Abstract: Complexes in which a sigma-H--E bond (E=H, B, Si, C) acts as a two-electron donor to the metal center are called sigma complexes. Clues that it is possible to interconvert sigma ligands without a change in oxidation state derive from C--H activation reactions effecting isotope exchange and from dynamic rearrangements of sigma complexes (see Frontispiece). Through these pathways, metathesis of M--E bonds can occur at late transition metals. We call this process sigma-complex-assisted metathesis, or sigma-CAM, which is distinct from the familiar sigma-bond metathesis (typical for d(0) metals and requiring no intermediate) and from oxidative-reductive elimination mechanisms (inherently requiring intermediates with changed oxidation states and sometimes involving sigma complexes). There are examples of sigma-CAM mechanisms in catalysis, especially for alkane borylation and isotope exchange of alkanes. It may also occur in silylation and alkene hydrogenation.

Abstract: PREFACE TO THE SECOND EDITION. 1. INTRODUCTION. 1.1 The Structure and Forms of Water. 1.2 Properties of Water. 1.3 Solvation. 1.4 Hydrophobic Effect. 1.5 Salt Effect. 1.6 Water Under Extreme Conditions. References. 2. ALKANES. 2.1 Oxygenation of Alkanes. 2.2 Halogenation of Alkanes. 2.3 Formation of Carbon-Carbon Bonds. 2.4 D/H Exchange of Alkanes in Water. References. 3. ALKENES. 3.1 Reduction. 3.2 Electrophilic Additions. 3.3 Radical Reactions of Alkenes. 3.4 Carbene Reactions. 3.5 Alkene Isomerization. 3.6 Transition-Metal Catalyzed C-C Formation Reactions. 3.7 Olefin Metathesis. 3.8 Reaction of Allylic C-H Bond. 4. ALKYNES. 4.1 Reaction of Terminal Alkynes. 4.2 Additions of C C bonds. 4.3 Transition-Metal Catalyzed Cycloadditions. 4.4 Other Reactions. References. 5. ALCOHOLS, PHENOLS, ETHERS, THIOLS, AND THIOETHERS. 5.1 Oxidation of Alcohols. 5.2 Substitutions/Elimination. 5.3 Addition of Alcohols, Phenols, and Thiols to Alkene and Alkyne Bonds. 5.4 Addition of Alcohols to C=O Bonds: Esterification and Acetal Formations. 5.5 Reaction of Ethers and Cyclic Ethers. 5.6 Reaction of Sulfur Compounds. 6. ORGANIC HALIDES. 6.1 General. 6.2 Reduction. 6.3 Elimination Reactions. 6.4 Nucleophilic Substitutions. 6.5 Reductive Coupling. 6.6 Carbonylation of Organic Halides. 6.7 Transition-Metal Catalyzed Coupling Reactions. References. 7. AROMATIC COMPOUNDS. 7.1 General. 7.2 Substitution Reactions. 7.3 Oxidation Reactions. 7.4 Reductions. References. 8. ALDEHDYE AND KETONES. 8.1 Reduction. 8.2 Oxidation. 8.3 Nucleophilic Addition: C-C Bond Formation. 8.4 Pinacol Coupling. 8.5 Other Reactions (Halogenation and Oxidation of alpha-H). References. 9. CARBOXYLIC ACIDS AND DERIVATIVES. 9.1 General. 9.2 Carboxylic Acids. 9.3 Carboxylic Acid Derivatives. References. 10. CONJUGATED CARBONYL COMPOUNDS. 10.1 Reduction. 10.2 Epoxidation, Dihydroxylation, Hydroxyamination. 10.3 Conjugate Addition: Heteroatom. 10.4 C-C Bond Formation. 10.5 Other Reactions. References. 11. NITROGEN COMPOUNDS. 11.1 Amines. 11.2 Imines. 11.3 Diazo Compounds. 11.4 Azides. 11.5 Nitro Compounds. References. 12. PERICYCLIC REACTIONS. 12.1 Introduction. 12.2 Diels-Alder Reactions. 12.3 Sigmatropic Rearrangements. 12.4 Photochemical Cycloaddition Reactions. References. INDEX.

