synthetically useful thiochromanes. The cyclization process occurs through two distinct pathways depending upon the nature of the substituent X ortho to the native C-S bond.

4.
Chemistry ; 29(15): e202202963, 2023 Mar 13.
Artigo em Inglês | MEDLINE | ID: mdl-36583591

RESUMO

The PIDA-mediated oxidative decarboxylation of oxamic acids in the presence of alcohols is shown to afford the corresponding urethanes under thermal conditions. Computational and experimental mechanistic exploration allows to rationalize the different reactivity of PIDA as compared to related cyclic BI-OAc and highlights the importance of the enhanced acidity of the proton in the carbamoyl radical intermediate.

5.
Chem Commun (Camb) ; 58(60): 8452, 2022 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-35838002

RESUMO

Correction for 'Oxamic acids: useful precursors of carbamoyl radicals' by Ikechukwu Martin Ogbu et al., Chem. Commun., 2022, 58, 7593-7607, https://doi.org/10.1039/D2CC01953A.

6.
Chem Commun (Camb) ; 58(63): 8802-8805, 2022 Aug 04.
Artigo em Inglês | MEDLINE | ID: mdl-35838178

RESUMO

Photocatalyzed oxidative decarboxylation of oxamic acids under near-infrared irradiation using Os(bptpy)2(PF6)2 as catalyst is reported. The reaction was applied to the synthesis of urethanes and heterocyclic amides. Mechanistic studies and comparative penetration depths between the NIR and the visible light mediated processes are discussed.

7.
Chem Commun (Camb) ; 58(55): 7593-7607, 2022 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-35735051

RESUMO

This review article describes the recent development in the chemistry of carbamoyl radicals generated from oxamic acids. This mild and efficient method compares well with previous methods of generation of these nucleophilic radicals. The oxidative decarboxylation of oxamic acids can be mediated through thermal, photochemical, electrochemical or photoelectrochemical means, generating carbamoyl radicals, which may further add to unsaturated systems to provide a broad range of important amides. Oxidative decarboxylation of oxamic acids also offers a straightforward entry for the preparation of urethanes, ureas, and thioureas.


Assuntos
Amidas , Ácido Oxâmico , Oxirredução , Ureia
8.
Chemistry ; 28(16): e202200088, 2022 Mar 16.
Artigo em Inglês | MEDLINE | ID: mdl-35084786

RESUMO

The total enantioselective synthesis of (+)-eucophylline 1 was achieved using as a key-structural motif a chiral piperidinone bearing the natural product all-carbon quaternary stereocenter. The elaboration of the latter is based on two strategies relying on the free-radical carbo-cyanation and sulfonyl-cyanation respectively of enantiopure substituted cyclopropenes and cyclobutenes. Co- or Ni-boride reduction of the nitrile functional group along with the cyclopropane and cyclobutane ring-opening then led to the formation of the chiral piperidinone ring. Further elaboration of the latter into the key 1-azabicyclo[3.3.1]nonane motif followed by its coupling with a 2-cyanoaniline allowed the formation of the tetrahydrobenzo[b][1,8]-naphthyridine skeleton of 1, which was finally accessible in 17 steps and 5.9 % overall yield from 1,1-dibromobutene.


Assuntos
Compostos Azabicíclicos , Ciclobutanos , Compostos Azabicíclicos/química , Ciclobutanos/química , Radicais Livres , Estereoisomerismo
9.
Chemistry ; 27(62): 15496-15500, 2021 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-34472137

RESUMO

The structure determination of a series of biphenylsilyloxonium cations through NMR and XRD studies, supported by DFT calculations was carried out, allowing to get insights into the origin of the oxygen pyramidalization in biphenyl and binaphthylsilyl oxoniums. Low barrier of inversion in the oxygenyl series points toward a key role of the biaryl axis in the inversion of configuration at the oxygen center.


Assuntos
Espectroscopia de Ressonância Magnética , Cátions
10.
ERJ Open Res ; 7(1)2021 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-33732743

RESUMO

In severe obstructive sleep apnoea, a soft cervical collar was well tolerated at night in 10 patients with no changes in polygraphy results. With the same design, a randomised controlled trial would need 246 inclusions for conclusive results. https://bit.ly/2KiU3j1.

11.
Chem Commun (Camb) ; 56(81): 12226-12229, 2020 Oct 13.
Artigo em Inglês | MEDLINE | ID: mdl-32926019

RESUMO

Urethane synthesis via oxidative decarboxylation of oxamic acids under mild electrochemical conditions is reported. This simple phosgene-free route to urethanes involves an in situ generation of isocyanates by anodic oxidation of oxamic acids in an alcoholic medium. The reaction is applicable to a wide range of oxamic acids, including chiral ones, and alcohols furnishing the desired urethanes in a one-pot process without the use of a chemical oxidant.

12.
Chem Commun (Camb) ; 56(85): 13013-13016, 2020 Oct 27.
Artigo em Inglês | MEDLINE | ID: mdl-32996936

RESUMO

A new efficient strategy to access benzylic carbamates through C-H activation is reported. The use of a catalytic amount of a Cu(i)/diimine ligand in combination with NFSI ((PhSO2)2NF) or F-TEDA-PF6 as oxidants and H2NCO2R as an amine source directly leads to the C-N bond formation at the benzylic position. The mild reaction conditions and the broad substrate scope make this transformation a useful method for the late-stage incorporation of a ubiquitous carbamate fragment onto hydrocarbons.

