Showing papers on "Alkene published in 2018"
27 Apr 2018
TL;DR: Transition-metal-catalysed hydrosilylation and hydroboration reactions are valuable in the synthesis of commodity and fine chemicals, respectively and the catalyst design principles that enable us to perform these reactions using catalysts based on earth-abundant metals are described.
Abstract: The addition of a silicon-hydrogen or a boron-hydrogen bond across a carbon-carbon multiple bonds is a well-established method for the introduction of versatile silane and borane functional groups to base hydrocarbon feedstocks. Transition metal catalysis, historically with precious second- and third- row transition metals, has been used to broaden the scope of the hydrofunctionalization reaction, improve reaction rate and enhance selectivity. The anti-Markovnikov selectivity of platinum-catalyzed hydrosilylation of alkenes, for example, is an enabling synthetic technology in the multibillion-dollar silicones industry. Increased emphasis on sustainable catalytic methods and more economic processes has shifted focus to catalysis with more earth-abundant transition metals such as iron, cobalt and nickel. This review describes contemporary approaches and offers a contextual analysis of catalytic alkene hydrosilylation and hydroboration reactions using first-row transition metals. Emphasis is placed on defining advances in the field, what constitutes catalyst cost, safety, and important design features to enable precious metal-like reactivity, as well as new chemistry that is unique to first-row transition metals.
716 citations
TL;DR: An enantioselective cyanations and arylations of benzylic radicals have been demonstrated in the presence of chiral Box/Cu(I) catalysts, and a series of asymmetric difunctionalizations of styrenes have been successfully achieved.
Abstract: ConspectusThe direct transformation of C–H bonds into diverse functional groups represents one of the most atom- and step-economical strategies for organic synthesis and has received substantial attention over the last few decades. Despite recent advances, asymmetric C–H bond functionalizations are less developed, especially asymmetric oxidations of sp3 C–H bonds. Inspired by enzyme (e.g., P450) catalysis, chemists have made great efforts to develop non-enzymatic systems for enantioselective oxidations of sp3 C–H bonds. However, the involvement of highly reactive radical intermediates makes enantioselective transformations extremely challenging.In this Account, we present our recent studies on the enantioselective induction of prochiral benzylic radicals using a chiral bisoxazoline (Box)/Cu catalytic system. This reaction system was developed on the basis of our extensive studies of copper-catalyzed intermolecular alkene difunctionalizations, such as azidotrifluoromethylations, trifluoromethylcyanations, ...
494 citations
TL;DR: In this paper, a review of recent progress in the field of homogeneously catalyzed reactions using pincer-type complexes of cobalt and manganese is presented, including acceptorless dehydrogenation, hydrogenation, dehydrogenative coupling, hydrogen borrowing, hydrogen transfer, H-X additions, C-C coupling, alkene polymerization and N2 fixation.
Abstract: Homogeneous catalysis of organic transformations by metal complexes has been mostly based on complexes of noble metals. In recent years, tremendous progress has been made in the field of base-metal catalysis, mostly with pincer-type complexes, such as iron, cobalt, nickel, and manganese pincer systems. Particularly impressive is the explosive growth in the catalysis by Mn-based pincer complexes, the first such complexes being reported as recently as 2016. This review covers recent progress in the field of homogeneously catalyzed reactions using pincer-type complexes of cobalt and manganese. Various reactions are described, including acceptorless dehydrogenation, hydrogenation, dehydrogenative coupling, hydrogen borrowing, hydrogen transfer, H–X additions, C–C coupling, alkene polymerization and N2 fixation, including their scope and brief mechanistic comments.
480 citations
TL;DR: A visible-light-promoted metal-free difunctionalization of alkenes using abundant CO2 and readily available Si-H and C(sp3 )-H bonds as feedstocks is developed.
