RESUMO
A nickel-catalyzed three-component coupling reaction between perfluoroarenes and two molecules of a 1,3-diene in the presence of an alkyl Grignard reagent, which acted as a hydride source, provided 3-perfluoroarylated-1,7-octadienes via 1,3-diene dimerization and subsequent perfluoroarylation upon C-F bond cleavage. The reaction proceeded smoothly in a regioselective manner by simply combining NiCl2 and PPh3 as a catalyst and tolerated various functional groups on the perfluoroarenes. When substituted perfluoroarenes were employed, the reaction selectively occurred at the para-position. Mechanistic studies revealed that an anionic Ni complex, generated upon the reaction of Ni(0) with two molecules of a 1,3-diene and an alkyl Grignard reagent, played an important role in the C-C bond forming step with perfluoroarenes. The C-F bond cleavage was found to be a relatively fast step in the catalytic cycle.
RESUMO
A one step formal [3+2]-annulation protocol for the synthesis of 2,3-disubstituted indolines is described. The in situ generated aryne acts as a two-atom component, and γ-amino-α,ß-unsaturated esters acting as a three-atom component to construct indoline units in a highly regio- and diastereoselective manner with yields ranging from 63 to 80%.
RESUMO
An unprecedented synthesis of novel 3-azido indoles has been developed using I2 and NaN3 in high yields and excellent regioselectivity. The reaction proceeds under metal-free conditions at room temperature. Essentially, an umpolung in reactivity at the C-3 position of indole has been achieved by the activation of indoles with I2.
RESUMO
An efficient annulation strategy involving the reaction of phenolic acetates with acrylates in the presence of [Rh2(OAc)4] as catalyst and formic acid as reducing agent, leading to the high yield synthesis of coumarin derivatives, has been developed. The addition of NaOAc as a base increased the yield of the products. The reaction is quite successful for both electron-rich as well as electron-deficient phenolic acetates, affording coumarins with excellent regioselectivity, and proceeds via C-H bond activation proven by deuterium incorporation studies.
RESUMO
A highly efficient one-pot [4 + 1]-annulation process for the asymmetric synthesis of densely functionalized pyrrolidine derivatives is described. The in situ generated syn-Mannich adduct obtained via proline catalysis acts as a four-atom component, and Corey's sulfur ylide or ethyl bromoacetate acts as a one-atom carbon source to construct pyrrolidine units in a highly enantio- and diastereoselective manner.
Assuntos
Prolina/química , Pirrolidinas/química , Aldeídos/química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
An efficient catalytic route for the synthesis of α,ß-unsaturated nitriles from easily accessible gem-dibromoolefins has been developed. The method utilized inexpensive reagents such as Cu2O as a catalyst, L-proline as a ligand and NaCN as a cyanide source to afford α,ß-unsaturated nitriles in high yields (62-86%). A deuterium exchange study has shown that one of the bromide atoms of gem-dibromoolefins exchanges with cyanide while the other with a deuterium atom.
Assuntos
Alcenos/síntese química , Cobre/química , Nitrilas/síntese química , Alcenos/química , Catálise , Cianetos/química , Halogenação , Nitrilas/química , Prolina/química , EstereoisomerismoRESUMO
The investigation of new oxidative transformations for the synthesis of carbon-heteroatom and heteroatom-heteroatom bonds is of fundamental importance in the synthesis of numerous bioactive molecules and fine chemicals. In this context, NaIO4, an exciting reagent, has attracted increasing attention enabling the development of these unprecedented oxidative transformations that are difficult to achieve otherwise. Thus, NaIO4 has been successfully explored as a versatile oxidant for a variety of fundamental organic transformations such as C-H activation, oxidative functionalization of alkenes and other interesting oxidative transformations and its application in the synthesis of bioactive natural products. This review summarizes recent developments in this area with NaIO4 as a versatile oxidant and brings out many challenges that still remain elusive for the future.
