Your browser doesn't support javascript.
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 225
Filtrar
Mais filtros










Base de dados
Intervalo de ano de publicação
1.
J Org Chem ; 2020 May 26.
Artigo em Inglês | MEDLINE | ID: mdl-32441100

RESUMO

This study reports a new application area of difluoro enol silyl ethers, which can be easily obtained from trifluoromethyl ketones. The main focus has been directed to the electrophilic fluoroalkylation and arylation methods. The trifluoromethylthiolation of difluoro enol silyl ethers can be used for the construction of a novel trifluoromethylthio-α,α-difluoroketone (-COCF2SCF3) functionality. The -CF2SCF3 moiety has interesting properties due to the electron-withdrawing, albeit lipophilic, character of the SCF3 group, which can be combined with the high electrophilicity of the difluoroketone motif. The methodology could also be extended to difluoro homologation of the trifluoromethyl ketones using the Togni reagent. In addition, we presented a method for transition-metal-free arylation of difluoro enol silyl ethers based on hypervalent iodines.

2.
Chem Commun (Camb) ; 55(89): 13358-13361, 2019 Nov 18.
Artigo em Inglês | MEDLINE | ID: mdl-31625541

RESUMO

Geminal 18F-oxyfluorination of diazoketones was performed in the presence of rhodium mediators. The reactions were performed using a hypervalent iodine-based [18F]fluoro-benziodoxole reagent. By this methodology various α-[18F]fluoro ethers were obtained in high radiochemical yield (up to 98%) and molar activity (216 GBq µmol-1).

3.
Chem Sci ; 10(23): 5990-5995, 2019 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-31360406

RESUMO

A new Zn-mediated trifluoromethylthiolation-based bifunctionalization reaction is developed. In this process, simultaneous C-SCF3 and C-C bond formation takes place in a multicomponent reaction, in which an aryl and a SCF3 group arise from different reagents. Our studies show that the reaction mechanism is similar to the Hooz multicomponent coupling. The process involves in situ generation of BAr3, which reacts with a diazocarbonyl compound, and the reaction is terminated by an electrophilic SCF3 transfer. The reaction can also be extended to fluorination based bifunctionalization which proceeds with somewhat lower yield than the analogous trifluoromethylthiolation reaction.

4.
Arch Suicide Res ; 23(4): 662-677, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30152725

RESUMO

The relationship between suicide and social class has proved to be complex. Durkheim predicted suicide rates would increase with social status, while others thought the opposite. Results have been mixed. In some studies, suicidality has increased with increasing social status, and in other studies, the two variables have had an inverse relationship. These studies have been primarily conducted on general non-psychiatric populations The present study, in contrast, examines this relationship on a 20-year prospective longitudinal sample of 400 psychiatric patients (differentiated by psychiatric diagnosis) after index hospitalization. Of these, 160 patients show some sign of suicide risk (87 cases of suicidal ideation, 41 of suicide attempts, and 32 suicide completions). A complicated pattern emerges across psychiatric diagnosis, gender, and race. The great majority of patients show no statistically significant relationship between social status and suicide risk. At the maximally different extremes, however, a dramatic difference does emerge. White women diagnosed with nonpsychotic depression show a positive relationship between social status and suicide risk (p < .01) while black men diagnosed with schizophrenia show a negative relationship between these 2 variables (p < .02). The relationship between social status and suicidality among psychiatric patients varies across race, gender, and psychiatric diagnosis. More research needs to be done on this complex and important topic, especially with regard to samples of psychiatric patients. The role of anomie should be studied.

5.
Org Lett ; 20(21): 6646-6649, 2018 11 02.
Artigo em Inglês | MEDLINE | ID: mdl-30350651

RESUMO

Density functional theory calculations were performed to study the detailed reaction mechanisms of rhodium-catalyzed oxyaminofluorination and oxyaminotrifluoromethylthiolation of diazocarbonyl compounds with electrophilic N-F and N-SCF3-based reagents. The calculations show that the operating mechanisms for the two reactions are identical. The catalytic cycle starts with N2 dissociation to provide a rhodium-carbene intermediate, followed by nucleophilic attack of tetrahydrofuran on the carbene and a rhodium coordination change generating a rhodium-enolate intermediate. Subsequent electrophilic attack introduces the fluorine or the SCF3 moiety, and it is followed by nucleophilic attack of the remaining amino group to yield the final product.