Abstract: Catalytic alkene difunctionalization via Si-H and C-H activations represents an ideal atom- and step-economic pathway for quick assembly of molecular complexity. We herein developed a visible-light-promoted metal-free difunctionalization of alkenes using abundant CO2 and readily available Si-H and C(sp3 )-H bonds as feedstocks. Through the merger of photoredox and hydrogen-atom-transfer catalysis, a variety of value-added compounds, such as β-silacarboxylic acids and acids bearing a γ-heteroatom (e.g., N, O, S) could be directly accessed from simple alkenes in a redox-neutral fashion.
261 citations
TL;DR: A catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivities to provide 2,2-diarylethylamines is reported, well suited for use in a variety of synthetic endeavors.
Abstract: Alkene aminoarylation with a single, bifunctional reagent is a concise synthetic strategy. We report a catalytic protocol for the addition of arylsulfonylacetamides across electron-rich alkenes with complete anti-Markovnikov regioselectivity and excellent diastereoselectivity to provide 2,2-diarylethylamines. In this process, single-electron alkene oxidation enables carbon-nitrogen bond formation to provide a key benzylic radical poised for a Smiles-Truce 1,5-aryl shift. This reaction is redox-neutral, exhibits broad functional group compatibility, and occurs at room temperature with loss of sulfur dioxide. As this process is driven by visible light, uses readily available starting materials, and demonstrates convergent synthesis, it is well suited for use in a variety of synthetic endeavors.
250 citations
TL;DR: The fabrication of single-atom Pt1δ+/TiO2 catalyst accomplishes a reasonable use of Pt through recycling and maximum atom-utilized efficiency, indicating the potential to achieve a green hydrosilylation industry.
Abstract: The hydrosilylation reaction is one of the largest-scale application of homogeneous catalysis and is widely used to enable the commercial manufacture of silicon products. However, considerable issues including disposable platinum consumption, undesired side reactions and unacceptable catalyst residues still remain. Here, we synthesize a heterogeneous partially charged single-atom platinum supported on anatase TiO2 (Pt1δ+/TiO2) catalyst via an electrostatic-induction ion exchange and two-dimensional confinement strategy, which can catalyze hydrosilylation reaction with almost complete conversion and produce exclusive adduct. Density functional theory calculations reveal that unexpected property of Pt1δ+/TiO2 originates from atomic dispersion of active species and unique partially positive charge Ptδ+ electronic structure that conventional nanocatalysts do not possess. The fabrication of single-atom Pt1δ+/TiO2 catalyst accomplishes a reasonable use of Pt through recycling and maximum atom-utilized efficienc...
236 citations
TL;DR: A three-component nickel-catalyzed carboacylation of olefins which enables the rapid construction of ketones with high levels of complexity and diversity and allows for facile access to a wide range of important β-fluoroalkyl ketones from simple starting materials.
Abstract: The development of catalytic carboacylation of simple olefins, which would enable the rapid construction of ketones with high levels of complexity and diversity, is very challenging. To date, the vast majority of alkene carboacylation reactions are typically restricted to single- and two-component methodologies. Here we describe a three-component carboacylation of alkenes via the merger of radical chemistry with nickel catalysis. This reaction manifold utilizes a radical relay strategy involving radical addition to an alkene followed by alkyl radical capture by an acyl-nickel complex to forge two vicinal C−C bonds under mild conditions. Excellent chemoselectivity and regioselectivity have been achieved by utilizing a pendant weakly chelating group. This versatile protocol allows for facile access to a wide range of important β-fluoroalkyl ketones from simple starting materials. To date the carboacylation of alkenes has been reported only in single- and two-component methodologies. Here, the authors report a three-component nickel-catalyzed carboacylation of olefins which enables the rapid construction of ketones with high levels of complexity and diversity.
195 citations
TL;DR: The reactions comprise a regioselective perfluoroalkyl radical addition with subsequent alkenyl migration and concomitant deprotonation to generate a ketyl radical anion that sustains the chain as a single‐electron‐transfer reducing reagent.
