RESUMO
Generality in asymmetric catalysis can be manifested in dramatic and valuable ways, such as high enantioselectivity across a wide assortment of substrates in a given reaction (broad substrate scope) or as applicability of a given chiral framework across a variety of mechanistically distinct reactions (privileged catalysts). Reactions and catalysts that display such generality hold special utility, because they can be applied broadly and sometimes even predictably in new applications. Despite the great value of such systems, the factors that underlie generality are not well understood. Here, we report a detailed investigation of an asymmetric hydrogen-bond-donor catalyzed oxetane opening with TMSBr that is shown to possess unexpected mechanistic generality. Careful analysis of the role of adventitious protic impurities revealed the participation of competing pathways involving addition of either TMSBr or HBr in the enantiodetermining, ring-opening event. The optimal catalyst induces high enantioselectivity in both pathways, thereby achieving precise stereocontrol in fundamentally different mechanisms under the same conditions and with the same chiral framework. The basis for that generality is analyzed using a combination of experimental and computational methods, which indicate that proximally localized catalyst components cooperatively stabilize and precisely orient dipolar enantiodetermining transition states in both pathways. Generality across different mechanisms is rarely considered in catalyst discovery efforts, but we suggest that it may play a role in the identification of so-called privileged catalysts.
Assuntos
Éteres Cíclicos/química , Hidrocarbonetos Bromados/síntese química , Compostos de Trimetilsilil/síntese química , Catálise , Ligação de Hidrogênio , Ácidos de Lewis/química , Modelos Químicos , Estereoisomerismo , Compostos de Trimetilsilil/químicaRESUMO
In the current study, a smart approach for synthesizing trimethyl ethoxysilane-decorated magnetic-core silica-nanoparticles (TMS-mcSNPs) and its effectiveness as nanosorbents have been exploited. While the magnetite core was synthesized using the modified Mössbauer method, Stöber method was employed to coat the magnetic particles. The objective of this work is to maximize the magnetic properties and to minimize both particle size (PS) and particle size distribution (PSD). Using a full factorial design (2k-FFD), the influences of four factors on the coating process was assessed by optimizing the three responses (magnetic properties, PS, and PSD). These four factors were: (1) concentration of tetraethyl-orthosilicate (TEOS); (2) concentration of ammonia; (3) dose of magnetite (Fe3O4); and (4) addition mode. Magnetic properties were calculated as the attraction weight. Scanning electron microscopy (SEM) was used to determine PS, and standard deviation (±SD) was calculated to determine the PSD. Composite desirability function (D) was used to consolidate the multiple responses into a single performance characteristic. Pareto chart of standardized effects together with analysis of variance (ANOVA) at 95.0 confidence interval (CI) were used to determine statistically significant variable(s). Trimethyl ethoxysilane-functionalized mcSNPs were further applied as nanosorbents for magnetic solid phase extraction (TMS-MSPE) of organophosphorus and carbamate pesticides.
Assuntos
Nanopartículas Magnéticas de Óxido de Ferro/química , Praguicidas/síntese química , Silanos/síntese química , Compostos de Trimetilsilil/síntese química , Magnetismo , Nanopartículas de Magnetita/química , Nanocompostos/química , Tamanho da Partícula , Praguicidas/química , Silanos/química , Dióxido de Silício/química , Extração em Fase Sólida , Compostos de Trimetilsilil/químicaRESUMO
The total synthesis of (-)-antrocin and its enantiomer are presented. Antrocin (-)-1 is an important natural product which acts as an antiproliferative agent in a metastatic breast cancer cell line (IC50: 0.6 µM). The key features of this synthesis are: (a) selective anti-addition of trimethylsilyl cyanide (TMSCN) to α,ß-unsaturated ketone; (b) resolution of (±)-7 using chiral auxiliary L-dimethyl tartrate through formation of cyclic ketal diastereomers followed by simple column chromatography separation and acid hydrolysis; (c) substrate-controlled stereoselective aldol condensation of (+)-12 with monomeric formaldehyde and pyridinium chlorochromate (PCC) oxidation for synthesis of essential lactone core in (-)-14; and (d) non-basic Lombardo olefination of the carbonyl at the final step to yield (-)-antrocin. In addition, (+)-9 cyclic ketal diastereomer was converted to (+)-antrocin with similar reaction sequences.