6.
Chem Commun (Camb) ; 54(91): 12852-12855, 2018 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-30375599

RESUMO

A new asymmetric catalytic propargyl- and allylboration of hydrazonoesters is reported. The reactions utilize allenyl- and allylboronic acids in the presence of the inexpensive parent BINOL catalyst. The reactions can be performed under mild conditions (0 °C) without any metal catalyst or other additives affording sterically encumbered chiral α-amino acids. This is the first metal-free method for the asymmetric propargyl- and allylboration of hydrazonoesters.

7.
Chem Sci ; 9(13): 3305-3312, 2018 Apr 07.
Artigo em Inglês | MEDLINE | ID: mdl-29732108

RESUMO

Tri- and tetrasubstituted allenylboronic acids were prepared via a new versatile copper-catalyzed methodology. The densely functionalized allenylboronic acids readily undergo propargylboration reactions with ketones and imines without any additives. Catalytic asymmetric propargylborylation of ketones is demonstrated with high stereoselectivity allowing for the synthesis of highly enantioenriched tertiary homopropargyl alcohols. The reaction is suitable for kinetic resolution of racemic allenylboronic acids affording alkynes with adjacent quaternary stereocenters.

8.
J Org Chem ; 83(15): 8786-8792, 2018 08 03.
Artigo em Inglês | MEDLINE | ID: mdl-29792434

RESUMO

Tosylhydrazones and allenylboronic acids underwent a transition-metal-free reductive coupling reaction. This process is suitable for synthesis of tetra- and pentasubstituted conjugated dienes. The corresponding allenyl-Bpin substrate showed a very poor reactivity. The reaction is suggested to involve coupling of the in situ formed diazo compound and allenylboronic acid. The intermediate formed in this coupling undergoes allenyl migration followed by protodeboronation to furnish a conjugated diene as major product.

9.
Chem Commun (Camb) ; 54(34): 4286-4289, 2018 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-29632936

RESUMO

Operationally simple radiosynthesis and purification of [18F]fluoro-benziodoxole was developed starting from a cyclotron produced [18F]F- precursor, [18F]TBAF, and tosyl-benziodoxole. The synthetic utility of [18F]fluoro-benziodoxole was demonstrated by electrophilic fluorocyclization of o-styrilamides proceeding with high RCC (typically 50-90%) and high molar activity (up to 396 GBq µmol-1).

10.
Org Lett ; 19(24): 6590-6593, 2017 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-29190108

RESUMO

This communication describes an efficient palladium pincer complex-catalyzed allylic C-H borylation of alkenes. The transformation exhibits high regio- and stereoselectivity with a variety of linear alkenes. A synthetically useful feature of this allylic C-H borylation method is that all allyl-Bpin products can be isolated in usually high yields. Preliminary mechanistic studies indicate that this C-H borylation reaction proceeds via Pd(IV) pincer complex intermediates.

11.
Org Lett ; 19(24): 6586-6589, 2017 12 15.
Artigo em Inglês | MEDLINE | ID: mdl-29181971

RESUMO

An efficient methodology for the synthesis of vinyl-, allyl-, and (E)-2-boryl allylboronates from propargylic alcohols via Cu-catalyzed borylation under mild conditions is reported. In the presence of commercially available Cu(OAc)2 or Cu(acac)2 and Xantphos, the reaction affords the desired products in up to 92% yield with a broad substrate scope (43 examples). Isolation of an allenyl boronate as the reaction intermediate suggests that an insertion-elimination-type reaction, followed by borylcupration, is involved in the borylation of propargylic alcohols.

12.
Org Lett ; 19(21): 5904-5907, 2017 11 03.
Artigo em Inglês | MEDLINE | ID: mdl-29039676

RESUMO

Density functional theory calculations have been performed to investigate the binaphthol-catalyzed allylboration of skatoles. The high stereoselectivity observed for the reaction is reproduced well by the calculations and was found to be mainly a result of steric repulsions in the corresponding Zimmerman-Traxler transition states. The role of the additive MeOH in enhancing the stereoselectivity was also investigated and is suggested to promote the formation of less reactive allylboronic ester intermediates, thereby suppressing the formation of allylboroxine species, which undergo the facile racemic background reaction.