Abstract: Transition-metal-free radical α-perfluoroalkylation with the accompanying vicinal β-alkenylation of unactivated alkenes is presented. These radical cascades proceed by means of 1,4- or 1,5-alkenyl migration by electron catalysis on readily accessed allylic alcohols. The reactions comprise a regioselective perfluoroalkyl radical addition with subsequent alkenyl migration and concomitant deprotonation to generate a ketyl radical anion that sustains the chain as a single-electron-transfer reducing reagent.
192 citations
TL;DR: A mechanistic model of the reaction is advanced through the use of reaction progress kinetic analysis (RPKA), radical clock experiments, and stoichiometric studies, concluding that the reaction proceeds through an unprecedented alkylcobalt to nickel direct transmetalation.
Abstract: Cobalt/nickel-dual catalyzed hydroarylation of terminal olefins with iodoarenes builds complexity from readily available starting materials, with a high preference for the Markovnikov (branched) product Here, we advance a mechanistic model of this reaction through the use of reaction progress kinetic analysis (RPKA), radical clock experiments, and stoichiometric studies Through exclusion of competing hypotheses, we conclude that the reaction proceeds through an unprecedented alkylcobalt to nickel direct transmetalation Demonstration of catalytic alkene prefunctionalization, via spectroscopic observation of an organocobalt species, distinguishes this Csp2–Csp3 cross-coupling method from a conventional transmetalation process, which employs a stoichiometric organometallic nucleophile, and from a bimetallic oxidative addition of an organohalide across nickel, described by radical scission and subsequent alkyl radical capture at a second nickel center A refined understanding of the reaction leads to an op
191 citations
TL;DR: The present review provides a report of the state of the art in this autotandem hydroaminomethylation catalysis and should open prospects in the design of less expensive and abundant metal complexes for reaching at low cost similar and even superior performances.
Abstract: In the context of atom economy and low environmental impact, synthesis of amines by an efficient catalytic process is of great importance to produce these building blocks for fine chemical industry. The one-pot hydroaminomethylation of alkenes is a tandem reaction which involves three successive steps under CO/H2 pressure to perform the catalyzed hydroformylation of the alkene into the corresponding aldehyde followed by its condensation with a N–H function and the catalyzed hydrogenation of the imine/enamine intermediate into the corresponding saturated amine. Rhodium and more recently ruthenium complexes have been designed to combine high conversions of the reactants and chemoselectivity in the expected amines with high regioselectivity in either the linear or the branched amine. The coordination sphere of the metal according to the presence of ligands, temperature, CO/H2 partial pressures, and nature of the solvent is essential for complying with these selectivity requirements. The rate of the hydroform...
187 citations
Abstract: Transition-metal-catalyzed alkene hydrosilylation is one of the most important homogeneous catalytic reactions, and the development of methods that use base metals, especially iron, as catalysts for this transformation is a growing area of research. However, the limited number of ligand scaffolds applicable for base-metal-catalyzed alkene hydrosilylation has seriously hindered advances in this area. Herein, we report the use of 1,10-phenanthroline ligands in base-metal catalysts for alkene hydrosilylation. In particular, iron catalysts with 2,9-diaryl-1,10-phenanthroline ligands exhibit unexpected reactivity and selectivity for hydrosilylation of alkenes, including unique benzylic selectivity with internal alkenes, Markovnikov selectivity with terminal styrenes and 1,3-dienes, and excellent activity toward aliphatic terminal alkenes. According to the mechanistic studies, the unusual benzylic selectivity of this hydrosilylation initiates from π-π interaction between the phenyl of the alkene and the phenanthroline of the ligand. This ligand scaffold and its unique catalytic model will open possibilities for base-metal-catalyzed hydrosilylation reactions.
TL;DR: A highly Markovnikov-selective, dual-catalytic olefin hydroarylation that tolerates arenes and heteroarenes of any electronic character is reported.
Abstract: Alkene hydroarylation forms carbon–carbon bonds between two foundational building blocks of organic chemistry: olefins and aromatic rings. In the absence of electronic bias or directing groups, only the Friedel–Crafts reaction allows arenes to engage alkenes with Markovnikov selectivity to generate quaternary carbons. However, the intermediacy of carbocations precludes the use of electron-deficient arenes, including Lewis basic heterocycles. Here we report a highly Markovnikov-selective, dual-catalytic olefin hydroarylation that tolerates arenes and heteroarenes of any electronic character. Hydrogen atom transfer controls the formation of branched products and arene halogenation specifies attachment points on the aromatic ring. Mono-, di-, tri-, and tetra-substituted alkenes yield Markovnikov products including quaternary carbons within nonstrained rings.
TL;DR: Mechanistic experiments and computations suggest a mechanism in which the Lewis base activated B2 cat2 unit intercepts an alkyl radical generated by single-electron transfer (SET) from a boron-based reductant.
Abstract: An efficient method for the metal-free deaminative borylation of alkylamines, using bis(catecholato)diboron as the boron source, to directly synthesize various alkyl potassium trifluoroborate salts is introduced. The key to this high reactivity is the utilization of pyridinium salt activated alkylamines, with a catalytic amount of a bipyridine-type Lewis base as a promoter. This transformation shows good functional-group compatibility (e.g., it is unimpeded by the presence of a ketone, indole, internal alkene, or unactivated alkyl chloride) and can serve as a powerful synthetic tool for borylation of amine groups in complex compounds. Mechanistic experiments and computations suggest a mechanism in which the Lewis base activated B2 cat2 unit intercepts an alkyl radical generated by single-electron transfer (SET) from a boron-based reductant.
TL;DR: In this article, a relay relay hydroarylamination of distal and proximal olefins, and of olefin isomeric mixtures, has been achieved through NiH-catalyzed alkene isomerization and sequential reductive hydroarylation with nitroarenes.
TL;DR: A new NCP-type pincer iridium complex (BQ-NCOP)IrHCl containing a rigid benzoquinoline backbone has been developed for efficient, mild TH of unactivated C-C multiple bonds with ethanol, forming ethyl acetate as the sole byproduct.
Abstract: The first general catalytic approach to effecting transfer hydrogenation (TH) of unactivated alkenes using ethanol as the hydrogen source is described. A new NCP-type pincer iridium complex (BQ-NCOP)IrHCl containing a rigid benzoquinoline backbone has been developed for efficient, mild TH of unactivated C–C multiple bonds with ethanol, forming ethyl acetate as the sole byproduct. A wide variety of alkenes, including multisubstituted alkyl alkenes, aryl alkenes, and heteroatom-substituted alkenes, as well as O- or N-containing heteroarenes and internal alkynes, are suitable substrates. Importantly, the (BQ-NCOP)Ir/EtOH system exhibits high chemoselectivity for alkene hydrogenation in the presence of reactive functional groups, such as ketones and carboxylic acids. Furthermore, the reaction with C2D5OD provides a convenient route to deuterium-labeled compounds. Detailed kinetic and mechanistic studies have revealed that monosubstituted alkenes (e.g., 1-octene, styrene) and multisubstituted alkenes (e.g., cy...
TL;DR: In this paper, an electrochemical oxidative alkoxysulfonylation of alkenes using sulfonyl hydrazines with alcohols is accomplished, which leads to the easy accessibility of β-alkoxy sulfones, which are not only valuable architectures of many biologically active molecules, but also key building blocks for various organic transformations.
Abstract: An electrochemical oxidative alkoxysulfonylation of alkenes using sulfonyl hydrazines with alcohols is accomplished, which leads to the easy accessibility of β-alkoxy sulfones, which are not only valuable architectures of many biologically active molecules, but also key building blocks for various organic transformations. Notably, for this efficient electrochemical synthesis protocol, neither metal catalysts nor exogenous additives/oxidants are required. In addition, molecular nitrogen and hydrogen were the sole byproducts in the reaction.
TL;DR: A novel Pd/g-C3 N4 stabilized Pickering emulsion microreactor is developed, in which alkenes are hydrogenated in the oil phase with hydrogen originating from AB in the water phase, catalysed by the Pd nanoparticles at the interfaces, for more economical hydrogen utilization over conventional systems.
Abstract: Direct hydrogenation of C=C double bonds is a basic transformation in organic chemistry which is vanishing from simple practice because of the need for pressurized hydrogen. Ammonia borane (AB) has emerged as a hydrogen source through its safety and high hydrogen content. However, in conventional systems the hydrogen liberated from the high‐cost AB cannot be fully utilized. Herein, we develop a novel Pd/g‐C3N4 stabilized Pickering emulsion microreactor, in which alkenes are hydrogenated in the oil phase with hydrogen originating from AB in the water phase, catalysed by the Pd nanoparticles at the interfaces. This approach is advantageous for more economical hydrogen utilization over conventional systems. The emulsion microreactor can be applied to a range of alkene substrates, with the conversion rates achieving >95 % by a simple modification.
TL;DR: A Ni-catalyzed hydroarylation of styrenes and 1,3-dienes with organoboron compounds with new strategy that uses the proton of methanol to generate the active catalyst species Ni-H was developed.
Abstract: A Ni-catalyzed hydroarylation of styrenes and 1,3-dienes with organoboron compounds has been developed. The reaction offers a highly selective approach to diarylalkanes and allylarenes under redox-neutral conditions. In this hydroarylation reaction, a new strategy that uses the proton of methanol to generate the active catalyst species Ni-H was developed. The Ni-catalyzed hydroarylation, combined with a Ir-catalyzed C-H borylation, affords a very efficient and straightforward access to a retinoic acid receptor agonist.
TL;DR: This reaction is nicely complementary to enantioselective trifluoromethylthiolation, allylic functionalization, and intermolecular alkene difunctionalization.
Abstract: New approaches for the synthesis of enantiopure trifluoromethylthiolated molecules by chiral selenide-catalyzed allylic trifluoromethylthiolation and intermolecular difunctionalization of unactivated alkenes are disclosed. In these transformations, functional groups were well tolerated, and the desired products were obtained in good yields with excellent chemo-, enantio-, and diastereoselectivities. This reaction is nicely complementary to enantioselective trifluoromethylthiolation, allylic functionalization, and intermolecular alkene difunctionalization.
TL;DR: A photoredox‐catalyzed decarboxylative radical addition–polar cyclization cascade approach to functionalized cyclopropanes is described, demonstrating exquisite functional group tolerance.
Abstract: Herein, we describe the development of a photoredox-catalyzed decarboxylative radical addition-polar cyclization cascade approach to functionalized cyclopropanes. Reductive termination of radical-polar crossover reactions between aliphatic carboxylic acids and electron-deficient alkenes yielded carbanion intermediates that were intercepted in intramolecular alkylations with alkyl chlorides appended to the alkene substrate. The mild conditions, which make use of a readily available organic photocatalyst and visible light, were demonstrated to be amenable to a broad range of structurally complex carboxylic acids and a wide variety of chloroalkyl alkenes, demonstrating exquisite functional group tolerance.
TL;DR: This methodology, which is operationally simple using low catalyst loading without additional activator, shows excellent enantioselectivity and can be used to convert various internal alkenes with regio- and stereoisomers to valuable chiral secondary organoboronates with good functional group tolerance.
Abstract: Recent years have witnessed the growing interest in the remote functionalization of alkenes for it offers a strategy to activate the challenging C-H bonds distant from the initiation point via alkene isomerization/functionalization. However, the catalytic enantioselective isomerization/functionalization with one single transition metal catalyst remains rare. Here we report a highly regio- and enantioselective cobalt-catalyzed remote C-H bond borylation of internal alkenes via sequential alkene isomerization/hydroboration. A chiral ligand featured twisted pincer, anionic, and non-rigid characters is designed and used for this transformation. This methodology, which is operationally simple using low catalyst loading without additional activator, shows excellent enantioselectivity and can be used to convert various internal alkenes with regio- and stereoisomers to valuable chiral secondary organoboronates with good functional group tolerance.