Assuntos
Produtos Biológicos/síntese química , Neoplasias da Mama/tratamento farmacológico , Proliferação de Células/efeitos dos fármacos , Lactonas/síntese química , Sesquiterpenos/síntese química , Produtos Biológicos/química , Produtos Biológicos/farmacologia , Neoplasias da Mama/patologia , Linhagem Celular Tumoral , Cianetos/síntese química , Cianetos/química , Feminino , Humanos , Lactonas/química , Lactonas/farmacologia , Metástase Neoplásica , Sesquiterpenos/química , Sesquiterpenos/farmacologia , Estereoisomerismo , Tartaratos/síntese química , Tartaratos/química , Compostos de Trimetilsilil/síntese química , Compostos de Trimetilsilil/químicaRESUMO
A tantalum-catalyzed solvent-free approach for the construction of amide bonds with 1-(trimethylsilyl)imidazole is developed, and the mild reaction conditions are applicable to a wide variety of electrophilic amino acid homologues. This approach delivers a new class of peptides in high yields without any epimerization.
Assuntos
Amidas/química , Aminoácidos/química , Tantálio/química , Amidas/síntese química , Aminoácidos/síntese química , Catálise , Técnicas de Química Sintética , Imidazóis/síntese química , Imidazóis/química , Compostos de Trimetilsilil/síntese química , Compostos de Trimetilsilil/químicaRESUMO
This study developed an analytical method to determine the urushiol content in sap and several foods. The full process for urushiol analysis consists of extraction, trimethylsilyl silylation, analysis, and identification via GC-MS, with each step optimized to attain the required accuracy and precision. Urushiol was separated from sap via liquid-liquid extraction and was derivatized via silylation. The components were analyzed using a polar capillary column and identified using GC-MS. The deviations of relative retention times and retention time windows were within 0.001 and 0.02 min, which satisfied the criteria of 0.06 and 0.03 min, respectively. The response of the urushiol standards tested was found to be linear in the investigated concentration range, with a correlation coefficient of 0.998. The LODs were between 1.74 and 2.67 µg/mL.
Assuntos
Catecóis/análise , Ingredientes de Alimentos/análise , Cromatografia Gasosa-Espectrometria de Massas/métodos , Rhus/química , Catecóis/isolamento & purificação , Limite de Detecção , Extração Líquido-Líquido , Extratos Vegetais/análise , República da Coreia , Plântula/química , Compostos de Trimetilsilil/análise , Compostos de Trimetilsilil/síntese químicaRESUMO
A novel bicyclization strategy has been developed for the stereoselective synthesis of bicyclic lactones, i.e. 7-aryl or alkyl-2,6-dioxabicyclo[3.3.1]nonan-3-ones through a domino cyclization of (R)-3-hydroxyhex-5-enoic acid with an aldehyde in the presence of 10 mol% trimethylsilyltriflate under mild conditions. The salient features of this methodology are high yields, excellent selectivity, low catalyst loading and faster reaction times. This method has been successfully applied to the total synthesis of pyranopyran, tetraketide and polyrhacitide A.
Assuntos
Compostos Bicíclicos Heterocíclicos com Pontes/síntese química , Cicloexanonas/síntese química , Dissacarídeos/síntese química , Lactonas/síntese química , Piranos/síntese química , Aldeídos/síntese química , Aldeídos/química , Compostos Bicíclicos Heterocíclicos com Pontes/química , Catálise , Ciclização , Cicloexanonas/química , Dissacarídeos/química , Lactonas/química , Modelos Moleculares , Piranos/química , Estereoisomerismo , Compostos de Trimetilsilil/síntese química , Compostos de Trimetilsilil/químicaRESUMO
A class of o-(trimethylsilyl)aryl fluorosulfates was synthesized by a concise method and successfully used as aryne precursors for the first time. Different trapping agents such as azides, furans, and acyl acetoacetates could successfully react with the aryne precursors under mild conditions with good to excellent yields.
Assuntos
Acetoacetatos/química , Azidas/química , Compostos de Trimetilsilil/química , Compostos de Trimetilsilil/síntese química , Estrutura Molecular , EstereoisomerismoRESUMO
The combined use of a halogen bond (XB) donor with trimethylsilyl halide was found to be an efficient cocatalytic system for the direct dehydroxylative coupling reaction of alcohol with various nucleophiles, such as allyltrimethylsilane and trimethylcyanide, to give the corresponding adduct in moderate to excellent yields. Detailed control experiments and mechanistic studies revealed that the XB interaction was crucial for the reaction. The application of this coupling reaction is also described.
Assuntos
Álcoois/química , Halogênios/química , Compostos de Organossilício/química , Compostos de Organossilício/síntese química , Compostos de Trimetilsilil/química , Compostos de Trimetilsilil/síntese química , Ligação de Hidrogênio , Estrutura MolecularRESUMO
Acetylenic enamines generated in situ from readily available enynones and primary amines undergo thermal cyclization in diphenyl ether providing easy access to 4-aryl-2-(trimethylsilylmethylene)-1,2-dihydro-3H-pyrrol-3-ones. This reaction is inherently versatile, allowing for variations of substituents in both enynone and amine. Full regioselectivity along with short reaction time (1-2 h) and simple workup afford single products in good to excellent isolated yields. Fluorescent properties of the obtained compounds were studied.
Assuntos
Acetileno/química , Aminas/química , Pirróis/síntese química , Temperatura , Compostos de Trimetilsilil/síntese química , Ciclização , Estrutura Molecular , Pirróis/química , Estereoisomerismo , Compostos de Trimetilsilil/químicaRESUMO
The first example of a copper(I)-catalyzed intramolecular aminotrifluoromethylation of unactivated alkenes using (TMS)CF3 (trimethyl(trifluoromethyl)silane) as the CF3 source is described. A broad range of electronically and structurally varied substrates undergo convenient and step-economical transformations for the concurrent construction of a five- or six-membered ring and a C-CF3 bond toward different types of trifluoromethyl azaheterocycles. The methodology not only circumvents use of expensive electrophilic CF3 reagents or the photoredox strategy but also expands the scope to substrates that are difficult to access by the existing methods. Mechanistic studies are conducted, and a plausible mechanism is proposed.
Assuntos
Alcenos/química , Cobre/química , Compostos Heterocíclicos/química , Compostos Heterocíclicos/síntese química , Hidrocarbonetos Fluorados/química , Hidrocarbonetos Fluorados/síntese química , Compostos de Trimetilsilil/química , Compostos de Trimetilsilil/síntese química , Catálise , Estrutura Molecular , EstereoisomerismoRESUMO
The use of Me3SiO(-)/Bu4N(+) as a general activator of organotrimethylsilanes for addition reactions has been established. The broad scope of the method offers trimethylsilanes (including acetate, allyl, propargyl, benzyl, dithiane, heteroaryl, and aryl derivatives) as bench-stable organometallics that can be readily utilized as carbanion equivalents for synthesis. Reactions are achieved at rt without the requirement of specialized precautions that are commonplace for other organometallics.
Assuntos
Cátions/química , Compostos Organometálicos/química , Compostos Organometálicos/síntese química , Compostos de Organossilício/síntese química , Compostos de Amônio Quaternário/química , Compostos de Amônio Quaternário/síntese química , Quinolizinas/química , Compostos de Enxofre/química , Compostos de Trimetilsilil/química , Compostos de Trimetilsilil/síntese química , Catálise , Estrutura Molecular , Compostos de Organossilício/químicaRESUMO
Conventional allenes have not been effective π-reactive 2-carbon components in many intermolecular cycloadditions including metal-catalyzed [5 + 2] cycloadditions. We report herein that rhodium-catalyzed [5 + 2] cycloadditions of propargyltrimethylsilanes and vinylcyclopropanes provide, after in situ protodesilylation, a highly efficient route to formal allene cycloadducts. Propargyltrimethylsilanes function as safe, easily handled synthetic equivalents of gaseous allenes and hard-to-access monosubstituted allenes. In this one-flask procedure, they provide cycloadducts of what is formally addition to the more sterically encumbered allene double bond.
Assuntos
Alcadienos/química , Ródio/química , Elementos de Transição/química , Compostos de Trimetilsilil/química , Compostos de Trimetilsilil/síntese química , Catálise , Reação de Cicloadição , Estrutura Molecular , EstereoisomerismoRESUMO
The development of (trimethylsilyl)ethyl ester protected enolates is reported. The application of this class of compounds in palladium-catalyzed asymmetric allylic alkylation is explored, yielding a variety of α-quaternary six- and seven-membered ketones and lactams. Independent coupling partner synthesis engenders enhanced allyl substrate scope relative to traditional ß-ketoester substrates; highly functionalized α-quaternary ketones generated by the union of (trimethylsilyl)ethyl ß-ketoesters and sensitive allylic alkylation coupling partners serve to demonstrate the utility of this method for complex fragment coupling.
Assuntos
Compostos Alílicos/química , Paládio/química , Compostos de Trimetilsilil/química , Compostos de Trimetilsilil/síntese química , Alquilação , Ésteres , Estrutura Molecular , EstereoisomerismoRESUMO
Asymmetric cyanation of trimethylsilyl cyanide (TMSCN) with α,ß-unsaturated amides and ketones, respectively, catalyzed by bifunctional mononuclear 1,1'-bi-2-naphthol (BINOL)-Mg and binuclear bis(prophenol)-Mg catalysts was realized. A series of synthetically important 1,4-cyano products were obtained with good to high enantioselectivities (up to 97 %â ee).
Assuntos
Amidas/síntese química , Complexos de Coordenação/química , Cianetos/química , Cetonas/síntese química , Magnésio/química , Compostos de Trimetilsilil/química , Alcenos/síntese química , Alcenos/química , Amidas/química , Catálise , Cianetos/síntese química , Cetonas/química , Naftóis/química , Compostos de Trimetilsilil/síntese químicaRESUMO
A highly efficient one-pot procedure for the preparation of 1-chloroalkynes and 1-chlorobutadiynes from terminal and trialkylsilyl-protected precursors is reported. This convenient reaction, proceeding under mild conditions, utilizes N-chlorosuccinimide as the chlorinating agent and tolerates a range of functional groups.
Assuntos
Alcinos/síntese química , Cloro/química , Succinimidas/síntese química , Compostos de Trimetilsilil/síntese química , Alcinos/química , Halogenação , Estrutura Molecular , Succinimidas/química , Compostos de Trimetilsilil/químicaRESUMO
Pharmaceutical antibiotics are not easily removed from water by conventional water-treatment technologies and have been recognized as new emerging pollutants. Herein, we report the synthesis of clickable azido periodic mesoporous organosilicas (PMOs) and their use as adsorbents for the adsorption of antibiotics. Ethane-bridged PMOs, functionalized with azido groups at different densities, were synthesized by the co-condensation of 1,2-bis(trimethoxysilyl)ethane (BTME) and 3-azidopropyltrimethoxysilane (AzPTMS), in the presence of nonionic-surfactant triblock-copolymer P123, in an acidic medium. Four different alkynes were conjugated to azide-terminated PMOs by means of an efficient click reaction. The clicked PMOs showed improved adsorption capacity (241â µg g(-1)) for antibiotics (ciprofloxacin hydrochloride) compared with azido-functionalized PMOs because of the enhanced π-π stacking interactions. These results indicate that click reactions can introduce multifunctional groups onto PMOs, thus demonstrating the great potential of PMOs for environmental applications.
Assuntos
Antibacterianos/isolamento & purificação , Compostos de Organossilício/química , Adsorção , Azidas/síntese química , Azidas/química , Química Click , Etano/análogos & derivados , Etano/síntese química , Etano/química , Compostos de Organossilício/síntese química , Porosidade , Compostos de Trimetilsilil/síntese química , Compostos de Trimetilsilil/químicaRESUMO
A new and efficient synthesis of (L)-(trimethylsilyl)alanine (TMSAla) with suitable protection for use in Solid Phase Peptide Synthesis (SPPS) has been accomplished starting from glycine tert-butyl ester and using hydroxypinanone as chiral inductor. The silylated side chain was introduced by alkylation of the Schiff base intermediate with iodomethyl(trimethylsilane) at -78 °C. Among the different synthetic routes that were tested including several chiral inductors and different Schiff bases, this strategy was selected and afforded (L)-TMSAla in good chemical overall yield with 98 % ee.
Assuntos
Alanina/análogos & derivados , Compostos de Trimetilsilil/síntese química , Alanina/síntese química , Alquilação , Catálise , Glicina/análogos & derivados , Glicina/química , Estrutura Molecular , Bases de Schiff/química , EstereoisomerismoAssuntos
Aldeídos/química , Diazometano/análogos & derivados , Hidrocarbonetos Cíclicos/química , Glucosídeos Iridoides/síntese química , Ácidos de Lewis/química , Compostos de Trimetilsilil/síntese química , Catálise , Diazometano/síntese química , Diazometano/química , Glucosídeos Iridoides/química , Estrutura Molecular , Estereoisomerismo , Compostos de Trimetilsilil/químicaRESUMO
Starting from (Z)-1-trimethylsilyl-3-bromopenta-2,4-diene, a lithium-bromine exchange reaction followed by addition onto carbonyl compounds provided the corresponding dienyl alcohols. A Peterson-type γ-elimination promoted by a catalytic amount of trimethylsilyl triflate cross-conjugated gave triene systems ([3]dendralene) which rapidly reacted with the appropriate dienophiles to yield tandem intermolecular Diels-Alder cycloadducts.
Assuntos
Compostos Policíclicos/síntese química , Compostos de Trimetilsilil/química , Compostos de Trimetilsilil/síntese química , Catálise , Compostos de Trimetilsilil/metabolismoRESUMO
A general strategy for photochemical alkynylation of unreactive C(sp(3))-H bonds has been developed. After C-H abstraction by the photo-excited benzophenone, a two-carbon unit was efficiently transferred to the generated radical from 1-tosyl-2-(trimethylsilyl)acetylene to afford the alkynylated product. The present reaction enables construction of various tri- and tetra-substituted carbons from heteroatom-substituted methylenes, methines and alkanes in a highly chemoselective fashion, and would serve as a new synthetic strategy for rapid construction of complex structures.