RESUMO
Regioselective arylation of carbazoles is reported using dual palladium-photoredox catalysis. Controlled monoarylation and diarylation of symmetrical and unsymmetrical carbazoles were achieved under mild reaction conditions with a broad substrate scope and functional group tolerance. Steric and electronic control the regioselectivity of the arylation of unsymmetrical carbazoles. Late-stage functionalization of a caprofen drug derivative and large-scale synthesis of mono- and di-arylated carbazoles were demonstrated to showcase the synthetic versatility of the method. Finally, we also showcased the synthesis of hyellazole analogues (a marine alkaloid) in a short route using our strategy.
RESUMO
We have described a dual palladium-photoredox-catalyzed highly regioselective acylation of carbazoles and indolines using molecular oxygen as the green oxidant. The reaction shows a broad substrate scope and good functional group tolerance. Late-stage functionalization of a carprofen drug derivative, further manipulation of products, and gram-scale synthesis of the acylated products were illustrated to show the versatility of the method.
RESUMO
Photoredox-mediated tandem addition-chemoselective cyclization of o-alkenyl aryl ureas is reported for the synthesis of sulfonyl and activated alkyl-decorated dihydroquinazolinones. By a careful choice of o-alkenyl aryl urea starting materials, we achieved chemoselective N-cyclization in the presence of more reactive amidic oxygen. We have demonstrated the scope of the methodology with a variety of sulfonyl chlorides and activated alkyl halides. Finally, large-scale synthesis of sulfonyl-substituted dihydroquinazolinone showcases the synthetic utility of the methodology.
Assuntos
Amidas , Ureia , Catálise , CiclizaçãoRESUMO
Biphenylyl/thiophene systems are known for their ambipolar behavior and good optical emissivity. However, often these systems alone are not enough to fabricate the commercial-grade light-emitting devices. In particular, our recent experimental and theoretical analyses on the three-ring-constituting thiophenes end capped with biphenylyl have shown good electrical properties but lack of good optical properties. From a materials science perspective, one way to improve the properties is to modify their structure and integrate it with additional moieties. In recent years, furan moieties have proven to be a potential substitution for thiophene to improve the organic semiconductive materials properties. In the present work, we systematically substituted different proportions of furan rings in the biphenylyl/thiophene core and studied their optoelectronic properties, aiming toward organic light-emitting transistor applications. We have found that the molecular planarity plays a vital role on the optoelectronic properties of the system. The lower electronegativity of the O atom offers better optical properties in the furan-substituted systems. Further, the furan substitution significantly affects the molecular planarity, which in turn affects the system mobility. As a result, we observed drastic changes in the optoelectronic properties of two furan-substituted systems. Interestingly, addition of furan has reduced the electron mobility by one fold compared to the pristine thiophene-based derivative. Such a variation is interpreted to be due to the low average electronic coupling in furan systems. Overall, systems with all furan and one ring of furan in the center end capped with thiophene have shown better optoelectronic properties. This molecular architecture favors more planarity in the system with good electrical properties and transition dipole moments, which would both play a vital role in the construction of an organic light-emitting transistor.
RESUMO
Derivatives of ribosyl pyrophosphate have been synthesized, and examined with magnesium salts in the coupling of the ribose unit to various nucleophiles, including pyrazole and 2-chloroimidazole. Only with the magnesium salt present did they generate the ribosyl cation by binding to the leaving group and then couple the ribose derivative with nucleophiles. The role of magnesium salts in phosphorylation of methanol by ATP was also examined. Here a remarkable effect was seen: phosphorylation by ATP was slowed with low concentrations of Mg(2+) but accelerated by higher concentrations. Related effects were also seen in the effect of Mg(2+) on phosphorylation by ADP. The likely mechanisms explain these effects.
Assuntos
Trifosfato de Adenosina/metabolismo , Difosfatos/metabolismo , Compostos de Magnésio/metabolismo , Mimetismo Molecular , Nucleotídeos/biossíntese , Origem da Vida , Fosforilação/fisiologia , Metanol/metabolismo , Estrutura Molecular , Ribose/metabolismoRESUMO
We herein report the Rh(III) catalyzed redox-neutral C-H activation/[5 + 2] annulation of aroyl hydrazides with sulfoxonium ylides as safe carbene precursors. The reaction shows excellent functional group tolerance, broad substrate scope, and scalability. We demonstrated the synthetic utility of the protocol via the synthesis of various diazepam drug analogues, late-stage functionalization of probenecid drug, and large scale synthesis. Finally, kinetic studies revealed C-H activation as the rate-determining step.
RESUMO
We describe a simple and convenient synthesis of the western zone of caprazamycin B using two catalytic asymmetric reactions as key elements of our approach. Desymmetrization of 3-methylglutaric anhydride with the (S)-Ni(2)-(Schiff base) complex as a catalyst furnished the chiral hemiester, and a thioamide-aldol reaction with mesitylcopper, (R,R)-Ph-BPE, and 2,2,5,7,8-pentamethylchromanol as a catalyst furnished the ß-hydroxy thioamide in good yield and enantioselectivity. On further transformation, the thioamide functionality was converted to the corresponding ß-hydroxy ester. Finally, a convergent synthesis of the western zone of caprazamycin B was achieved by connecting the hemiester, the ß-hydroxy ester, and the 2,3,4-tri-O-methyl-l-rhamnose fragments.
