RESUMO
Chiral spirocyclopropyl ß-lactams are common motifs in bioactive compounds and pharmaceuticals. Here we disclose a diastereoselective and enantioselective hydroborylation and hydrosilylation of spirocyclopropenes, via a Cu-catalyzed desymmetrization strategy, for the rapid preparation of enantio-enriched spirocyclopropyl ß-lactams. The efficient desymmetrization strategy allows the remote control of axial chirality, offering the borylated and silylated products bearing central, spiro, and axial chirality. The combination of multichiral elements would provide a novel motif for biological evaluation in potential drug discovery.
RESUMO
Hydroarylation of alkenes is one of the most straightforward and atom-economical strategy for the construction of multi-aryl-substituted alkanes, but systematic studies have been limited to transition metal catalysis. Here we report a hexafluoroisopropanol (HFIP)-promoted hydroarylation of alkenes with indoles without the presence of transition metal catalysts or any additive. HFIP was the only reagent used in this work, and could be easily removed via evaporation, and recovered via distillation in industry settings. This reaction was shown to provide an efficient, clean and operationally simple procedure with a remarkable substrate scope and versatile transformations, delivering a variety of multi-aryl alkanes incorporating the indole motif. In preliminary studies, several of these products showed biologically activity against cells from an array of human cancer cell lines. A mechanistic study was also carried out and suggested that the quinone methide might be the key intermediate. And in contrast to the conclusions of a previous report, the current work suggested that protonation by HFIP might not be the rate-determining step.
RESUMO
An effective (NHC)AgCl catalysis was developed in the hydroborylation of cyclopropenes with B2pin2, delivering a variety of cyclopylboronates in a stereoselective manner, which could be easily transformed for the construction of versatile cyclopropanes. This protocol works effectively under mild reaction conditions in an open-air atmosphere, and it was easy to apply on a gram scale. This novel method in detail was also explored by control experiments, providing a number of key insights. The kinetic process followed by 1H NMR indicated that the reaction was finished in 15 min. Furthermore, the mechanism of silver(I)-catalyzed hydroborylation of cyclopropenes was proposed, with the protonation by methanol as the rate-determining step.
RESUMO
Chirality widely exists in a diverse array of biologically active molecules and life forms, and the catalytic constructions of chiral molecules have triggered a heightened interest in the fields of chemistry and materials and pharmaceutical sciences. However, the synthesis of silicon-stereogenic organosilicon compounds is generally recognized as a much more difficult task than that of carbon-stereogenic centers because of no abundant organosilicon-based chiral sources in nature. Herein, we reported a highly enantioselective rhodium-catalyzed trans-selective hydrosilylation of silicon-tethered bisalkynes to access chiral benzosiloles bearing a silicon-stereogenic center. This protocol featured with chiral Ar-BINMOL-Phos bearing hydrogen-bond donors as a privileged P-ligand for catalytic asymmetric hydrosilylation that is operationally simple and has 100% atom-economy with good functional group tolerability as well as high enantioselectivity (up to >99:1 er). Benefiting from the trans-selective hydrosilylation with the aid of Rh/Ar-BINMOL-Phos-based asymmetric catalysis, the Si-stereogenic benzosiloles exhibited pronounced aggregation-induced emission (AIE) and circularly polarized luminescence (CPL) activity.
RESUMO
Hydrosilylation of unsaturated carbon-carbon bonds with hydrosilanes is a very important process to access organosilicon compounds and ranks as one of the most fundamental reactions in organic chemistry. However, catalytic asymmetric hydrosilylation of activated alkenes and internal alkenes has proven elusive, due to competing reduction of carbon-carbon double bond or isomerization processes. Herein, we report a highly enantioselective Si-C coupling by hydrosilylation of carbonyl-activated alkenes using a palladium catalyst with a chiral TADDOL-derived phosphoramidite ligand, which inhibits O-hydrosilylation/olefin reduction. The stereospecific Si-C coupling/hydrosilylation of maleimides affords a series of silyl succinimides with up to 99% yield, >99:1 diastereoselectivity and >99:1 enantioselectivity. The high degree of stereoselectivity exerts remote control of axial chirality, leading to functionalized, axially chiral succinimides which are versatile building blocks. The product utility is highlighted by the enantioselective construction of N-heterocycles bearing up to three stereocenters.
RESUMO
Sevelamer (polyallyamine resin)-supported sulfonic acid (S-SO3H) has been prepared from the reaction of sevelamer with chlorosulfonic acid and characterized using FT-IR spectroscopy, scanning electronmicroscopy (SEM) and thermogravimetric analysis (TGA). The catalytic activity of S-SO3H was investigated in the synthesis of 1,8-dioxo-octahydroxanthene derivatives. All of the reactions were fast and gave excellent yields. The catalyst was easily recovered and reused for 5 runs without significant loss of its catalytic activity.
RESUMO
The first example of palladium-catalyzed chelation-assisted C-H olefination of 2-amino biaryls using readily available vinylsilanes as unactivated olefinating reagents has been developed, affording valuable arylated vinylsilane compounds in moderate to excellent yields and with exclusive (E)-selectivities.
RESUMO
A palladium-catalyzed chelation-assisted enantioselective C-H olefination of symmetrically diaryl-substituted tetraorganosilicon derivatives was developed, enabling the generation of nitrogen-containing silicon-stereogenic tetraorganosilicon compounds with modest to good yields and good to excellent enantioselectivities (up to 95.5:4.5 e.r.). The Thorpe-Ingold effect exerted by the substituents on silicon was observed to have a profound influence on formation of olefinated products which were further converted into other relevant chiral organosilanes without the loss of enantiomeric purity, thus demonstrating the synthetic utility of the developed enantioselective olefination.
RESUMO
A palladium-catalyzed enantioselective sequential ring-opening/cross-coupling of cyclobutanones is disclosed that provides chiral indanones bearing C3-quaternary stereocenters. The reaction process involves palladium-catalyzed nucleophilic addition of cyclobutanones and aryl halides, enantioselective ß-carbon elimination, and intermolecular trapping of a transient σ-alkylpalladium complex with boronic acids. Alternatively, an intramolecular cyclopropanation is realized through C-H bond functionalization in the absence of external coupling reagents, affording chiral cyclopropane-fused-indanones in good yields and enantioselectivity.
RESUMO
A palladium-catalyzed ketoxime-chelation-assisted enantioselective C-H olefination of 2-arylcyclohex-2-enone oxime ether with a wide range of olefins as coupling partners was developed. Employing ketoxime ether as an efficient directing group, a variety of axially chiral vinyl arenes was synthesized by Pd(ii)-catalyzed C-H functionalization with excellent enantioselectivities (96 â 99% ee) under mild conditions.
RESUMO
A highly diastereo- and enantioselective silver-catalyzed azomethine ylide-imine (AYI) cycloaddition reaction of glycine aldimino esters with imines was developed in which the Xing-Phos-controlled syn-selective or DTBM-Segphos-induced anti-selective AYI cycloaddition reaction could be applied to the synthesis of a variety of stereodivergent 1-alkyl-2,5-substituted imidazolidines with high yields and excellent enantioselectivities (up to 99% ee) as well as good diastereoselectivities (up to 99:1 dr) under mild reaction conditions.
RESUMO
To shed light on the influence of reaction parameters on palladium-catalyzed tandem allylic alkylation in the presence of Fei-Phos (a chiral trans-1,2-diaminocyclohexane-derived phosphine ligand), the effect of different phosphine ligands, inorganic or organic bases, Brønsted acids, and other additives on the asymmetric palladium-catalysed alkylation of catechol with allylic diacetate was investigated. In this reaction, 2-vinyl-2,3-dihydro-benzo[1,4]dioxin products with promising enantioselectivity were achieved in good yields. In addition, a novel palladium-catalyzed three-component and one-pot allylic substitution/cyclization/reduction reaction assisted by methylphenylsilane was reported with good selectivity.
RESUMO
It was found that the tridentate O,N,O-type Schiff base ligand bearing suitable substituents was a highly effective promoter in the catalytic asymmetric bromochlorination reaction, in which the corresponding aromatic bromochloroalcohols with vicinal halogen-bearing stereocenters were formed with perfect regioselectivity, with moderate to excellent enantioselectivities (up to 93% ee), and with good yields and chemoselectivities.
RESUMO
CycloN2P2-Phos! The use of the multidentate phosphine, CycloN2P2-Phos, which contains four heteroatoms (two nitrogen and two phosphorus atoms), in the palladium-catalyzed asymmetric allylic etherification (AAE) of alcohols and silanols leads to excellent levels of enantioselectivity (up to 99 %â ee).
Assuntos
Álcoois/química , Compostos Alílicos/química , Éteres/química , Paládio/química , Fosfinas/química , Silanos/química , Catálise , Ligantes , Estrutura Molecular , EstereoisomerismoRESUMO
An interesting example of a divergent catalysis with a copper(I) and amine-functional macromolecular polysiloxanes system was successfully presented in click chemistry. In this manuscript, we demonstrate the remarkable ability of the secondary amine-functional polysiloxane to induce oxidative coupling in the copper-mediated Huisgen reactions of azides and alkynes, thereby achieving good yields and selectivities. The click reactions mediated by a polysiloxane-supported secondary amine allow the preparation of novel heterocyclic compounds, that is, bistriazoles. Comparably, it is also surprising that the use of a diamine-functional polysiloxane as ligand led to a classic Huisgen [3+2] cycloaddition in excellent yields. From the results of the present amine-functional polysiloxanes-controlled Huisgen reaction or oxidative Huisgen coupling reaction to divergent products and the proposed mechanism, we suggested that the mononuclear bistriazole-copper complex stabilized and dispersed by the secondary amine-functional polysiloxane was beneficial to prevalent the way to oxidative coupling.
Assuntos
Aminas/química , Cobre/química , Siloxanas/química , Triazóis/química , Alcinos/química , Azidas/química , Catálise , Química Click , Reação de Cicloadição , Acoplamento Oxidativo , Triazóis/síntese químicaRESUMO
A detailed experimental investigation of an aza-Michael reaction of aniline and chalcone is presented. A series of Cinchona alkaloid-derived organocatalysts with different functional groups were prepared and used in the aza-Michael and retro-aza-Michael reaction. There was an interesting finding that a complete reversal of stereoselectivity when a benzoyl group was introduced to the cinchonine and cinchonidine. The chirality amplification vs. time proceeds in the quinine-derived organocatalyst containing silicon-based bulky group, QN-TBS, -catalyzed aza-Michael reaction under solvent-free conditions. In addition, we have demonstrated for the first time that racemization was occurred in suitable solvents under mild conditions due to retro-aza-Michael reaction of the Michael adduct of aniline with chalcone. These indicate the equilibrium of retro-aza-Michael reaction and aza-Michael reaction produce the happening of chirality amplification in aza-Michael reaction and racemization via retro-aza-Michael reaction under different conditions, which would be beneficial to the development of novel chiral catalysts for the aza-Michael reactions.
Assuntos
Compostos Aza/química , Alcaloides de Cinchona/química , Catálise , EstereoisomerismoRESUMO
AIM: To establish 293T cells expressing human BTLA gene, a novel attenuator for B and T lymphocyte. METHODS: The gene encoding human BTLA was amplified by RT-PCR from PHA activated T cells, and then the target gene fragment was inserted into retrovirus vector pEGZ-Term after being digested with EcoR I and BamH I. The recombinant vector was transfected into 293T cells with LipfectAMINE 2000, and the cells was further selected with Zeocin. Effect of 293T/BTLA cells on T cells proliferation and activation in vitro was been studied by methods of MTT and cytometry. RESULTS: The stable expression of human BTLA on the transfected cell line was identified by flow cytometry analysis. In vitro, 293T/BTLA cells had an inhibitory effect on the proliferation of T cells stimulated by anti-CD3 mAb and down-regulated the expression of activation marker CD25 on the surface of T cells and decreased the secretion of IFN-gamma and IL-10. CONCLUSION: A cell line 293T/BTLA stably expressing the human BTLA protein has been obtained and it can partially inhibit the proliferation and activation of T cells in vitro.