Abstract: Palladium-catalyzed methods for the aerobic oxidative coupling of alkenes and oxygen nucleophiles (e.g., water and carboxylic acids) have been known for nearly 50 years. The present account summarizes our development of analogous aerobic oxidative amination reactions, including the first intermolecular aza-Wacker reactions compatible with the use of unactivated alkenes. The reactions are initiated by intra- or intermolecular aminopalladation of the alkene. The resulting alkylpalladium(II) intermediate generally undergoes β-hydride elimination to produce enamides or allylic amide products, but in certain cases, the Pd−C bond can be trapped to achieve 1,2-difunctionalization of the alkene, including carboamination and aminoacetoxylation. Mechanistic studies have provided a variety of fundamental insights into the reactions, including the effect of ancillary ligands on palladium catalysts, the origin of the Bronsted-base-induced switch in regioselectivity in the oxidative amination of styrene, and evidence t...

Abstract: The last several years have produced some key advances in the area of alkene and alkyne metathesis by high oxidation state alkylidene and alkylidyne complexes along with new applications in organic and polymer chemistry. In this review we cover some of these developments and applications. The first part of this review concerns developments in catalyst synthesis and new catalysts. The second part concerns notable applications in organic and polymer chemistry. We discuss only high oxidation state alkylidene and alkylidyne chemistry of relevance to alkene or alkyne metathesis reactions and favor studies in the homogeneous phase.

Abstract: A cationic phosphinegold(I)-catalyzed intramolecular [2 + 2]-cycloaddition between an allene and an alkene to form alkylidene−cyclobutanes is described. Additionally, the reported cycloisomerization reaction provides access to enantioenriched bicyclo-[3.2.0] structures using chiral biarylphosphinegold(I) complexes as catalysts.

Abstract: The electrophilic activation of alkenes by transition-metal catalysts is a fundamental step in a rapidly growing number of catalytic processes. Although palladium is the best known metal for this purpose, the special properties of its third-row cousin platinum (strong metal-ligand bonds and slow substitution kinetics) have enabled the development of transformations that are initiated by addition to the C=C bonds by protic carbon, nitrogen, oxygen, and phosphorus nucleophiles, as well as alkene or arene nucleophiles. Additionally, reactivity profiles, which are often unique to platinum, provide wholly new reaction products. This Review concerns platinum-catalyzed electrophilic alkene activation reactions, with a special emphasis on the mechanistic properties of known systems, on the differences between platinum and palladium catalysts, and on the prospects for the development of new systems.

