RESUMEN
The discovery of a multiple-bond-forming process merging the singlet oxygen-mediated dearomatization of 3,4-disubstitued phenols and diastereo- and regioselective epoxidation is described. This one-pot strategy using a transition metal-free multicatalytic system comprised of rose bengal and cesium carbonate allowed the efficient formation of functionalized epoxyquinol products under mild conditions. Mechanistic investigations have been performed to shed the light on the key species involved in this transformation.
Asunto(s)
Fenoles , Elementos de Transición , Oxidación-Reducción , Rosa Bengala , Oxígeno SingleteRESUMEN
A highly enantioselective synthesis of (R,S) or (S,S)-2,6-disubstituted dehydropiperidines has been previously achieved through Sn/Li transmetalation of the corresponding stannylated dehydropiperidines or of their precursors. Herein, we successively consider their Upjohn's syn dihydroxylation and their anti-dihydroxylation via an epoxidation reaction followed by epoxide opening reaction. The stereochemical course of these reactions was first reported including the use of appropriate protecting groups before considering the conversion of the obtained compounds into NH or NMe iminosugar hydrochlorides. A primary evaluation of the designed iminosugar C-glycosides as glycosidase inhibitors suggests candidates for the selective inhibition of α-galactosidase, amyloglycosidase and naringinase. Beyond the reported results, the method constitutes a highly modulable route for the synthesis of well stereodefined iminosugar C-glycosides, an advantage which might be used for the design of iminosugars to enhance their biological properties.
Asunto(s)
Inhibidores Enzimáticos/síntesis química , Inhibidores Enzimáticos/farmacología , Glicósido Hidrolasas/antagonistas & inhibidores , Glicósidos/síntesis química , Glicósidos/farmacología , Iminoazúcares/química , Conformación de Carbohidratos , Técnicas de Química Sintética , Inhibidores Enzimáticos/química , Glicósidos/química , Modelos Moleculares , EstereoisomerismoRESUMEN
A modular autonomous flow reactor combining monitoring technologies with a feedback algorithm is presented for the synthesis of the natural product carpanone. The autonomous self-optimizing system, controlled via MATLAB, was designed as a flexible platform enabling an adaptation of the experimental setup to the specificity of the chemical transformation to be optimized. The reaction monitoring uses either online high pressure liquid chromatography (HPLC) or in-line benchtop nuclear magnetic resonance (NMR) spectroscopy. The custom-made optimization algorithm derived from the Nelder-Mead and golden section search methods performs constrained optimizations of black-box functions in a multidimensional search domain, thereby assuming no a priori knowledge of the chemical reactions. This autonomous self-optimizing system allowed fast and efficient optimizations of the chemical steps leading to carpanone. This contribution is the first example of a multistep synthesis where all discrete steps were optimized with an autonomous flow reactor.
RESUMEN
A new approach exploiting the dual properties of thiol-grafted cellulose paper for promoting copper-catalyzed [3+2]-cycloadditions of organic azides with alkynes and adsorbing residual copper species in solution was developed. The thiol-grafted cellulose paper, used as a paper strip, effects the reduction of CuII to catalytically active CuI and acts as a powerful adsorbent for copper, thereby facilitating the work-up process and leaving the crude mixture almost free of copper residues after a single filtration.
RESUMEN
This study describes extensive investigations of the Heck-Matsuda reaction carried out by continuous-flow chemistry between aryl diazonium salts generated in situ and methyl acrylate. Our optimized procedures enable sequential aniline diazotization/palladium-catalyzed Heck-Matsuda reaction using either Pd(OAc)2 or PdEnCat 30 as respectively a homogeneous or a heterogeneous source of palladium. This safe chemistry that does not require the handling of hazardous aryl diazonium salts involves inexpensive reagents and solvents, under ligand- and base-free conditions.
RESUMEN
A homemade CuONPs/Gr catalyst was found to be efficient for the C-H arylation of benzoquinone. This methodology represents the first example of a Meerwein arylation catalyzed by a heterogeneous catalyst.
RESUMEN
This review deals with the preparation of chiral, nonracemic α-aminoorganostannanes and their applications in asymmetric synthesis. The pioneering works in this field date back almost 20 years ago and since then extensive research has been carried out to develop efficient and selective routes to highly enantioenriched α-aminoorganostannanes. The facile Sn/Li transmetalation of these compounds by n-BuLi has led to various applications in stereoselective synthesis. Selected examples using chiral α-aminoorganostannanes as starting materials will be reported.
Asunto(s)
Compuestos Orgánicos de Estaño/química , Estereoisomerismo , Estaño/química , Indicadores y Reactivos , Litio/química , Metales/química , Compuestos Organometálicos/química , Compuestos Orgánicos de Estaño/síntesis químicaRESUMEN
trans-N-(Arenesulfonyl)-2-tributylstannyloxazolidines derived from (R)-phenylglycinol were diastereoselectively ring-opened by soft organometallic reagents in the presence of BF(3).OEt(2). Both higher order organocuprates and allyltributyltin afforded the desired products in good-to-excellent yields and high diastereoselectivities (dr up to 99/1). The stereochemical assignments of tributylstannyl-beta-aminoalcohols were firmly established from NMR data and after determination of several radiocrystallographic structures. Mechanisms were proposed in order to rationalize the observed selectivities.
