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The accurate prediction of the basicity of tertiary phosphines in acetonitrile and water is reported by the linear correlation between computed Δp

A non-planar triarylborane and a new member of the boratriptycene family bearing a selenium atom in bridgehead position of triptycene scaffold was generated and isolated as a boron-‘ate’ complex paired with a weakly coordinating anion. With similar electronegativity while possessing longer atom radius with respect to sulfur, the introduction a selenium atom, in the form of a selenenium moiety, at the bridgehead of a triptycene scaffold allows a very precise modification of the pyramidalization of the boron atom environment. Experimental and computational evaluation of the Lewis acidity of this new boratriptycene derivative gave qualitative information on how a modification of the pyramidalization of the boron environment affects alone Lewis acidity parameters of such pyramidal triarylborane.

Isolation and characterization of highly reactive intermediates are crucial to understand the nature of chemical reactivity. Accordingly, the reactivity of weakly coordinating anions (WCA), usually used to stabilized cationic super electrophiles are of fundamental interest. When a variety of WCA are known to form stable σ-complexes with a proton, inducing Brønsted super acidity, bis-coordinated weak-coordinated anions are much more elusive and considered as long-sought reactive species. In this work, the chemistry of borylated sulfate, triflimidate and triflate anions where scouted in details with the aim of synthetizing the unique analogs of protonated Brønsted superacids. Those complexes were formed by successive borylation with a 9-boratriptycene derived Lewis super acid paired with a weak coordinated anion, characterized in solution and in the solid state and exhibit unique structures and reactivities.

The association of pyridine and of 2,4,6-trimethylpyridine (collidine) with a pyramidal triarylborane belonging to the 9-boratriptycene family is investigated by NMR spectroscopy and by X-ray diffraction analysis. Despite of the large size of the ortho-disubstituted collidine Lewis base and of the large steric hindrance of the boron Lewis superacid used (9-boratriptycene-10-sulfonium), the superacidity at its boron atom is enabling the formation of a B-N bond and is resulting in a very stabe Lewis adduct. Single- crystal X-ray diffraction analysis revealed an exceptional deformation of the collidine moiety with a deviation from planarity of nearly 41° between the pyridine C−N bonds and the ortho-methyl groups C−Me bonds, which is even resulting a small twist of the collidine six-membered heteroaromatic ring into a boat-like conformation. Computational investigations indicate that the steric repulsions are reducing the Gibbs free energy of Lewis adduct formation by approximately 50 kJ mol−1.

The activation or heterolytic splitting of methane, a challenging substrate usually restricted to transition metals, has so far proven elusive in experimental frustrated Lewis pair (FLP) chemistry. In this article, we demonstrate, using density functional theory (DFT), that 1-aza-9-boratriptycene is a conceptually simple intramolecular FLP for the activation of methane. Systematic comparison with other FLP systems allows to gain insight into their reactivity with methane. The thermodynamics and kinetics of methane activation are interpreted by referring to the analysis of the natural charges and by employing the distortion-interaction/activation strain (DIAS) model. These showed that the nature of the Lewis base influences the selectivity over the reaction pathway, with N Lewis bases favoring the deprotonation mechanism and P bases the hydride abstraction one. The lower barrier of activation for 1-aza-9-boratriptycene and the higher products stability are due to a better interaction energy than its counterparts, itself due to electrostatic interactions with the methane moiety, favorable orbital overlaps allowed by the side-attack, and space proximity between the B and N atoms.

This article highlights the recent work of M. Wagner and collaborators on the synthesis, bridgehead functionalization, and photoisomerization of boron-doped triptycene derivatives (https://doi.org/10.1039/D3SC00555K).

The latest developments in the field of electrophilic C−H borylation reactions of arenes and heteroarenes without transition metals are briefly overviewed, with a particular emphasis on the latest advances enabling the highly regioselective C−H borylations of indoles and indolines using borylation template reagents.

We developed two synthetic strategies towards triptycene-derived bulky boranes, boronates, and boron ate-complexes. Starting from borylated or brominated anthracenes and using a Br/Li exchange and [4+2] cycloaddition reaction with in-situ generated benzyne, we produced a series of triptycene boronates and borates with various boron substituents in positions 1 and 9, such as BPin, Bneo, BF3K and B(Mes)2. Single-crystal X-ray diffraction analysis and UV-Vis/photoluminescence measurements provided quantitative information on the effect of the triptycene scaffold on the photophysical and electronic properties of the obtained compounds.

ortho-Substituted and unsymmetrical 9-phospha-triptycenes were synthesizedviatwo synthetic approaches involving densely functionalizedortho-halogenated triarylmethane or phosphine precursors.ortho-Substituents imposed a considerable steric shielding due to the tricyclic cage-shaped structure with the aryl rings p-systems orthogonal to the phosphorus electron pair. A series of Au(i) and Rh(i) complexes were analysed in the solid state to determine Tolman electronic parameters, cone angles and buried volumes of these unprecedented functionalized phosphines. Quantum chemical calculations of electronic and steric descriptors revealed that these cage-shaped phosphines are electron-poor and that single methyl substituent is enough to provide the largest effect on steric shielding reported so far in triarylphosphines. An unsymmetrically substituted 9-phosphatriptycene was resolved by chiral HPLC, opening the avenue towards stableP-chirogenic triarylphosphines with unlimited configurational stability for new catalyst development in asymmetric transition-metal catalysis.

