Enantioenriched fluorinated heterocycles can be prepared through fluorocyclizations of prochiral indoles (see scheme; Ts=tosyl, Bn=benzyl, Boc=tert-butoxycarbonyl). More than twenty examples for this cascade fluorination–cyclization, which is catalyzed by cinchona alkaloids and employs N-fluorobenzenesulfonimide as the electrophilic fluorine source have been explored, an unprecedented catalytic asymmetric difluorocyclization has also identified. Detailed facts importance to specialist...

Minimal hazard: A deuterium-labeling study reveals that, contrary to prior assumption, the safe, reliable, and widely adopted method for methyl esterification of carboxylic acids using trimethylsilyldiazomethane (TMSCHN2) proceeds through concurrent acid-catalyzed methanolytic liberation diazomethane (see scheme).

Enantiomerenangereicherte fluorierte Heterocyclen können durch Fluorcyclisierungen prochiraler Indole hergestellt werden (siehe Schema; Ts=Tosyl, Bn= Benzyl, Boc=tert-Butoxycarbonyl). Mehr als 20 Beispiele dieser Fluorierungs-Cyclisierungs-Kaskade, welche von Cinchona-Alkaloiden katalysiert wird und N-Fluorbenzolsulfonimid elektrophile Fluor-Quelle nutzt, wurden untersucht. Eine katalytische asymmetrische Difluorcyclisierung war ebenfalls möglich.

A novel reactivity in gold catalysis, namely the unusual preference for 4-exo-dig cyclization allene chemistry as well rare β-hydride elimination reaction, was uncovered starting from readily available allenols.

In a single step highly functionalized buta-1,3-dienyl-substituted 2,5-dihydrofuran unit can be formed from two different α-allenol derivatives through novel heterocyclization/cross-coupling sequence (see scheme). The reactions are fast and totally chemo- regioselective: No homocoupling products or heterocycles other than the five-membered oxacycle formed. Supporting information for this article is available on WWW under http://www.wiley-vch.de/contents/jc_2002/2006/z601055_s.pdf author....

Abstract The allene moiety represents an excellent building block for cross‐coupling cyclization reactions, affording heterocyclic skeletons in a single step. This strategy is of particular interest when two different derivatives are involved series metal‐catalyzed heterocyclization processes. Concept article focused on the Pd‐catalyzed union allenic moieties, with at least one them by intramolecular cyclometalation. These new, versatile, and highly effective transformations complex...

We report the direct and selective synthesis of oxadendralenes starting from readily available bis(α‐hydroxyallenes). The designed sequence involves a hitherto unknown oxy‐Cope rearrangement allenols by supplying site for migration 1,2‐diene moiety. Moreover, so‐prepared were converted into valuable polyfunctionalized scaffolds through effective late‐stage diversification.

We describe versatile regiocontrolled metal-catalyzed heterocyclization reactions of gamma-allenol derivatives leading to a variety fused enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines. Regioselectivity control in the O-C functionalization gamma-allenols can be achieved through choice catalyst: use AuCl(3) exclusively affords La[N(SiMe(3))(2)](3) usually favors formation whereas PdCl(2) solely gives In addition, it has been observed that for Au-catalyzed...

Versatile routes that lead to a variety of functionalized enantiopure tetrahydrofurans, dihydropyrans, and tetrahydrooxepines are based on chemo-, regio-, stereocontrolled metal-catalyzed oxycyclization reactions β,γ- γ,δ-allendiols, which were readily prepared from (R)-2,3-O-isopropylideneglyceraldehyde. The application Pd(II), Pt(II), Au(III), or La(III) salts as the catalysts gives controlled access differently sized oxacycles in form. Usually, chemoselective cyclization occurred...

Monodisperse hollow magnetite microspheres were successfully synthesized by an one-step process through a tem-plate-free hydrothermal approach employing simultaneously mixture of FeCl3.6H2O and ferrocene as precursor propylene glycol-isopropanol solvent. The morphologies properties the characterized X-ray diffraction (XRD), Raman infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), photoelectron spectroscopy (XPS), adsorption nitrogen (BET method) SQUID magnetometry....

Abstract Novel, simple, and convenient strategies to diversely functionalized spirocyclic β‐lactams have been developed by using different metal‐mediated carbonyl addition/cyclization reaction sequences. Spirocyclization precursors, 2‐azetidinone‐tethered homoallylic alcohols, bromohomoallylic homopropargylic (buta‐1,3‐dien‐2‐yl)methanols, α‐allenols obtained regioselective addition of stabilized organometallic reagents azetidine‐2,3‐diones in an aqueous environment. Ruthenium‐, silver‐,...