Asunto(s)
Compuestos Orgánicos de Estaño/química , Compuestos Orgánicos de Estaño/síntesis química , Oxazoles/química , Etanolaminas , Glicina/análogos & derivados , Glicina/química , Nitrógeno/química , Propanolaminas/química , Estereoisomerismo , Especificidad por Sustrato , Valina/análogos & derivados , Valina/químicaRESUMEN
A multicatalytic photooxygenation of substituted phenols in the presence of rose bengal and cesium carbonate under green LED light is reported. This transformation enabled the introduction of both atoms of singlet oxygen and led to the one-pot synthesis of epoxyquinols in a stereoselective way.
RESUMEN
In the current study, we introduce photothiol-X chemistry as a powerful method to create hydrophobic patterns covalently grafted to the surface of cellulose paper. The general strategy builds on the use of a cellulose-based molecular printboard featuring disulfide functions which upon spatiocontrolled light irradiation at 365 nm allows robust photothiol-X ligations with hydrophobic moieties. A screening of structurally diverse molecular architectures as hydrophobic coating was conducted, and the most impressive result obtained with cholesterol moieties allows the creation of spatially well-resolved hydrophobic patterns with a contact angle of 140.8°. Our discoveries are supported by in-depth characterization studies using Fourier transform infrared spectroscopy, X-ray photoelectron spectrometry, and scanning electron microscopy analyses.
RESUMEN
A biomimetic device for the reduction of Cu(ii) to Cu(i) consisting of thioglycolic acid covalently grafted to cellulose paper was developed. The device displays exceptionally fast reducing properties allowing the reduction of Cu(ii) in seconds and the formation of deeply colored Cu(i)-SCH2R complexes onto the cellulose paper. This biomimetic and biomaterial-based concept was exploited for the detection of copper in water samples with a limit of detection as low as 2 ppm.
Asunto(s)
Materiales Biomiméticos/química , Cobre/análisis , Biomimética , Celulosa/química , Colorimetría , Cobre/química , Concentración de Iones de Hidrógeno , Límite de Detección , Microscopía Electrónica de Rastreo , Oxidación-Reducción , Papel , Espectroscopía de Fotoelectrones , Espectroscopía Infrarroja por Transformada de Fourier , Tioglicolatos/químicaRESUMEN
A portable, recyclable and highly selective paper-based sensor device for the colorimetric and optical detection of hydrogen sulfate anions in water was developed. The detection system features a rhodamine-based sensor covalently grafted onto the highly hydrophilic surface of cellulose paper.
RESUMEN
A room temperature copper-catalyzed radical arylation of pyrroles with anilines, through in situ generated aryl diazonium salts, has been developed under neutral conditions. Experimental and theoretical studies explain the crucial role of CaCO3 and the high regioselectivity observed.
RESUMEN
An original access to iminosugars from a cis/trans mixture of stannylated oxazolidinones 5 is reported. The dehydropiperidines 7-trans and 7-cis were obtained stereoselectively with an RS and SS configuration depending on the order of the Sn-Li transmetalation (followed by electrophilic trapping) and of the ring closing metathesis reactions due to the stereoselective epimerization of the α-aminoanion intermediate. The dehydropiperidines 7-trans and 7-cis were subsequently used for the synthesis of enantiopure homonojirimycin analogs.
Asunto(s)
Flavonoles/química , Iminoazúcares/síntesis química , Compuestos Orgánicos de Estaño/química , Oxazolidinonas/química , Compuestos de Vinilo/química , Iminoazúcares/química , Estructura Molecular , EstereoisomerismoRESUMEN
The electrochemical reduction of sensitive sulfonamides is described. The addition of a benzoyl group on the nitrogen atom facilitates the reductive cleavage of sulfonamides preventing ß-fragmentation and epimerization. This strategy was successfully applied to the cyclopropylamine and to α-amino stannanes.
RESUMEN
The preparation of polymer-supported allyltin reagents was shown to be possible for both unfunctionalized and functionalized allyl units. These reagents were treated with aldehydes in the presence of cerium(III) or indium(III) salts to afford high yields of homoallylic alcohols, practically uncontaminated with organotin residues (less than 5 ppm). Some mechanism aspects are briefly discussed and the potential for regeneration and reuse of these supported reagents is pointed out.
RESUMEN
[reaction: see text] Polymer-supported triorganotin halides were used in the halogenation reaction of aromatic amines. Treatment of aromatic amines with n-butyllithium and polymer-supported organotin halides gave the corresponding polymer-bound N-triorganostannylamines, which by treatment with bromine or iodine monochloride gave the para-halogenated aromatic amines with high yields and high selectivities. The polymer-supported organotin halides reagents regenerated during the course of the halogenation reaction can be reused without loss of efficiency. The presence of tin residues in halogenated aromatic amines was also investigated and evaluated at under 20 ppm after three runs.
RESUMEN
gamma-siloxyallyltributylstannanes were selectively obtained as E or Z isomers from beta-tributylstannylacrolein upon reaction with lithium or magnesium alkylcyanocuprates. The ability of the reagents to give a high syn selectivity when added to iminium salts has been used for the efficient synthesis of (+/-)-1-deoxy-6,8a-di-epi-castanospermine from succinimide. The key step of the synthesis was the allylstannation of the N-allyliminium intermediate followed by ring closing metathesis.