Abstract: Nitrogen-containing heterocyclic systems have attracted considerable interest over the years because they form the core structures, and are key intermediates, of natural products.[1] One of the most appealing synthetic approaches for their preparation is the intramolecular hydroamination of alkenes, in which the nitrogen–carbon bond is formed by addition of an amine to an olefin.[2] Various catalysts have been used to effect this transformation, which include alkali metals,[3] early[4] and late transition metals,[5] and f-block elements.[6] Interestingly, despite the buffering effect of amines, intramolecular[7] and even intermolecular[8] acid-catalyzed hydroaminations have recently been developed. Schlummer and Hartwig[7a] reported the cyclization of amino alkenes bearing an electron-withdrawing group on the nitrogen atom by catalysis with triflic or sulfuric acid (20 mol %; Scheme 1). A mechanistic study of this process suggested that in contrast to similar transformations using various electrophiles as promoters (for example, iodine-,[9] bromine-,[10] and selenium-based electrophiles[11]), the first step was protonation of the amine, followed by intramolecular transfer of the proton to the double bond in the rate-determining step, and lastly trapping of the generated cation by the amino group. Accordingly, in the absence of electron-withdrawing groups on the nitrogen atom, the cyclization does not occur because of the excessive basicity of the amino group, which prevents the transfer of the proton to the olefin. Scheme 1 a) Schematic representation of acid-catalyzed intramolecular hydroamination; EWC = electron-withdrawing group, n = l,2. b) The hydroiminiumation reaction as a potential synthetic route to cyclic iminium salts A. c) CAAC/H+ salts A′, the precursors ... Imines are certainly less basic than amines, and therefore it was decided to investigate the feasibility of “hydroiminiumation” reactions, which would be an atom-economical route to cyclic iminum salts A (Scheme 1). Providing there is a bulky aryl substituent on the nitrogen atom and that there is a quaternary carbon atom in the position α to the aldiminium carbon atom, salts A′ are the direct precursors of stable cyclic alkyl amino carbenes (CAACs) B.[12] We have shown that CAACs can compete with N-heterocyclic carbenes (NHCs)[13] as ligands for transition-metal-based catalysts,[12a] and also allow the preparation of very low coordinate transition-metal centers.[12b] We report herein our preliminary results on the scope of the thermally induced hydroiminiumation reaction and its application to the synthesis of a variety of CAAC precursors. To establish the viability of this hydroiminiumation methodology, the synthesis of the previously reported CAAC/H+ compound 4a[12a] was chosen as an initial test. Deprotonation of aldimine 1a, derived from 2,6-diisopropyl-aniline (DippNH2) and cyclohexane carboxaldehyde, with lithium diisopropylamide (LDA) leads to the corresponding 1-aza-allyl anion, which readily reacts at room temperature with 3-bromo-2-methylpropene (or 3-chloro-2-methylpropene) to afford the alkenyl aldimine 2a in 94% yield (Scheme 2). Addition of a stoichiometric amount of a 2M solution of HCl/Et2O to a toluene solution of 2a at −78 °C resulted in the immediate formation of a white precipitate. After 15 minutes at −78 °C, the mixture was allowed to warm to room temperature and stirring was continued for an additional 15 minutes. After filtration and recrystallization from chloroform, a new compound 3a was isolated as white crystals in 92% yield. The ionic character of 3a was apparent from its low solubility in toluene, while its acyclic nature was revealed by the presence of a 13C NMR signal at δ = 117.0 ppm from an ethylenic CH2 fragment. The protonation of the nitrogen atom was indicated by a 1H NMR signal at δ = 15.5 ppm, and by the deshielding of the N=CH 13C and 1H NMR signals (2a: (δ = 173.6 and 7.6 ppm; 3a: (δ = 189.8 and 8.0 ppm). A single-crystal X-ray diffraction study unambiguously proved the alkenyl aldiminium structure of 3a (Figure 1). [14] Pleasingly, it was noted that heating an aceto-nitrile solution of 3a in a tube sealed by a teflon stopcock at 50 °C for 18 h afforded the desired cyclic iminium salt 4a in 88% yield. Obviously, the last two steps of the synthesis (2a→4a) can be performed in situ, and the best results (88% yield of isolated product) were obtained when a twofold excess of HCl was used. The overall transformation (1a→4a) can thus be done in 83% yield, which compares extremely favorably with the previously reported method (48 % yield); moreover, the new route uses the same precursor 1a, but avoids the use of the costly reagents 1,2-epoxy-2-methylpropane and trifluoromethane sulfonic anhydride. Figure 1 Molecular structure of 3a in the solid state. Scheme 2 Influence of the nature of the R and R1 substituents on the rate of the hydroiminiumation reaction; Dipp = 2,6-iPr2C6H3; Mes = 2,4,6-Me3C6H2. [a] Time and temperature required for complete conversion of 3. [b] Yield of isolated product, without isolation ... To study the influence of various steric and electronic factors on the hydroiminiumation reaction, several different alkenyl aldimines 2b–h were prepared (Schemes 2, ​,3,3, and ​and4).4). Without exception, the protonation occurred smoothly at the nitrogen atom, and the ensuing alkenyl aldiminium salts 3b–h were obtained in good to excellent yields. The cyclization process occurs slightly more easily when bulky substituents are used on both sides of the NCC fragment (Scheme 2). Indeed, when two methyl groups were used in place of the cyclohexyl group of 3a, the formation of 4b required 24 h at 50 °C, whereas for derivative 3c (Ar = Mes, CR1R1 = CMe2) 24 h at 70 °C are necessary to achieve complete conversion. Not surprisingly, a limitation to the methodology was found when an electron-donating tert-butyl group was placed on the nitrogen atom. Here, because of the high basicity of the nitrogen center, no trace of the cyclic iminium salt 4d was detected when a toluene solution of 3d was heated at 110°C for 24 h. Scheme 3 Influence of the nature of the alkene substituents R1 and R2 on the rate and regioselectivity of the hydroiminiumation reaction. Tos=toluene-4-sulfonyl. [a] Time and temperature required for complete conversion of 3. [b] Yield of isolated product, without ... Scheme 4 Synthesis of six-membered heterocyclic aldiminium salt 4h. Use of alkenyl aldiminium salts 3a and 3e–g allowed study of the influence of the substitution pattern of the carbon–carbon double bond on the fate of the hydroiminiumation reaction, especially with regard to its regioselectivity (Scheme 3). The temperature required for cyclization was found to increase along the series 3a<3e<3f<3g. More importantly, in all cases five-membered heterocycles 4 resulting from exo cyclization were obtained, with no trace of the six-membered-ring isomers being detected. Strikingly, the cyclization of 3g affords exclusively five-membered heterocycle 4g (Figure 2), despite the presence of a phenyl group at the terminal carbon atom of the olefin, which would be expected to stabilize a benzylic carbocation intermediate. Together these observations favor a mechanism in which the proton would be transferred intramolecularly to the double bond in the rate-determining step, similarly to the mechanism proposed by Schlummer and Hartwig for the acid-catalyzed hydroamination reaction.[7a] When compared to the latter reaction involving alkenyl amine I, for which the formation of the six-membered ring II was observed, our result suggests that the addition of N—H across the double bond has a greater “concerted” character[15] in the hydroiminiumation than in the hydroamination reaction.[7a] Figure 2 Molecular structures of 3g (left) and 4g (right) in the solid state. Six-membered heterocyclic aldiminium salts can also be accessed as shown by the preparation of 4h (Scheme 4). However, as observed in the hydroamination reaction,[7a] the cyclization to 4h is more difficult than for the homologous five-membered ring 4e. Besides the easy preparation of a wide variety of CAAC/H+ compounds, the intramolecular hydroiminiumation reported here features some distinct advantages when compared to the intramolecular hydroamination reaction. The resulting iminium ions are very reactive, potentially allowing for the subsequent addition of a large range of nucleophiles, and since they are often prochiral, this chemistry offers the possibility of facile construction of a new stereogenic center a to the nitrogen atom. The extension of this work to other protonated sp2-nitrogen-containing species is under active investigation.

