RESUMO
This work describes a novel and practical method for the Cu-catalyzed C(sp3)-C(sp2) cross-coupling of alkylsilyl peroxides with arylboronic acids. The reductive cleavage of the O-O bond of alkylsilyl peroxides and the desired cross-coupling reactions to afford alkyl-substituted aromatic rings proceed smoothly at room temperature promoted by simple Cu-based catalysts and do not require activation by visible light. The results of mechanistic investigations support a radical-mediated C(sp3)-C(sp2) bond formation via ß-scission of the alkoxy radicals generated from the alkylsilyl peroxides.
RESUMO
This article describes a variety of 3,3-disubstituted 2-oxindoles that bear carbonyl groups, which are efficiently obtained from a radical reaction between N-arylacrylamides and aliphatic aldehydes. The reaction is initiated by the photolysis of hypervalent iodine(iii) reagents and proceeds smoothly under mild, metal-free conditions.
RESUMO
The copper-catalyzed selective mono-N-alkylation of primary amides or arylamines using alkylsilyl peroxides as alkylating agents is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the alkylsilyl peroxides, as well as to the primary amides and arylamines. Mechanistic studies suggest that the present reaction should proceed through a free-radical process that includes alkyl radicals generated from the alkylsilyl peroxides.
RESUMO
Diastereoselective radical hydroacylation of chiral alkylidenemalonates with aliphatic aldehydes is realized by the combination of a hypervalent iodine(III) reagent and UV-light irradiation. The reaction is initiated by the photolysis of hypervalent iodine(III) reagents under mild, metal-free conditions, and is the first example of diastereoselective addition of acyl radicals to olefins to afford chiral ketones in a highly stereoselective fashion. The obtained optically active ketones are useful chiral synthons, as exemplified by the short formal synthesis of (-)-methyleneolactocin.
Assuntos
Aldeídos/química , Indicadores e Reagentes/química , Iodo/química , Lactonas/síntese química , Catálise , Lactonas/química , Estrutura Molecular , FotóliseRESUMO
This article describes an efficient method for the introduction of perfluoroalkyl groups into N-acrylamides, 2-isocyanides, olefins, and other heterocycles using perfluoroalkyl radicals that were generated from the reaction between sodium perfluoroalkanesulfinates and a hypervalent iodine(iii) reagent. This approach represents a simple, scalable perfluoroalkylation method under mild and metal-free conditions.
RESUMO
A facile synthetic route to a 3-bromo binaphthyl-based secondary amine through the monobromination of an axially chiral dicarboxylic acid derivative has been developed. The combination of this new procedure with coupling reactions established an efficient synthetic approach to a series of binaphthyl-based secondary amine catalysts containing various functional groups in an efficient way.
RESUMO
An asymmetric synthesis of cyclic amino acids having piperidine and azepane core structures was realized starting from readily available glycine and alanine esters by combination of phase-transfer catalyzed asymmetric alkylation and subsequent reductive amination.
Assuntos
Aminoácidos Cíclicos/química , Aminoácidos Cíclicos/síntese química , Química Orgânica/métodos , Transição de Fase , Alquilação , Aminação , Catálise , Ésteres/síntese química , Ésteres/química , EstereoisomerismoRESUMO
The 1,2-diamine (vicinal diamine) motif is present in a number of natural products with interesting biological activity and in many chiral molecular catalysts. The efficient and stereocontrolled synthesis of enantioenriched vicinal diamines is still a challenge to modern chemical methodology. We report here both syn- and anti-selective asymmetric direct Mannich reactions of N-protected aminoacetaldehydes with N-Boc-protected imines catalyzed by proline and the axially chiral amino sulfonamide (S)-3. This organocatalytic process represents the first example of a Mannich reaction using Z- or Boc-protected aminoacetaldehyde as a new entry of α-nitrogen functionalized aldehyde nucleophile in enamine catalysis. The obtained optically active vicinal diamines are useful chiral synthons as exemplified by the formal synthesis of (-)-agelastatin A.