13.
Org Lett ; 19(17): 4548-4551, 2017 09 01.
Artigo em Inglês | MEDLINE | ID: mdl-28816049

RESUMO

A new Rh-catalyzed, three-component reaction for the oxytrifluoromethylthiolation of α-diazoketones was developed. The SCF3 functionality was introduced using a stable dibenzenesulfonimide reagent under mild conditions. Alcohols, acetals, and ethers were used as the alkoxy sources. Cyclic ethers underwent a trifunctionalization reaction through the introduction of SCF3, OR, and N(SO2Ph)2 substituents in a single step.

14.
Chem Sci ; 8(2): 1056-1061, 2017 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-28451244

RESUMO

A new method is presented for 1,3-difluorination and 1,3-oxyfluorination reactions. The process is based on iodonium mediated opening of 1,1-disubstituted cyclopropanes. The reaction proceeds with high chemo- and regioselectivity under mild reaction conditions typically at room temperature in a couple of hours. The reaction probably occurs via electrophilic ring-opening of cyclopropanes.

15.
Org Lett ; 19(7): 1622-1625, 2017 04 07.
Artigo em Inglês | MEDLINE | ID: mdl-28334535

RESUMO

In this study, we present the synthesis of new, stereodefined allylboronic acids employed to investigate the stereochemistry of the Cu-catalyzed cross-coupling of allylboronic acids with α-diazoketones. According to our results, this reaction proceeds with retention of the relative configuration of the allylboronic acid substrate. We suggest that the stereoinduction step involves a syn SE2'-type transmetalation of the allylboronic acid substrate with a Cu-carbene species.

16.
Org Lett ; 19(5): 1204-1207, 2017 03 03.
Artigo em Inglês | MEDLINE | ID: mdl-28207271

RESUMO

Alcohols are among the most abundant and readily available organic feedstocks in industrial processes. The direct catalytic functionalization of sp3 C-O bonds of alcohols remains the main challenge in this field. Here, we report a copper-catalyzed synthesis of benzyl-, allyl-, and allenyl-boronates from benzylic, allylic, and propargylic alcohols, respectively. This protocol exhibits a broad reaction scope (40 examples) and high efficiency (up to 95% yield) under mild conditions, including for the preparation of secondary allylic boronates. Preliminarily mechanistic studies suggest that nucleophilic substitution is involved in this reaction.

17.
J Am Chem Soc ; 139(1): 2-14, 2017 01 11.
Artigo em Inglês | MEDLINE | ID: mdl-27966922

RESUMO

In this Perspective we will highlight the most important recent breakthroughs in selective allylboron chemistry (both the synthesis and application of these species). In addition we will provide an outlook toward the future of this promising subfield of organic synthesis.

18.
Chem Commun (Camb) ; 52(97): 13963-13966, 2016 Nov 29.
Artigo em Inglês | MEDLINE | ID: mdl-27844069

RESUMO

Nucleophilic 18F-fluorination of bromodifluoromethyl derivatives was performed using [18F]Bu4NF in the presence of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). This novel procedure provided a diverse set of [18F]trifluoroacetamides in good to excellent radiochemical conversions. A mechanism where DBU acts as organomediator in this transformation is proposed.

19.
Angew Chem Int Ed Engl ; 55(46): 14417-14421, 2016 11 07.
Artigo em Inglês | MEDLINE | ID: mdl-27735124

RESUMO

The catalytic asymmetric allylboration of cyclic imines with γ,γ-disubstituted allylboronic acids provides products with adjacent stereocenters in high yield and stereoselectivity. Various electrophiles, including 3,4-dihydroisoquinolines and indoles, were prenylated in a fully stereodivergent fashion by switching the E/Z geometry of the allylboronate and/or the enantiomer of the BINOL catalyst. 3-Methylindole provided products with three adjacent stereocenters with high stereoselectivity in one synthetic operation.

20.
Org Lett ; 18(10): 2503-6, 2016 05 20.
Artigo em Inglês | MEDLINE | ID: mdl-27166509

RESUMO

Palladium catalyzed cross-coupling of allylboronic acids with α-diazoketones was studied. The reaction selectively affords the linear allylic product. The reaction proceeds with formation of a new C(sp(3))-C(sp(3)) bond. The reaction was performed without an external oxidant, likely without the Pd-catalyst undergoing redox reactions.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA