Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 36
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Org Chem ; 89(13): 9695-9699, 2024 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-38965935

RESUMO

UV light-promoted synthesis of α-sulfonyl amides from N-sulfonyl ynamides without any additives is reported. The reaction proceeds through a radical chain mechanism involving the photoinduced cleavage of the nitrogen-sulfur bond and addition of an electrophilic sulfonyl radical to the triple bond of the ynamide followed by ß-fragmentation of the sulfonyl group leading to a ketenimine hydrated upon workup. This highly efficient rearrangement leads, after acidic treatment, to a wide range of α-sulfonyl amides in high yields.

2.
J Org Chem ; 88(4): 2464-2473, 2023 Feb 17.
Artigo em Inglês | MEDLINE | ID: mdl-36715251

RESUMO

Mn(OAc)3/Cu(OAc)2-mediated reaction between ynamides, derived from oxazolidone or 3-methylindole carboxylate, and cyclic α-dicarbonyl radicals led to the one-pot synthesis of 2-aminofurans. The transformation involves addition of the α-dicarbonyl radical to ynamide, oxidation to ketene-iminium, and polar cyclization steps to provide original persubstituted 2-aminofurans in good to excellent yields. This work represents the first radical route for the synthesis of furans from ynamides.

3.
Chem Rev ; 122(6): 5842-5976, 2022 03 23.
Artigo em Inglês | MEDLINE | ID: mdl-35073048

RESUMO

Benefiting from the impressive increase in fundamental knowledge, the last 20 years have shown a continuous burst of new ideas and consequently a plethora of new catalytic methods for enantioselective radical reactions. This review aims to provide a complete survey of progress achieved over this latter period. The first part of this review focuses on the use of chiral organocatalysts, and these include catalysts covalently linked to the substrate and those that interact with the substrate by weaker interactions like hydrogen bonds. The second part of the review is devoted to transition-metal redox catalysis which is organized according to increasing atomic number for the first-row transition metals (Ti, Cr, Fe, Mn, Co, Ni, Cu). Bioinspired manganese- and iron-mediated hydroxylations and oxidations are also discussed. A specific section is dedicated to the reactivity of Ru, Rh, and Ir complexes as Lewis acids with a special focus on complexes chiral at metal. Absorption of photons result in different events such as energy transfer, single-electron transfer, and hydrogen-atom transfer facilitating the formation of radicals. Organocatalysis has been successfully combined with photocatalysts, a reactivity which has opened new pathways enlarging the number of radical precursors available. The merger of photocatalysis with organo- or metalla-photocatalysis has brought novelty and allowed for the discovery of a large number of original transformations. The use of enzyme-catalyzed reactions involving radical intermediates which also largely benefit from visible-light irradiation are included in the review. This review provides a comprehensive inventory of progress in enantioselective radical reactions with a goal of detailing the reaction mechanisms involved in these transformations such that any nonspecialist could find their own creativity to invent yet unknown applications.


Assuntos
Hidrogênio , Ácidos de Lewis , Catálise , Hidrogênio/química , Oxirredução , Estereoisomerismo
4.
J Org Chem ; 85(6): 4114-4121, 2020 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-32069414

RESUMO

Rather surprisingly, C-C bond formation through "intermolecular" radical addition to internal ynamides has never been reported. Actually, ynamides are excellent acceptors for "electrophilic" carbon-centered radicals. These processes enable the introduction of functionalized alkyl chains at Cß, groups that have not yet been introduced via the addition of organometallics. Radical carboiodination affords persubstituted α-iodo-enamides in moderate to high yield. The addition is totally stereoselective. Theoretical support to the mechanism and the scope and limitation of the reaction are discussed.

5.
Chemistry ; 23(35): 8375-8379, 2017 Jun 22.
Artigo em Inglês | MEDLINE | ID: mdl-28436112

RESUMO

Enantioenriched indenes were reached through a chirality conversion strategy using original axially chiral benzylidene cyclanes. Good to high remote diastereocontrol and excellent enantiocontrol were observed in this cascade involving copper-catalyzed homologation of terminal alkynes, in situ allenoate formation and Alder-ene cyclization.

6.
ACS Macro Lett ; 6(2): 117-120, 2017 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-35632879

RESUMO

New polysilsesquioxane-based lamellar materials, functionalized with radical precursors, were synthesized. They play a double role in the preparation of composite materials: first, as filler homogeneously dispersed in the monomer after delamination, second as radical initiator in photopolymerization. These polysilsesquioxanes enable fast and efficient photopolymerization upon UV light for thick samples. High conversions in monomers as well as the formation of hybrid polymers covalently linked to the filler are observed. This strategy, based on a double bottom-up approach, avoids the solubility/dispersion problem encountered in the classical preparation of composite polymers from preformed organic polymers.

7.
Chemistry ; 20(49): 16034-59, 2014 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-25345694

RESUMO

Hydrogen-atom transfer (HAT) counts amongst the most widely investigated routes to carbon-centered radicals. Intramolecular processes involving 1,5-HAT are widespread to promote regioselective radical "CH activation". The aim of this review is to draw up a comprehensive inventory of the less commonly encountered 1,n-radical translocations (n≠5) with the aim to update this topic with the most recent relevant data.

8.
J Org Chem ; 79(19): 9086-93, 2014 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-25198708

RESUMO

This article reports a theoretical study to explain how the intrinsic property of chirality is retained throughout the radical cascade rearrangement of an enantiopure chiral enyne-allene (bearing one stereogenic center) selected as a model for this family of reactions. Calculations at the MRPT2/6-31G(d)//CASSCF(10,10)/6-31G(d) level of theory were used to determine the entire reaction pathway which includes singlet state diradicals and closed-shell species. The cascade process involves three elementary steps, i.e., by chronological order: Myers-Saito cycloaromatization (M-S), intramolecular hydrogen atom transfer (HAT), and recombination of the resulting biradical. The enantiospecificity of the reaction results from a double transmission of the stereochemical information, from the original center to an axis and eventually from this axis to the final center. The first two steps lead to a transient diradical intermediate which retains the chirality via the conversion of the original static chirogenic element into a dynamic one, i.e., a center into an axis. The only available routes to the final closed-shell tetracyclic product imply rotations around two σ bonds (σ(C-C) and σ(C-N), bonds ß and α respectively). The theoretical calculations confirmed that the formation of the enantiomerically pure product proceeds via the nonracemizing rotation around the σ(C-C) pivot. They ruled out any rotation around the second σ(C-N) pivot. The high level of configurational memory in this rearrangement relies on the steric impediment to the rotation around the C-N bond in the chiral native conformation of the diradical intermediate produced from tandem M-S/1,5-HAT.


Assuntos
Alcadienos/química , Alcinos/química , Ciclização , Modelos Teóricos , Estrutura Molecular , Estereoisomerismo
9.
Angew Chem Int Ed Engl ; 53(12): 3227-31, 2014 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-24554549

RESUMO

An original synthesis of chiral benzofulvenes triggered by organocopper reagents is reported. These enantiopure products are available through a highly chemo-, regio-, diastereo-, and enantioselective bis(alkylating) cycloisomerization process. A double chirality transfer (central-to-axial-to-central) is observed.

10.
J Org Chem ; 78(24): 12566-76, 2013 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-24251782

RESUMO

Allenylzinc formed via oxygen-promoted zinc/iodine exchange between propargyl iodides and diethylzinc can be trapped by intramolecular reaction with various electrophiles such as aldehydes, ketones, esters, carbamates, and imides. Potentially useful building blocks were obtained in high yields.

11.
Colloids Surf B Biointerfaces ; 112: 513-20, 2013 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-24079941

RESUMO

Two novel enediynes containing an aromatic ring and substituted by two thiol functions as end-groups were designed and studied as functionalizing agent of gold nanoparticles. Phototriggered cyclization of the capping agent under UV-visible irradiation was investigated. Interestingly, the length of the thiol-substituted chain was shown to influence significantly the cyclization rate. Depending on the length of the spacer, either polymerization or simple cyclization of the coating agent was evidenced. The present study underscores the possibility of finely controlling the fate of the coating agent (polymerization/cyclization). Nanocomposites were characterized by UV-visible absorption spectroscopy, dynamic light scattering (DLS) technique and transmission electron microscopy (TEM) measurements. Finally, the ability of the colloidal solutions to induce photoinitiated damages to PcDNA3 supercoiled DNA was evaluated. Interestingly, an increase as high as 50% of the DNA cleavage could be registered when adding enediynes-capped gold nanoparticles to solutions of enediynes. In particular, the enhancement of DNA scission was observed in both thermal and photochemical activation modes.


Assuntos
Clivagem do DNA/efeitos dos fármacos , Enedi-Inos/química , Enedi-Inos/farmacologia , Ouro , Nanopartículas Metálicas/química , Materiais Revestidos Biocompatíveis/química , Coloides , Ciclização/efeitos da radiação , DNA Super-Helicoidal/química , DNA Super-Helicoidal/efeitos dos fármacos , DNA Super-Helicoidal/efeitos da radiação , Enedi-Inos/síntese química , Ligantes , Nanopartículas Metálicas/efeitos da radiação , Nanopartículas Metálicas/ultraestrutura , Microscopia Eletrônica de Transmissão , Estrutura Molecular , Nanocompostos/química , Processos Fotoquímicos , Fotólise
12.
Chem Soc Rev ; 42(21): 8434-66, 2013 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-23921426

RESUMO

Substrates, bearing axial chirality, can cyclize intra- or inter-molecularly with concomitant transfer of axial-to-central chirality to produce at least one stereocenter. In order to satisfy a strict definition of axial-to-central chirality transfer, the initial axial chirality must be lost during the cyclization process. Highly functionalized enantiopure carbocycles and heterocycles were prepared using this strategy. The transformations of configurationally stable substrates take place with high regio- and stereo-selectivity. Selected examples involving allenes, biaryls, arylamides and transient axially chiral short-lived species are discussed. Special attention is focused on the mechanistic rationale of the chirality transfer.


Assuntos
Ácidos Carbocíclicos/química , Compostos Heterocíclicos/química , Ciclização , Estrutura Molecular , Silanos/química , Estereoisomerismo
13.
Chirality ; 25(12): 832-9, 2013 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-23939869

RESUMO

The absolute configurations (AC) of azaheterocylic compounds resulting from the cascade rearrangement of enediynes involving only light atoms were unambiguously assigned by the joint use of vibrational circular dichroism (VCD) and copper radiation single crystal X-ray diffraction (XRD). These AC determinations proved that the rearrangements of enediynes proceeded with memory of chirality and retention of configuration.


Assuntos
Enedi-Inos/química , Isoquinolinas/química , Dicroísmo Circular , Simulação por Computador , Estereoisomerismo , Difração de Raios X
14.
J Org Chem ; 78(4): 1589-603, 2013 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-23311748

RESUMO

Propargyl iodides are good precursors for allenylzincs via reaction with diethylzinc, even in nondegassed medium. These reactions proceed via zinc/iodine exchange. Owing to the previously reported detection of propargyl radical by ESR experiments, in this process a radical mechanism was suspected. Calculations of the C-Zn BDEs in allenyl- and propargylzinc species were performed with the CBS-QB3 method to demonstrate that propargyl radicals could undergo homolytic substitution at zinc. The stabilization of allenylzinc derivatives by chelation, made possible by the selection of appropriate ortho-substituted 3-phenylalkynyl iodides as precursors, was shown to influence the regioselectivity of their addition to aldehydes and ketones. The more stabilized the chelated allenylzinc intermediate, the higher the ratio of homopropargylic alcohols.

16.
Chimia (Aarau) ; 66(6): 435-8, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22871289

RESUMO

The system laccase/mediator/dioxygen is able to trigger radical reactions with radical precursors which are not natural substrates of this enzyme. The radical generation has been accomplished by single electron transfer oxidation of a 1,3-dicarbonyl precursor. The process is exemplified with a radical cascade.