Assuntos
Acetaldeído/química , Alcaloides/síntese química , Diaminas/síntese química , Oxazolidinonas/síntese química , Acetaldeído/síntese química , Alcaloides/química , Catálise , Diaminas/química , Iminas/síntese química , Iminas/química , Modelos Moleculares , Oxazolidinonas/química , Prolina/síntese química , Prolina/química , EstereoisomerismoRESUMO
This article describes the synthetic application of ketone-derived oxaziridines as alkyl radical precursors in copper-catalyzed Carbon-Carbon bond formation reactions. Experimental and computational studies indicate a free radical mechanism, where alkyl radicals are efficiently generated via cleavage of a Carbon-Carbon bond of oxaziridines. Acyclic and unstrained cyclic oxaziridines are applicable to the present radical process, allowing for the generation of various alkyl radicals with good functional group compatibility.
RESUMO
A novel radical-based approach for the iron-catalyzed selective cleavage of acetal-derived alkylsilyl peroxides, followed by the formation of a carbon-carbon bond is reported. The reaction proceeds under mild reaction conditions and exhibits a broad substrate scope with respect to the acetal moiety and the carbon electrophile. Mechanistic studies suggest that the present reaction proceeds through a free-radical process involving carbon radicals generated by the homolytic cleavage of a carbon-carbon bond within the acetal moiety. A synthetic application of this method to sugar-derived alkylsilyl peroxides is also described.
RESUMO
Methods for direct functionalization of C-H bonds mediated by N-oxyl radicals constitute a powerful tool in modern organic synthesis. While several N-oxyl radicals have been developed to date, the lack of structural diversity for these species has hampered further progress in this field. Here we designed a novel class of N-oxyl radicals based on N-hydroxybenzimidazole, and applied them to the direct C-H functionalization reactions. The flexibly modifiable features of these structures enabled facile tuning of their catalytic performance. Moreover, with these organoradicals, we have developed a metal-free approach for the synthesis of acyl fluorides via direct C-H fluorination of aldehydes under mild conditions.
RESUMO
The facile synthesis of functionalized organoboron/silicon compounds by copper-catalyzed coupling of alkylsilyl peroxides and diboron/silylborane reagents is reported. The reactions proceed smoothly under mild, neutral conditions in short reaction times to generate organoboron/silicon compounds bearing a ketone moiety, which are useful synthetic intermediates that are otherwise difficult to access. The results of mechanistic investigations suggest the radical-mediated formation of carbon-boron and carbon-silicon bonds via ß-scission of alkoxy radicals.
RESUMO
The synthesis of sodium α-aminoalkanesulfinates and their synthetic utility as α-aminoalkyl radical precursors are reported. A variety of α-aminoalkanesulfinates were readily obtained from the reaction between the anions of N-Boc-protected alkylamines and 1,4-diazabicyclo[2.2.2]octanebis(sulfur dioxide). Treatment of sodium α-aminoalkanesulfinates with (diacetoxyiodo)benzene easily generated the corresponding α-aminoalkyl radicals under mild conditions, which were then applied in radical 1,2-addition to imines, radical 1,4-addition to electron-deficient olefins, and radical addition/cyclization to 2-isocyanobiphenyls.
RESUMO
A copper-catalyzed C(sp)-C(sp3) coupling reaction between terminal alkynes and alkylsilyl peroxides is reported. In the presence of a copper catalyst and 4-dimethylaminopyridine, the reaction smoothly affords a variety of internal alkynes by coupling alkylsilyl peroxides and terminal alkynes. Mechanistic studies suggest that the reaction proceeds via a radical mechanism, whereby the alkyl radicals are generated from the alkylsilyl peroxides. The present transformation represents a rare example of a radical-mediated C(sp)-C(sp3) coupling reaction of terminal alkynes.