First insights into the reaction between a Baylis-Hillman adduct and an allene moiety have been obtained from novel domino heterocyclization/cross-coupling of alpha-allenols acetates, which furnishes [(2,5-dihydrofuran-3-yl)methyl]acrylate derivatives in moderate to good yields.

Chemodivergent metal-catalyzed oxycyclization of enallenols, such as those depicted, may occur by judicious choice the catalyst, namely iron trichloride versus precious metal salts, owing to their potential ability discriminate both reactive sites.

Abstract In this contribution, we describe the role of steric interactions in Pd II ‐catalyzed reactions terminal α‐allenones, which has not previously been invoked discussions these versatile compounds. By adopting [PdCl 2 (MeCN) ] as catalyst, cycloisomerization/dimerization ratio α‐allenones is controlled by substitution allene compound: unsubstituted allenones mainly afford dimerization, whereas bearing an internal substituent favor formation cycloisomerization products. Thus, for first...

Regiocontrolled metal-catalyzed preparations of enantiopure dihydropyrans and tetrahydrooxepines have been synthesized starting from beta- gamma-allenols derived D-glyceraldehyde. The Pd(II)-catalyzed cyclizative coupling reactions beta-allenols 1 a b with allyl bromide effectively afforded tetrafunctionalized through 6-endo oxycyclization protocol, whereas the gold-, platinum-, palladium-mediated heterocyclization gamma-allenol 2 furnished 13-16 regioselective 7-endo-trig reactions....

The divergent gold-catalysed reactivity (Csp2–H versus Csp3–H) of aryloxy-tethered allenes has been uncovered.

Hollow magnetite microspheres have been synthesized by a simple process through template-free hydrothermal approach. were surface modified coating with silica nanolayer. Pristine and hollow microparticles characterized field-emission electron microscopy, transmission X-ray diffraction, photoelectron spectroscopy, FT-IR Raman VSM magnetometry. The potential application of the as drug carrier was evaluated using Rhodamine B methotrexate model drugs. loading release kinetics both molecules...

A modified route to synthesize graphene flakes is proposed using the Chemical Vapor Deposition (CVD) technique, by copper substrates as supports. The carbon source used was ethanol, synthesis temperature 950°C and pressure controlled along whole process. In this CVD process incorporation of produced at low inducing appearance a plasma blue flash inside quartz tube. Apparently, presence required for obtaining flakes. synthesized characterized different techniques, showing non-oxidized with...

The gold-, palladium- and lanthanum-catalyzed oxycyclization reactions of azetidin-2-one-tethered gamma-allenol derivatives to a variety fused enantiopure tetrahydrofurans, dihydropyrans, tetrahydrooxepines have been developed experimentally (Part 1, accompanying paper). mechanisms these regiocontrolled metal-catalyzed heterocyclization now computationally explored at the DFT level 2). energies reaction intermediates transition states for different possible pathways calculated in various...

Eine einzige Stufe führt zu hoch funktionalisierten Buta-1,3-dienyl-substituierten 2,5-Dihydrofuranen. Die neuartige Heterocyclisierungs-Kreuzkupplungs-Sequenz (siehe Schema) verläuft ausgehend von zwei verschiedenen α-Allenol-Derivaten schnell sowie vollständig chemo- und regioselektiv: Es entstehen keine Homokupplungsprodukte oder andere Heterocyclen als der fünfgliedrige Oxacyclus.

Umkehrschluss möglich: Der 5-exo-trig-Cyclisierungsweg von γ-Allenolen lässt sich vollständig umkehren, indem ein anderes Metall gewählt (Pd statt Au) oder eine (Methoxymethyl)oxy-Schutzgruppe verwendet wird. Als Ergebnis dominiert dann die 7-endo-trig-Alkoxycyclisierung (siehe Schema; MOM=MeOCH2, Z1=tBuMe2Si, ArCO). Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2001/2007/z701611_s.pdf or from author. Please note: The publisher not...

Abstract Positive discrimination : Chemo‐ and regioselective palladium‐catalyzed cycloetherification of allendiols, namely β,γ‐ γ,δ‐allendiols, may occur by judicious choice conditions owing to their potential ability discriminate between both nucleophilic sites (see scheme). magnified image

Abstract An efficient chemodivergent metal‐controlled methodology for the generation of different highly functionalized oxygen heterocycles from common enallenol substrates has been developed. Chemoselectivity control in OC functionalization an can be achieved through choice catalyst: AuCl 3 , PdCl 2 and [PtCl (CH CH )] exclusively afford dihydrofurans selective activation allenol moiety, whereas FeCl solely gives tetrahydrofurans or tetrahydropyrans alkenol moiety. We have also shown that...

The synthesis of 2-allenyl-2-substituted-3,3-difluoroindolines has been accomplished, taking advantage the reaction between <italic>N</italic>-allenyl-indoles and Selectfluor under iron catalysis.