RESUMO
A novel, N-heterocyclic carbene (NHC) catalyzed direct oxidative coupling of styrenes with aldehydes has been described for the synthesis of α,ß-epoxy ketones in good yields. This unprecedented regioselective oxidative coupling employs NBS/DBU/DMSO (DBU=1,8-diazabicyclo [5.4. 0] undec-7-ene, DMSO=dimethylsulfoxide, NBS=N-bromosuccinimide) as an oxidative system at ambient conditions. Additionally, first NHC-catalyzed Darzens reaction of α-bromoketones and aldehydes under mild reaction conditions has also been described. Interestingly, mechanistic studies have revealed the preferred reactivity of NHC with alkene/α-bromoketone rather than aldehydes, thus proceeding via the ketodeoxy Breslow intermediate.
RESUMO
The salen Co(III)-catalyzed phenolic kinetic resolution of racemic anti- or syn-azido and benzyloxy epoxides provides a practical route to a range of enantioenriched anti- or syn-1-aryloxy-3-azido or benzyloxy-2-alcohols in excellent yields and ees. The synthetic potential of this protocol is illustrated with an enantioselective synthesis of ICI-118,551, a ß-blocker, in a highly optically pure form (99% ee).
Assuntos
Cobalto/química , Compostos de Epóxi/química , Etilenodiaminas/química , Compostos Organometálicos/química , Fenóis/química , Propanolaminas/química , Propanolaminas/síntese química , Anti-Hipertensivos/síntese química , Anti-Hipertensivos/química , Catálise , Técnicas de Química Sintética , Cinética , EstereoisomerismoRESUMO
A new method of CuCN-mediated one-pot cyclization of 4-(2-bromophenyl)-2-butenoates leading to efficient synthesis of substituted naphthalene amino esters including phenanthrene aromatic structural units is described. Deuterium labeling studies establish that this one-pot cascade cyclization proceeds through isomerization of olefin, intramolecular C-C bond cyclization, and aromatization as the key intermediates, all occurring in a single step.
Assuntos
Cobre/química , Cianetos/química , Ésteres/síntese química , Naftalenos/síntese química , Fenilbutiratos/química , Ciclização , Ésteres/química , Estrutura Molecular , Naftalenos/químicaRESUMO
An N-heterocyclic carbene (NHC)-catalyzed reaction of alkenes with aromatic aldehydes providing for a high yield synthesis of α-acyloxy ketones and esters has been described. This unprecedented regioselective oxidative process employs NBS and Et3N in stoichiometric amounts and O2 (1 atm) as an oxidant under ambient conditions in DMSO as a solvent.
Assuntos
Aldeídos/química , Alcenos/química , Ésteres/síntese química , Compostos Heterocíclicos/química , Cetonas/síntese química , Metano/análogos & derivados , Catálise , Ésteres/química , Cetonas/química , Metano/química , Estrutura Molecular , Oxigênio/química , EstereoisomerismoRESUMO
The HKR of racemic anti- or syn-3-substituted epoxy esters catalyzed by a Co(III)salen complex provides ready access to the corresponding enantioenriched 3,4-disubstituted γ-butyrolactones and 3-substituted epoxy esters. This strategy has been successfully employed in the formal synthesis of biologically active 3,4-disubstituted piperidine derivatives, (-)-paroxetine and Ro 67-8867 and a natural product, (+)-eldanolide.
Assuntos
4-Butirolactona/química , Alcadienos/síntese química , Compostos de Epóxi/química , Ésteres/química , Paroxetina/síntese química , Piperidinas/síntese química , 4-Butirolactona/análogos & derivados , Alcadienos/química , Catálise , Hidrólise , Cinética , Estrutura Molecular , Fenômenos Ópticos , Compostos Organometálicos/química , Paroxetina/química , Piperidinas/química , EstereoisomerismoRESUMO
A new sequential organocatalytic method for the synthesis of chiral 3-substituted (X = OH, NH2) tetrahydroquinoline derivatives (THQs) [ee up to 99%, yield up to 87%] based on α-aminooxylation or -amination followed by reductive cyclization of o-nitrohydrocinnamaldehydes has been described. This methodology has been efficiently demonstrated in the synthesis of two important bioactive molecules namely (-)-sumanirole (96% ee) and 1-[(S)-3-(dimethylamino)-3,4-dihydro-6,7-dimethoxy-quinolin-1(2H)-yl]propanone (92% ee).