RESUMO
The copper-catalyzed selective mono-N-alkylation of primary amides with bis(trialkylsilyl) peroxides as alkylating agents was reported. The results of a mechanistic study suggest that this reaction should proceed via a free radical process that includes the generation of alkyl radicals from bis(trialkylsilyl) peroxides.
RESUMO
In this letter, an efficient method for the photolytic generation of difluoromethyl radicals from [bis(difluoroacetoxy)iodo]benzene reagents is described. The present approach enables the introduction of difluoromethyl groups into various heteroarenes under mild conditions in the absence of any additional reagents or catalysts.
RESUMO
In contrast to the well-known [2 + 2] photocycloadditions between CâO and CâC bonds, the participation of CâN bonds in such reactions is relatively rare. In this paper, the unprecedented UV-light-induced [2 + 2] cycloadditions between N-arylsulfonylimines and styrene derivatives or benzofurans are described. This photolytic reaction allows the highly stereoselective construction of azetidine derivatives under ambient conditions.
RESUMO
A practical approach to radical C-H bond functionalization by the photolysis of a hypervalent iodine(iii) reagent is presented. The photolysis of [bis(trifluoroacetoxy)iodo]benzene (PIFA) leads to the generation of trifluoroacetoxy radicals, which allows the smooth transformation of various alkylbenzenes to the corresponding benzyl ester compounds under mild reaction conditions.
Assuntos
Benzeno/química , Indicadores e Reagentes/química , Iodo/química , FotóliseRESUMO
Egg-drop syndrome (EDS) virus is an avian adenovirus that causes a sudden drop in egg production and in the quality of the eggs when it infects chickens, leading to substantial economic losses in the poultry industry. Inactivated EDS vaccines produced in embryonated duck eggs or cell culture systems are available for the prophylaxis of EDS. However, recombinant subunit vaccines that are efficacious and inexpensive are a desirable alternative. In this study, we engineered chimeric fusion proteins in which the trimeric fiber knob domain lacking the triple ß-spiral motif in the fiber shaft region was genetically fused to trimeric coiled coils, such as those of the engineered form of the GCN4 leucine zipper peptide or chicken cartilage matrix protein (CMP). The fusion proteins were expressed predominantly as soluble trimeric proteins in Escherichia coli at levels of 15-80mg/L of bacterial culture. The single immunization of chickens with the purified fusion proteins, at a dose equivalent to 10µg of the knob moiety, elicited serum antibodies with high hemagglutination inhibition (HI) activities, similar to those induced by an inactivated EDS vaccine. A dose-response analysis indicated that a single immunization with as little as 1µg of the knob moiety of the CMP-knob fusion protein was as effective as the inactivated vaccine in inducing antibodies with HI activity. The immunization of laying hens had no apparent adverse effects on egg production and effectively prevented clinical symptoms of EDS when the chickens were challenged with pathogenic EDS virus. This study demonstrates that the knob domain lacking the shaft sequence but fused to a trimeric coiled coil is a promising candidate subunit vaccine for the prophylaxis of EDS in chickens.
Assuntos
Infecções por Adenoviridae/veterinária , Proteínas do Capsídeo/imunologia , Galinhas/imunologia , Doenças das Aves Domésticas/prevenção & controle , Vacinas Virais/imunologia , Infecções por Adenoviridae/prevenção & controle , Animais , Anticorpos Antivirais/sangue , Aviadenovirus , Ovos , Feminino , Testes de Inibição da Hemaglutinação , Doenças das Aves Domésticas/virologia , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/imunologia , Vacinas de Subunidades Antigênicas/imunologia , Vacinas Sintéticas/imunologiaRESUMO
In this communication, we present a regioselectivity switch for the chiral amine-catalysed asymmetric addition of aldehydes to reactive enals to afford either aldol adducts or conjugate adducts in a stereoselective fashion. The unprecedented asymmetric aldol reaction of aldehydes with enals was realized by the use of a diarylprolinol catalyst, giving synthetically useful and important chiral allylic alcohols.