TL;DR: Catalyst-controlled diastereoselectivity in the fluorination of chiral allylic amines enabled the preparation of highly enantioenriched 1,3-difluoro-2-amines bearing three contiguous stereocenters, and the enantioselective catalytic method was applied successfully to other classes of multifunctional alkene substrates to afford anti-β-fluoropyrrolidines.
Abstract: The stereoselective synthesis of syn-β-fluoroaziridine building blocks via chiral aryl iodide-catalyzed fluorination of allylic amines is reported. The method employs HF-pyridine as a nucleophilic fluoride source together with mCPBA as a stoichiometric oxidant, and affords access to arylethylamine derivatives featuring fluorine-containing stereocenters in high diastereo- and enantioselectivity. Catalyst-controlled diastereoselectivity in the fluorination of chiral allylic amines enabled the preparation of highly enantioenriched 1,3-difluoro-2-amines bearing three contiguous stereocenters. The enantioselective catalytic method was applied successfully to other classes of multifunctional alkene substrates to afford anti-β-fluoropyrrolidines, as well as a variety of 1,2-oxyfluorinated products.
TL;DR: The use of electrochemistry to promote these oxidative alkene 1,2-difunctionalization reactions not only obviates the need for transition-metal catalysts and oxidizing reagents but also ensures high regio- and chemoselectivity to afford homopropargylic or homoallylic alcohols.
Abstract: Unprecedented hydroxy-alkynylation and -alkenylation reactions of arylalkenes have been developed through electrochemically enabled addition of an organotrifluoroborate reagent and H2O across the double bond of the alkene. The use of electrochemistry to promote these oxidative alkene 1,2-difunctionalization reactions not only obviates the need for transition-metal catalysts and oxidizing reagents but also ensures high regio- and chemoselectivity to afford homopropargylic or homoallylic alcohols. The possibility of extending the electrochemical alkene difunctionalization strategy to other alkene carbo-heterofunctionalization reactions has been demonstrated.
TL;DR: In this article, a Na2CO3 salt-assisted one-pot pyrolysis strategy with isolated Pt single atomic sites (Pt-ISA/NG) with Pt loading up to 5.3 wt % was reported.
Abstract: Development of noble-metal single atomic site catalysts with high metal loading is highly required for many important chemical reactions but proves to be very challenging. Herein, we report a Na2CO3 salt-assisted one-pot pyrolysis strategy from EDTA–Pt complex to N-doped graphene with isolated Pt single atomic sites (Pt-ISA/NG) with Pt loading up to 5.3 wt %. The X-ray absorption fine structure analysis and spherical aberration-correction electron microscopy demonstrate an atomic dispersion of single Pt species on graphene support and stabilized by nitrogen in Pt–N4 structure. The Pt-ISA/NG catalyst exhibits high catalytic activity and reusability for anti-Markovnikov hydrosilylation of various terminal alkenes with industrially relevant tertiary silanes under mild conditions. In hydrosilylation of 1-octene, the Pt-ISA/NG catalyst delivers an overall turnover frequency of 180 h–1, which is a 4-fold enhancement compared with commercial Pt/C.
TL;DR: An efficient protocol for the direct allylic C(sp3 )-H bond activation of unactivated tri- and tetrasubstituted alkenes and their functionalization with aryl- and vinylbromides by nickel and visible-light photocatalysis has been developed.
Abstract: An efficient protocol for the direct allylic C(sp3 )-H bond activation of unactivated tri- and tetrasubstituted alkenes and their functionalization with aryl- and vinylbromides by nickel and visible-light photocatalysis has been developed. The method allows C(sp2 )-C(sp3 ) formation under mild reaction conditions with good functional-group tolerance and excellent regioselectivity.