Assuntos
Lacase/metabolismo , Transporte de Elétrons , Radicais Livres/química , Radicais Livres/metabolismo , Lacase/química , Estrutura Molecular , Oxirredução , Oxigênio/química , Oxigênio/metabolismo
17.
J Phys Chem A ; 116(29): 7623-8, 2012 Jul 26.
Artigo em Inglês | MEDLINE | ID: mdl-22724535

RESUMO

The reactions of α-hydroxyl and α-alkoxyl alkyl radicals with methanesulfonyl chloride (MeSO(2)Cl) have been studied by pulse radiolysis at room temperature. The alkyl radicals were produced by ionizing radiation of N(2)O-saturated aqueous solution containing methanol, ethanol, isopropanol, or tetrahydrofuran. The transient optical absorption spectrum consisted of a broad band in the region 280-380 nm with a maximum at 320 nm typical of the MeSO(2)(•) radical. The rate constants in the interval of 1.7 × 10(7)-2.2 × 10(8) M(-1) s(-1) were assigned to an electron-transfer process that leads to MeSO(2)Cl(•-), subsequently decaying into MeSO(2)(•) radical and Cl(-). The rate constants for the addition of CH(3)SO(2)(•) to acrolein and propiolic acid were found to be 4.9 × 10(9) M(-1) s(-1) and 5.9 × 10(7) M(-1) s(-1), respectively, in aqueous solutions and reversible. The reactivity of tosyl radical (p-CH(3)C(6)H(4)SO(2)(•)) toward a series of alkenes bearing various functional groups was also determined by competition kinetics in benzene. The rate constants for the addition of tosyl radical to alkenes vary in a much narrower range than the rate constants for the reverse reaction. The stabilization of the adduct radical substantially contributes to the increase of the rate constant for the addition of tosyl radical to alkenes and, conversely, retards the ß-elimination of tosyl radical.

18.
Chemistry ; 18(11): 3241-7, 2012 Mar 12.
Artigo em Inglês | MEDLINE | ID: mdl-22328494

RESUMO

Phtalimidomethyl iodide and substituted maleimidomethyl iodide were used as radical precursors in dialkylzinc-mediated radical addition to diethyl fumarate. The reactions led stereoselectively to functionalized pyrrolizidines. The radical mechanism was supported by spin-trapping experiments and rationalized by theoretical calculations. Radical additions, on the one hand, and carbozincation followed by transmetalation with copper(I), on the other, were shown to be complementary methods to achieve the formal aminomethylation of activated unsaturated compounds.

19.
J Org Chem ; 77(6): 2773-83, 2012 Mar 16.
Artigo em Inglês | MEDLINE | ID: mdl-22339110

RESUMO

Memory of chirality (MOC) and deuterium-labeling studies were used to demonstrate that the cascade rearrangement of enediyne-connected amino esters 1a and 1b evolved through exclusive 1,5- or 1,6-hydrogen atom transfer, subsequent to 1,3-proton shift and Saito-Myers cyclization, depending on the structure of the starting material. These results were independently confirmed by DFT theoretical calculations performed on model monoradicals. These calculations clearly demonstrate that in the alanine series, 1,5-hydrogen shift is kinetically favored over 1,6-hydrogen shift because of its greater exergonicity. In the valine series, the bulk of the substituent at the nitrogen atom has a major influence on the fate of the reaction. N-Tosylation increases the barrier to 1,5-hydrogen shift to the benefit of 1,6-hydrogen shift. The ready availability of 1,6-hydrogen atom transfer was explored as a potential route for the enantioselective synthesis of naphthoazepines.

20.
Chem Commun (Camb) ; 48(19): 2549-51, 2012 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-22286240

RESUMO

The tandem Crabbé homologation-radical rearrangement of terminal enediynes leads, in a one-pot procedure, to the enantioselective synthesis of six- and seven-membered ring α-aminoesters bearing a quaternary stereocenter based on the phenomenon of memory of chirality.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA
...