Assuntos
Prolina/química , Quinolinas/síntese química , Aldeídos/química , Aminação , Catálise , Ciclização , Oxirredução , Quinolinas/química , EstereoisomerismoRESUMO
The asymmetric dihydroxylation (AD) of o-cyano cinnamates and styrene derivatives leads to efficient construction of chiral phthalide frameworks in high optical purities. This unique reaction is characterized by unusual synergism between CN and osmate groups resulting in rate enhancement of the AD process. The method is amply demonstrated by the synthesis and the structural/stereochemical assignment of the natural products.
Assuntos
Benzofuranos/síntese química , Cinamatos/química , Nitrilas/química , Estirenos/química , Benzofuranos/química , Ciclização , Estrutura Molecular , OxirreduçãoRESUMO
A new enantioselective synthesis of the anti-influenza agent (-)-oseltamivir free base (7.1% overall yield; 98% ee) and (-)-methyl 3-epi-shikimate (16% overall yield; 98% ee) has been described from readily available raw materials. Sharpless asymmetric epoxidation and diastereoselective Barbier allylation of an aldehyde are the key reactions employed in the incorporation of chirality, while the cyclohexene carboxylic ester core was constructed through a ring closing metathesis reaction.
Assuntos
Antivirais/síntese química , Oseltamivir/síntese química , Ácido Chiquímico/análogos & derivados , Catálise , Hidrogenação , Estrutura Molecular , Oxirredução , Ácido Chiquímico/síntese químicaRESUMO
We describe a simple and highly efficient procedure for the single-step preparation of isatins from the commercially available anilines using H-ß zeolite as a truly heterogeneous catalyst. H-ß zeolite is readily separated from reaction mixture by simple filtration and reused several times without considerable loss of activity.
RESUMO
A novel and highly enantioselective method for the synthesis of gamma-amino-alpha,beta-unsaturated esters via tandem alpha-amination-Horner-Wadsworth-Emmons (HWE) olefination of aldehydes is described. The one-pot assembly has been demonstrated for the construction of functionalized chiral 2-pyrrolidones, subunits present in several alkaloids. [structure: see text]
Assuntos
Aldeídos/química , Alcenos/química , Aminas/química , Ésteres/síntese química , Pirrolidinonas/síntese química , Alcaloides/química , Catálise , Técnicas de Química Combinatória , Ciclização , Estrutura Molecular , EstereoisomerismoRESUMO
An unprecedented conversion of alkenes and enol ethers to the corresponding α-imido carbonyl compounds with excellent regioselectivity and yields has been developed. This oxo-amination process employs readily available N-bromosuccinimide (NBS) and secondary amines as N-sources and dimethyl sulfoxide (DMSO) as the oxidant and also leads to the production of amino alcohols in a single step on reduction, thus broadening the scope of this operationally simple reaction. For the first time, the formation of reactive Me2S(+)-O-Br species generated by the interaction of NBS with DMSO has been proven.
Assuntos
Alcenos/química , Bromosuccinimida/química , Aminação , Aminas/química , Amino Álcoois , Catálise , Dimetil Sulfóxido/química , Ésteres , Éteres/síntese química , Éteres/química , Cetonas/síntese química , Cetonas/química , Estrutura Molecular , EstereoisomerismoRESUMO
A novel palladium-catalyzed hydration-olefin insertion cascade assisted by internal nucleophiles was developed for the synthesis of biologically significant 2,3-dihydro-1H-inden-1-ones under mild conditions. A detailed mechanistic study revealed that the assistance of the internal nucleophiles is crucial to trigger the cascade reaction via nucleopalladation of the alkyne moiety. The overall reaction is equivalent to regioselective hydration of alkynes followed by intramolecular Michael addition. This highly efficient and 100% atom-economical domino sequence afforded cis-2,3-disubstituted 2,3-dihydro-1H-inden-1-ones in excellent yields (up to 99%) with complete diastereoselectivity.
RESUMO
N-Bromosuccinimide efficiently catalyzes the hydroamination and hydroalkoxylation of activated styrenes using tosylamides, carbamates, and alcohols as the nucleophiles to afford amino and ether derivatives, respectively. Both the processes give good to excellent yields of the products with 100% regioselectivity (Markovnikov fashion). [structure: see text]