Abstract: Catalyzed movement of alkene double bonds up to 30 positions has been accomplished using a catalyst featuring a cationic CpRu fragment and bifunctional imidazolylphosphine. The basic nitrogen of the latter is thought to deprotonate coordinated alkene intermediates reversibly, facilitating isomerization between terminal and (E)-alkenes and accelerating conversions by factors of up to 1 × 104.

Abstract: A number of different PdII catalyst systems have been reported recently for the Wacker-type aerobic oxidative cyclization of alkenes bearing tethered nitrogen nucleophiles. This study examines the stereochemistry of the aminopalladation step with five different catalyst systems: Pd(OAc)2/DMSO (A), PdX2/pyridine [X = OAc (B), O2CCF3 (C)], Pd(IMes)(O2CCF3)2(OH2) (D), and Pd(O2CCF3)2/(−)-sparteine (E). Use of a stereospecifically deuterated cyclopentene substrate reveals that four of the five catalyst systems (A, B, C, and E) promote exclusive cis-aminopalladation of the alkene, whereas both cis- and trans-aminopalladation occur with the N-heterocyclic-carbene (NHC) catalyst system. If stoichiometric Bronsted base (NaOAc, Na2CO3) is added to the latter reaction conditions, however, only cis-aminopalladation is observed. The identity of the nitrogen nucleophile also affects the aminopalladation pathway, with results ranging from exclusively cis- to exclusively trans-aminopalladation. These results have impor...