Assuntos
Lipídeos/síntese química , Nucleosídeos/síntese química , Catálise , Lipídeos/química , Estrutura Molecular , Nucleosídeos/química , EstereoisomerismoRESUMO
Organoselenium compounds have attracted intense research owing to their unique biological properties as well as pharmaceutical significance. Progress has been made in developing reagents for incorporation of selenium in an efficient and controlled manner. Herein, we present a review on the recently developed selenium reagent, tetraethylammonium tetraselenotungstate, [Et(4)N](2)WSe(4) as a versatile selenium transfer reagent in organic synthesis. Tetraselenotungstate has been successfully used for the synthesis of a number of functionalized diselenides, sugar- and nucleoside-derived diselenides, seleno-cystines, selenohomocystines, selenoamides, selenoureas and sugar- and nucleoside-based cyclic-selenide derivatives. Additionally, this reagent has been employed for the ring opening of aziridines to synthesize a variety of ß-aminodiselenides. A new selena-aza-Payne type rearrangement of aziridinemethanoltosylates mediated by tetraselenotungstate for the synthesis of allyl amines is also discussed.
Assuntos
Compostos Organosselênicos/síntese química , Aminas/síntese química , Aminas/química , Estrutura Molecular , Compostos Organosselênicos/químicaRESUMO
Herein, we report a substrate-controlled cascade cyclization of o-alkenyl aryl ureas, an ambident nucleophile for constructing functionalized heterocycles such as 2-amino-1,3-benzoxazines and dihydroquinazolinones in a chemodivergent fashion using photoredox catalysis under mild conditions. The versatility of the method has been successfully demonstrated by applying this strategy to a wide range of substrates and for the synthesis of functionalized etifoxine drug derivatives.
RESUMO
We herein report hydrazine-directed, Rh(III) catalyzed (4+2) annulation of N-alkyl aryl hydrazines with sulfoxonium ylides as a safe carbene precursor. The reaction shows excellent functional group tolerance with broad substrate scope, scalability and site selectivity. Finally, photophysical studies indicated that some of these compounds have interesting fluorescence properties.
Assuntos
Ródio , Catálise , Hidrazinas , Estrutura Molecular , Ródio/químicaRESUMO
A number of doubly activated cyclopropanes were synthesized starting from various substituted bromosulfonium bromides in good yield. Regioselective ring-opening of cyclopropanes with tetrathiomolybdate as the sulfur transfer reagent gave dihydrothiophenes in excellent yield.
Assuntos
Ciclopropanos/química , Ciclopropanos/síntese química , Indicadores e Reagentes/química , Molibdênio/química , Compostos de Sulfônio/química , Compostos de Sulfônio/síntese química , Enxofre/química , Tiofenos/química , Tiofenos/síntese química , Espectroscopia de Ressonância Magnética , Estrutura Molecular , EstereoisomerismoRESUMO
Mandelic acids represent a key structural motif present in many drug molecules. Herein, we report the controlled meta-selective mono- and diolefination of mandelic acids by the careful design of the substrate and oxidant. Furthermore, free meta-functionalized mandelic acid was generated by selectively removing the template under mild basic conditions. The synthesis of functionalized homatropine and cyclandelate drug derivatives was demonstrated. Kinetic isotope effects revealed C-H activation as the rate-limiting step.
RESUMO
A highly chemoselective C-H arylation of phenylureas has been accomplished using dual palladium-photoredox catalysis at room temperature without any additives, base or external oxidants. Regioselective C-H arylation of N,N'-diaryl substituted unsymmetrical phenylureas has also been accomplished by a careful choice of aryl groups.
Assuntos
Paládio/química , Compostos de Fenilureia/química , Catálise , Luz , Oxirredução , Paládio/efeitos da radiaçãoRESUMO
An efficient protocol is reported for the synthesis of thioesters from carboxylic acids with use of acyloxy phosphonium salts as intermediates and benzyltriethylammonium tetrathiomolybdate as the sulfur transfer reagent.
Assuntos
Ácidos Carboxílicos/química , Molibdênio/química , Compostos Organofosforados/química , Compostos de Amônio Quaternário/química , Enxofre/química , Ésteres , Indicadores e Reagentes/químicaRESUMO
Catalytic asymmetric total synthesis of caprazol, a lipo-nucleoside antibiotic, has been accomplished employing two of the stereoselective C-C bond forming reactions as key transformations. The stereochemistries of the ß-hydroxy-α-aminoester moiety at the juncture of the uridine part and diazepanone part, and of the ß-hydroxy-α-amino acid moiety embedded in the diazepanone system, were constructed using a diastereoselective isocyanoacetate aldol reaction (dr = 88:12) and an enantioselective anti-nitroaldol reaction catalyzed by a Nd/Na-chiral amide ligand (dr = 12:1, 95% ee), respectively.
Assuntos
Antibacterianos/síntese química , Azepinas/síntese química , Uridina/análogos & derivados , Aldeídos/química , Aminoácidos/síntese química , Aminoácidos/química , Antibacterianos/química , Antibacterianos/farmacologia , Azepinas/química , Azepinas/farmacologia , Catálise , Estrutura Molecular , Nucleosídeos/química , Estereoisomerismo , Uridina/síntese química , Uridina/química , Uridina/farmacologiaRESUMO
We describe the desymmetrization of meso-glutaric anhydrides to chiral hemiesters using a bench-stable homodinuclear Ni(2)-(Schiff base) complex as the catalyst in good to excellent yield (up to 99%) and enantioselectivity (up to 94%). Using the opposite enantiomer of the catalyst, we obtained the same yield and enantioselectivity with the opposite configuration, thereby gaining access to both hemiester enantiomers.