TL;DR: A palladium(II)-catalyzed alkene difunctionalization reaction has been developed, wherein B2pin2 is used to trap chelation-stabilized alkylpalladium( II) intermediates that are formed upon nucleopalladation.
Abstract: A palladium(II)-catalyzed alkene difunctionalization reaction has been developed, wherein B2pin2 is used to trap chelation-stabilized alkylpalladium(II) intermediates that are formed upon nucleopalladation A range of carbon and nitrogen nucleophiles were found to be suitable coupling partners in this transformation, providing moderate to high yields Both 3-butenoic and 4-pentenoic acid derivatives were reactive substrate classes, affording β,γ- and γ,δ-difunctionalized carboxylic acid derivatives This work represents a new strategy to synthesize highly functionalized secondary boronates that complements existing methods
TL;DR: This work presents a metal-free photoredox strategy for the formation of C(sp3)–C(sp) and C( sp3)-C( sp2) bonds from redox-activated primary amine derivatives, suitable for synthesis of (E)-alkenes from vinyl phenyl sulfones.
Abstract: The amino group represents one of the most prevalent structural motifs in organic chemistry. Therefore, application of amines as alkylating agents in synthesis is highly compelling. Herein, we pres...
TL;DR: A combined experimental and computational study now provides a comprehensive mechanistic picture of the hydrogenation of internal alkynes with [Cp*Ru]-based catalysts, which confirms direct trans-delivery of H2, the formation of carbene intermediates by gem-hydrogenation, and their evolution into product and side products alike.
Abstract: The hydrogenation of internal alkynes with [Cp*Ru]-based catalysts is distinguished by an unorthodox stereochemical course in that E-alkenes are formed by trans-delivery of the two H atoms of H2. A combined experimental and computational study now provides a comprehensive mechanistic picture: a metallacyclopropene (η2-vinyl complex) is primarily formed, which either evolves into the E-alkene via a concerted process or reacts to give a half-sandwich ruthenium carbene; in this case, one of the C atoms of the starting alkyne is converted into a methylene group. This transformation represents a formal gem-hydrogenation of a π-bond, which has hardly any precedent. The barriers for trans-hydrogenation and gem-hydrogenation are similar: whereas DFT predicts a preference for trans-hydrogenation, CCSD(T) finds gem-hydrogenation slightly more facile. The carbene, once formed, will bind a second H2 molecule and evolve to the desired E-alkene, a positional alkene isomer or the corresponding alkane; this associative p...
TL;DR: The first direct aziridination of triaryl-substituted alkenes was achieved by means of an electrochemical process that could extend to multisubstituting styrenes.
Abstract: The first direct aziridination of triaryl-substituted alkenes was achieved by means of an electrochemical process that could extend to multisubstituted styrenes. Specifically, hexafluoroisopropanol sulfamate was used as a nucleophilic nitrogen source. Mechanistic experiments suggest that this electrochemical process proceeds by stepwise formation of two C-N bonds through reactions between cationic carbon species and the sulfamate.
TL;DR: A sulfenium-ion-initiated, catalytic, enantioselective polyene cyclization is described, and the utility of this method is demonstrated by the enantiOSElective syntheses of (+)-ferruginol and (+)-hinokiol.
Abstract: A sulfenium-ion-initiated, catalytic, enantioselective polyene cyclization is described. Homogeranylarenes and ortho-geranylphenols undergo polycyclization in good yield, diastereoselectivity, and enantioselectivity. The stereodetermining step is the generation of an enantiomerically enriched thiiranium ion from a terminal alkene and a sulfenylating agent in the presence of a chiral Lewis basic catalyst. The use of hexafluoroisopropyl alcohol as the solvent is crucial to obtain good yields. The thioether moiety resulting from the reaction can be subsequently transformed into diverse oxygen and carbon functionality postcyclization. The utility of this method is demonstrated by the enantioselective syntheses of (+)-ferruginol and (+)-hinokiol.