Abstract: We report a novel copper(II)-catalyzed aminohydroxylation in which both heteroatoms of an N-sulfonyl oxaziridine are added across an alkene in a regioselective fashion. A variety of styrenes and electron-rich alkenes can be aminohydroxylated using this protocol. Preliminary investigations indicate that this new process is a rare non-oxenoid reaction of N-sulfonyl oxaziridines, involving a stepwise, polar mechanism rather than a concerted process.

Abstract: Phosphine-catalyzed reactions of electron-deficient alkenes have emerged as powerful tools for the preparation of biologically and medicinally useful compounds1,2 Common to these transformations is the generation of a putative dipolar phosphonium enolate through the addition of a tertiary phosphine to an electrophilic alkene Focusing on the use of allenoates as substrates, we have explored the various reactions available for the key zwitterionic intermediates and have developed new methods for the syntheses of tetrahydropyridines, dihydropyrroles, dioxanes, and pyrones3 In those studies, the reaction pathways of the proposed intermediates could be controlled by varying the nature of the electrophile4 or the structure of the initial zwitterionic adduct by using a bulky phosphine3d Although this approach has proved fruitful, leading to the discovery of an array of new reactions, we and others have never directly observed any of the conjectured zwitterionic intermediates5 Given the pivotal mechanistic roles played by phosphonium enolate intermediates, knowledge of their structures and reactivities will greatly benefit the further development of phosphine-catalyzed reactions Herein, we report the syntheses of stable tetravalent phosphonium enolates through simple one-pot, three-component processes and the X-ray crystallographic characterization of these dipolar intermediates Structural studies of tetravalent phosphonium zwitterions are complicated by the ability of their phosphorous atoms to adopt multiple valence structures In particular, β-phosphonium enolates arising from the addition of trivalent phosphines to α,β-unsaturated carbonyl compounds are unstable and exist mainly as isomeric pentavalent phosphoranes (eqs 1 and 2)6 For this reason, whereas a number of 1,2-λ5-oxaphospholenes have been characterized well,7 direct observation of tetravalent phosphonium enolates has remained an elusive goal, even though the mechanistic implications for various phosphine-catalyzed processes would be immense8 Following our interest in the chemistry of vinyl phosphonium enolates (eq 2) vis-a-vis that of alkyl derivatives (eq 1),2, 3 we pondered the reactivity of a further type of vinyl phosphonium zwitterion: one derived from an electron-deficient alkyne (eq 3) We were particularly intrigued to examine its potential to undergo addition to an aldehyde—and to determine the structure of any such adduct We were pleased to find that the three-component coupling reaction of PMe3, methyl phenylpropiolate, and 4-pyridinecarboxaldehyde proceeded smoothly in THF at room temperature to provide yellow crystals of a 1:1:1 adduct 1a (R = Me; R′ = Ph) in 83% yield (eq 4, Table 1) The 1H, 13C, and 31P NMR spectral data of 1a suggested a dipolar structure Most notably, the 31P NMR spectrum exhibited a diagnostic signal for tetravalent phosphorus at +160 ppm (entry 1)9 The reaction of PBu3 provided a similar dipolar adduct 1b (31P NMR: δ= +322 ppm) in 91% yield under otherwise identical reaction conditions (entry 2) This reaction proved to be a general one for a range of methyl propiolates of varying steric and electronic nature (entries 2–5) Table 1 Synthesis and structural data of phosphonium enolate zwitterions 1 The X-ray crystallographic data for 1a reveals that the phosphorous atom exists in a tetrahedral geometry and does not bond covalently with the enolate oxygen atom, as evidenced by the P1–O5 distance of 2821 A (Figure 1)10,11 The C3–C4 and C4–O5 bonds (1393 and 1271 A, respectively) both possess partial double bond character, with the negative charge dispersed mainly between the C3 and O5 atoms Although the carbomethoxy group appears to contribute to the delocalization of the negative charge only to a small degree, as indicated by the C3–C6 and C6–O7 bond lengths (1440 and 1230 A, respectively), its near in-plane orientation with the enolate (C4–C3–C6–O7 dihedral angle: 17574°) suggests a possible means of stabilization of the dipolar structure Figure 1 ORTEP depiction of 1a (50% thermal ellipsoids) The crystals of 1b and 1f contained pairs of conformationally distinct non-interacting zwitterions in each unit cell The distances between the P1 and O5 atoms in the pair of 1b zwitterions (2947 and 2941 A, respectively) reflect the increased steric bulk around the phosphorus center of 1b relative to that in 1a Again, the negative charge is localized on each C3–C4–O5 enolate moiety In fact, in one of the two conformations, the ester is twisted out of conjugation from the enolate (C4–C3–C6–O7 dihedral angle: 14684°; Table 1, entry 2) The more electron deficient phosphonium center in 1f resides closer to the oxygen atom than that in 1a, despite the increased steric bulk around the phosphorus atom (P1–O5 distances in 1f: 2597 and 2620 A, respectively) Our X-ray crystallographic analyses of 1a, 1b, and 1f provide the first direct experimental proof of the tetravalency of phosphorus atoms in phosphonium enolate zwitterions; previously, evidence for their structures was implied from NMR and IR spectroscopic data8 We construe that the presence of electron-donating alkyl groups on the phosphonium centers in our zwitterions decreases their impetus for conversion to pentavalent phosphoranes Indeed, a number of stable oxaphospholenes have been isolated containing three aryl substituents on pentavalent phosphorus atoms12 Accordingly, we turned our attention to zwitterionic systems containing one or more aryl substituents on their phosphorus atoms We isolated zwitterions 1f and 1g from the reactions of PMe2Ph with methyl phenylpropiolate and PMePh2 with methyl propiolate, respectively (Table 1, entries 6 and 7) The reaction of PMePh2 with methyl phenylpropiolate did produce a zwitterion that was observable in solution (NMR spectroscopy), but not isolable (entry 8) In contrast, the reactions of PPh3 did not provide any detectable zwitterions (entries 9 and 10)13 These results are consistent with our hypothesis that electron-releasing alkyl substituents on the phosphonium center play a critical role in stabilizing phosphonium enolate zwitterions We propose that zwitterion 1 is formed through conjugate addition of the phosphine to the propiolate and subsequent nucleophilic addition of the vinyl anion 2 to 4-pyridinecarboxaldehyde (Scheme 1)14 The resulting zwitterion 3, upon proton transfer, forms the ylide 4 Another proton transfer process affords the zwitterion 115 Scheme 1 Proposed mechanism for the formation of 1 This paper describes the synthesis of stable phosphonium enolate zwitterions, which have been proposed as intermediates in Morita–Baylis–Hillman (MBH) reactions, through novel three-component coupling reactions between tertiary phosphines, alkynoates, and aldehydes We report, for the first time, the isolation and X-ray crystallographic characterization of such phosphonium enolate zwitterions, establishing the tetravalent nature of their phosphorous atoms unequivocally These structures, which stand in contrast to those of the well-established pentavalent 1,2-λ5-oxaphospholenes, might explain the instability and high reactivity of phosphonium enolate zwitterions in MBH-type reactions Our future efforts will focus on exploring the synthetic utility of zwitterions 1 and on extending this study to novel catalytic processes involving phosphonium enolates

Abstract: This account summarizes our attempts to develop metal-catalyzed asymmetric syntheses of P-stereogenic phosphines. While such phosphines undergo pyramidal inversion slowly at room temperature, inversion is rapid in metal-phosphido com-plexes (M-PR 2 ). These observations were the basis for catalytic, dynamic kinetic resolution processes in which racemic secondary phosphines [PR(R′)H] were converted into enantioenriched tertiary phosphines [PR(R′)(R′′)] by platinum-catalyzed asymmetric hydrophosphination of acrylonitrile or related Michael acceptors, by -palladium-catalyzed asymmetric phosphination of aryl iodides using secondary phosphines or phosphine-boranes, and by platinum-catalyzed asymmetric alkylation of secondary phosphines. The key intermediates were diastereomeric phosphido complexes with chiral ancillary ligands (L n *-M-PRR′). Their relative rates of P-inversion and phosphorus-carbon bond formation controlled the enantioselectivity of product formation, whether the phosphorus-carbon bonds were formed by reductive elimination (for Pd), or by the reaction of a platinum-phosphido complex with an electrophile (an alkene in hydrophosphination, or a benzyl bromide in alkylation). The results of mechanistic studies and their use in the design of improved catalytic reactions are described. 1 Introduction 2 Phosphorus Inversion 3 Platinum-Catalyzed Asymmetric Hydrophosphination 4 Palladium-Catalyzed Asymmetric Phosphination 4.1 Secondary Phosphines 4.2 Secondary Phosphine-Boranes 5 Platinum-Catalyzed Asymmetric Alkylation of Secondary Phosphines 6 Conclusion