13.
Org Biomol Chem ; 18(16): 3007-3011, 2020 04 29.
Artigo em Inglês | MEDLINE | ID: mdl-32255144

RESUMO

Sterically hindered aminoarylboranes featuring atropisomerism about the C-B bond were prepared by addition of organomagnesium species onto readily accessible dialkylamine-borane complexes. Some of these aminoarylboranes, isosteres of vinyl styrene derivatives, were resolved by HPLC on the chiral stationary phase. They are the first examples of a non-biaryl type system which display slow rotation about a C-B bond.

14.
J Am Chem Soc ; 142(1): 564-572, 2020 01 08.
Artigo em Inglês | MEDLINE | ID: mdl-31814388

RESUMO

Pyridine- and quinoline-stabilized silyl cations have been prepared, and their structure in condensed phases unambiguously assigned using 1H, 13C, 15N, 29Si, and 1H DOSY NMR as well as X-ray diffraction studies. Solid state structures thus show in both cases a stabilization of the cationic silicon center through an N-Si interaction and formation of a highly strained four-membered ring system. Chiral memory at the silicon atom in these heterocycle-stabilized silyl cations was also established, leading to various levels of selectivity depending on the nature of the heterocycle. Lowest energy conformations of the starting silanes obtained through DFT calculations, along with the isolation and characterization of the Si-centered chiral silyl cation intermediates, finally allowed to propose a plausible hypothesis as to the configurational stability of these silyl cations.

15.
Org Lett ; 22(2): 575-579, 2020 Jan 17.
Artigo em Inglês | MEDLINE | ID: mdl-31874040

RESUMO

The photosensitized p-anisaldehyde-mediated addition of sulfonylcyanides onto the π-system of cyclobutenes is shown to afford highly functionalized cyclobutanes in high yields and diastereocontrol. The homochiral cyclobutene precursors are accessible on multigram scale in two steps through an asymmetric [2 + 2] cycloaddition/vinyl thioether reduction sequence. The enantiopure cyclobutylnitriles can be elaborated further through SmI2-mediated ring opening or converted into new enantiopure cyclobutenes through base-mediated sulfone elimination.

16.
Beilstein J Org Chem ; 15: 1822-1828, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31467602

RESUMO

Four-component coupling reactions between xanthogenates, alkenes, CO, and sulfonyl oxime ethers were studied. In the presence of hexabutylditin, working as a propagating radical reagent, the chain reaction proceeds, as expected, taking into account reagents polarities, affording the corresponding functionalized α-keto oximes. Although yields are modest, this rare one-pot four-component process is easy to carry out and the resulting compounds, bearing multiple functionalities, have the potential for further elaboration.

17.
Chemistry ; 25(3): 728-732, 2019 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-30351531

RESUMO

Pd-nanoparticle-catalyzed dehydrogenative coupling between various hydrosilanes and alcohols was shown to provide silyl ethers in good and reproducible yields. The synthetic methodology is effective for a wide range of simple and bulky silanes and secondary alcohols, while keeping various other functional groups intact. The procedure also exhibits high selectivity for the silylation of primary versus secondary alcohols in 1,2-diols, and allows the successive silylation of alkynols and hydrogenation of the triple bond to afford Z-alkenols in good yields.

18.
Chem Commun (Camb) ; 55(4): 466-469, 2019 Jan 03.
Artigo em Inglês | MEDLINE | ID: mdl-30547162

RESUMO

The generation of carbamoyl radicals, followed by their addition to heteroarenes, was performed under mild conditions through a metal-free photocatalyzed decarboxylation of oxamic acids. The process has been applied to the carbamoylation of heteroaromatic bases using α-aminoacid-derived oxamic acids, leading to the corresponding amides without racemization.

19.
Eur J Med Chem ; 161: 354-363, 2019 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-30384041

RESUMO

Pure diastereomeric spirocyclic analogs of fluorocortivazol were conveniently prepared by a short and efficient synthetic sequence recently developed in our laboratory. The structures and conformations of several key products were confirmed by single crystal X-ray diffraction analysis. Conformational assignments were also supported by DFT calculations. Biological evaluation led to the identification of a highly potent hGR agonist with excellent anti-inflammatory effects in the subnanomolar range. All tested compounds from this series were also selective versus the progesterone receptor.


Assuntos
Anti-Inflamatórios não Esteroides/farmacologia , Descoberta de Drogas , Receptores de Glucocorticoides/agonistas , Compostos de Espiro/farmacologia , Anti-Inflamatórios não Esteroides/síntese química , Anti-Inflamatórios não Esteroides/química , Relação Dose-Resposta a Droga , Humanos , Modelos Moleculares , Estrutura Molecular , Teoria Quântica , Compostos de Espiro/síntese química , Compostos de Espiro/química , Relação Estrutura-Atividade
20.
Chem Commun (Camb) ; 54(67): 9337-9340, 2018 Aug 16.
Artigo em Inglês | MEDLINE | ID: mdl-30073222

RESUMO

A sustainable metal-free route to urethanes and ureas based on a photocatalyzed oxidative decarboxylation of oxamic acids is described. The reaction includes in situ generation of an isocyanate from the oxamic acid, using an organic dye as a photocatalyst, a hypervalent iodine reagent as an oxidant and a light source, which trigger the free-radical decarboxylation. This protocol successfully avoids the isolation, purification and storage of carcinogenic isocyanates and allows elaboration of urethanes and ureas in a one-pot process from commercially available sources.

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