Abstract: The first catalytic method for the efficient conversion of epoxides to succinic anhydrides via one-pot double carbonylation is reported. This reaction occurs in two stages: first, the epoxide is carbonylated to a β-lactone, and then the β-lactone is subsequently carbonylated to a succinic anhydride. This reaction is made possible by the bimetallic catalyst [(ClTPP)Al(THF)2]+[Co(CO)4]- (1; ClTPP = meso-tetra(4-chlorophenyl)porphyrinato; THF = tetrahydrofuran), which is highly active and selective for both epoxide and lactone carbonylation, and by the identification of a solvent that facilitates both stages. The catalysis is compatible with substituted epoxides having aliphatic, aromatic, alkene, ether, ester, alcohol, nitrile, and amide functional groups. Disubstituted and enantiomerically pure anhydrides are synthesized from epoxides with excellent retention of stereochemical purity. The mechanism of epoxide double carbonylation with 1 was investigated by in situ IR spectroscopy, which reveals that the t...

Abstract: [reaction: see text] The iridium catalyst [Ir(Cp*)Cl2]2 is effective for the rearrangement of oximes to furnish amides. The reaction has been combined with catalytic transfer hydrogenation between an alcohol and alkene to allow the conversion of alcohols into amides in a one-pot process.

Abstract: A novel site-specific structure−activity relationship was developed for the site-specific addition of OH radicals to (poly)alkenes at 298 K. From a detailed structure−activity analysis of some 65 known OH + alkene and diene reactions, it appears that the total rate constant for this reaction class can be closely approximated by a sum of independent partial rate constants, ki, for addition to the specific (double-bonded) C atoms that depend only on the stability type of the ensuing radical (primary, secondary, etc.), that is, on the number of substituents on the neighboring C atom in the double bond. The (nine) independent partial rate constants, ki, were derived, and the predicted rate constants (kOH,pred = Σki) were compared with experimental kOH,exp values. For noncyclic (poly)alkenes, including conjugated structures, the agreement is excellent (Δ < 10%). The SAR-predicted rate constants for cyclic (poly)alkenes are in general also within <15% of the experimental value. On the basis of this SAR, it is p...

Abstract: Cr2O3/ZrO2 nano-composite catalysts modified with Ni, Fe, Co, Mn oxides respectively were synthesized by coupling co-precipitation with azeotropic distillation method. The effect of modifiers on the catalytic activity in the dehydrogenation of ethane with CO2 was investigated. The modifiers exhibited different effects on catalytic behavior. Fe, Co and Mn oxides markedly increased ethylene selectivity, but the Ni-5-Cr-10/Zr nano-composite catalyst mainly favored side reactions-the reforming and cracking reactions. The Fe-5-Cr-10/Zr nano-composite catalyst exhibited an excellent performance in this reaction, producing 50.05% ethylene yield at 53.72% ethane conversion at 650 degrees C. The modified Cr2O3/ZrO2 nanocomposite catalysts were characterized by BET, TEM, XRD, XPS, CO2-TPD and NH3-TPD techniques. The characterization indicated that weak acid sites are involved in ethane activation, and strong acid-base pairs promote the reforming and cracking reactions. The distribution of chromium species, oxygen species and base/acid property on the surface of catalyst cooperatively determined the catalytic activity in dehydrogenations of ethane to ethylene using CO2 as an oxidant. (c) 2007 Elsevier B.V. All rights reserved.

Abstract: A general and efficient method for the rhodium-catalyzed enantioselective catalytic conjugate addition of organoboronic acids to alpha,beta-unsaturated sulfones is described. The success of the process relies on the use of alpha,beta-unsaturated 2-pyridyl sulfones as key metal-coordinating substrates; typical sulfones such as vinyl phenyl sulfones are inert under the reaction conditions. Among a variety of chiral ligands, Chiraphos provided the best asymmetric induction. This rhodium [Rh(acac)(C2H4)2]/Chiraphos catalyst system has a broad scope, being applicable to the addition of both aryl and alkenyl boronic acids to cis and trans alpha,beta-unsaturated 2-pyridyl sulfones. In most cases, especially in the addition of aryl boronic acids, the reactions take place cleanly and with high enantioselectivity, affording chiral beta-substituted 2-pyridyl sulfones in good yields and enantioselectivities (70-92% ee). The sense and magnitude of this enantioselectivity have been studied by DFT theoretical calculations of the aryl-rhodium insertion step. These calculations strongly support the formation of a five-membered pyridyl-rhodium chelated species as the most stable complex after the insertion into the C=C bond. These highly enantioenriched chiral sulfones are very appealing building blocks in enantioselective synthesis. For instance, the straightforward elimination of the 2-pyridylsulfonyl group by either Julia-Kociensky olefination or alkylation/desulfonylation sequences provides a variety of functionalized chiral compounds, such as allylic substituted alkenes or beta-substituted ketones and esters.

Abstract: In situ combination of diphosphinic amides and Zr(NMe(2))(4) results in the formation of chiral zirconium bis(amido) complexes. The complexes are competent catalysts for intramolecular asymmetric alkene hydroamintion, providing piperidines and pyrrolidines in up to 80% ee and high yield. This system utilizes an inexpensive zirconium precatalyst and readily prepared ligands and is the first asymmetric alkene hydroamination catalyst based upon a neutral zirconium bis(amido) complex.

Abstract: We report a highly regioselective PdII-catalyzed reductive coupling of an alkene with an organostannane using a tandem alcohol oxidation under aerobic conditions. Both aryl- and vinylstannanes are competent coupling partners with a variety of styrene derivatives. Mechanistic experiments support a tandem alcohol oxidation/alkene functionalization process. The ability to trap a palladium hydride derived from alcohol oxidation with an alkene provides a fundamentally different approach to cross-coupling reactions.

Abstract: By detailed study of the possible side reactions in the previously reported aziridination of alkenes with N-aminoheterocycles mediated by hypervalent iodine reagents, the requirements to make this reaction catalytic in iodoarene have been determined The reaction requires an oxidant that will oxidise iodoarenes but that does not oxidise alkenes, but it is possible that no such oxidant actually exists! A method in which the hypervalent iodine reagent can be recycled without the need for reisolation is possible Further study into the mechanism of this reaction gives tentative evidence that the reaction proceeds through formation of an aminoiodane that reacts directly with the alkene, contrary to previous literature reports in which an acetoxyamine intermediate is suggested The temperature effect of this reaction is remarkable

Abstract: This thesis describes the development of new catalytic methods for the synthesis and application of organometallic reagents, mainly focusing on allylboronic acid derivatives. Thus, palladium pincer-complex catalysis has been applied for extending the scope of palladiumcatalyzed borylation reactions in the synthesis of regio- and stereodefined functionalized allylboronic acid derivatives. These novel allylboronic acids were also employed as substrates in palladium catalyzed regioselective coupling reactions with iodobenzenes. We have also developed a new one-pot sequence based on preparation of allyl- and vinylboronates via catalytic carbon-hydrogen bond activation/borylation reactions. The synthetic scope of the reaction as well as mechanistic studies on the borylation process are presented. Finally, the synthesis of new chiral palladium pincer-complexes is described. These species were employed as catalysts in asymmetric electrophilic allyation of imines.