A highly bent triarylborane, 9-boratriptycene, was generated in solution by selective protodeboronation of the corresponding tetra-aryl boron ate complex with the strong Brønsted acid HNTf2. The iptycene core confers enhanced Lewis acidity to 9-boratriptycene, making it unique in terms of structure and reactivity. We studied the stereoelectronic properties of 9-boratriptycene by quantifying its association with small N- and O-centered Lewis bases, as well as with sterically hindered phosphines. The resultant Lewis adducts exhibited unique structural, spectroscopic, and photophysical properties. Beyond the high pyramidalization of the 9-boratriptycene scaffold and its low reorganization energy upon Lewis base coordination, quantum chemical calculations revealed that the absence of π donation from the triptycene aryl rings to the boron vacant pz orbital is one of the main reasons for its high Lewis acidity.

Although boron Lewis acids commonly adopt a trigonal planar geometry, a number of compounds in which the trivalent boron atom is located in a pyramidal environment have been described. This review will highlight the recent developments of the chemistry and applications of non-planar boron Lewis acids, including a series of non-planar triarylboranes derived from the triptycene core. A thorough analysis of the properties and of the influence of the pyramidalization of boron Lewis acids on their stereoelectronic properties and reactivities is presented based on recent theoretical and experimental studies.1 Non-planar Trialkylboranes2 Non-planar Alkyl and Aryl-Boronates3 Non-planar Triarylboranes and Alkenylboranes3.1 Previous Investigations on Bora Barrelenes and Triptycenes3.2 Recent Work on Boratriptycenes from Our Research Group4 Applications of Non-planar Boranes4.1 Non-planar Alkyl Boranes and Boronates4.2 Non-planar Triarylboranes (Boratriptycenes)5 Other Non-planar Group 13 Lewis Acids6 Further Work and Perspectives

The frustrated Lewis pair-catalyzed hydrogenation of unactivated alkenes with H2 is reported. The weak Lewis basicity and high steric hindrance of ortho-substituted 9-phosphatriptycene derivatives is taken as an advantage to catalyze this reaction in combination with tris(pentafluorophenyl)borane. A scope of unsaturated substrates is described. The thermodynamics and kinetics of hydrogenation investigated by density functional theory show that the protonation of the olefin by the strongly acidic phosphonium cation is the critical step of the reaction.

The rational design of a geometrically constrained boron Lewis superacid featuring exceptional structure and reactivity is disclosed. It enabled the formation of non-classical electron deficient B−H−B type of bonding, which was supported by spectroscopic and structural parameters as well as computational studies. Taming the pyramidal Lewis acid electrophilicity through weak coordinating anion dissociation enabled a series of highly challenging chemical transformations, such as Csp2−H and Csp3−H activation under a frustrated Lewis pair regime and the cleavage of Csp3−Si bonds. The demonstration of such rich chemical behaviour and flexibility on a single molecular compound makes it a unique mediator of chemical transformations generally restricted to transition metals.

This chapter offers an overview of the development of the chemistry of four-membered rings with one phosphorus, arsenic, antimony, or bismuth Atom in the period between 2008 and 2018. In this context, synthesis, structural, reactivity, and computational aspects of these heterocycles are covered.

The chapter summarizes the development in the field of six-membered rings with one phosphorus atom in the period between 2008 and 2018. In this context, theoretical, structural, thermodynamic, and reactivity aspects of aromatic and non-aromatic phosphorus-based heterocycles are covered and discussed. ispartof: Comprehensive Heterocyclic Chemistry IV pages:685-717 ispartof: vol:7 pages:685-717 status: Published online

Bending the planar trigonal boron center of triphenylborane by connecting its aryl rings with carbon or phosphorus linkers gave access to a series of 9-boratriptycene derivatives with unprecedented structures and reactivities. NMR spectroscopy and X-ray diffraction of the Lewis adducts of these non-planar boron Lewis acids with weak Lewis base revealed particularly strong covalent bond formation. The first Lewis adduct of a trivalent boron compounds with the Tf 2N − anion illustrates the unrivaled Lewis acidity of these species. Increasing the pyramidalization of the boron center and using a cationic phosphonium linker resulted in an exceptional enhancement of Lewis acidity. Introduction of a phosphorus and a boron atom at each edge of a triptycene framework, allowed access to new bifunctional Lewis acid-base 9-phospha-10-boratriptycenes featuring promising reactivity for the activation of carbon-halogen bonds.

Fast I/Sm and Br/Sm exchanges take place whenvarious aromatic or heterocyclic iodides and bromides aretreated with nBu2SmCl·4LiCl and nBu3Sm·5LiCl, respectively.The resulting organosamarium reagents were efficientlyquenched with aldehydes, ketones, and imines. Also, theyundergo acylations when treated with N,N-dimethylamidesleading to ketones. The rate of the Br/Sm exchange for a typicalaryl bromide was determined and found to be 8.5 x 105 fasterthan the Br/Mg exchange, indicating that the rate of a metalexchangeis related to the ionic character of the carbon–metalbond and to the metal electronegativity., Fast I/Sm and Br/Sm exchanges take place when various aromatic or heterocyclic iodides and bromides are treated with nBu2SmCl·4LiCl and nBu3Sm·5LiCl, respectively. The resulting organosamarium reagents were efficiently quenched with aldehydes, ketones, and imines. Also, they undergo acylations when treated with N,N-dimethylamides leading to ketones. The rate of the Br/Sm exchange for a typical aryl bromide was determined and found to be 8.5 x 105 faster than the Br/Mg exchange, indicating that the rate of a metalexchange is related to the ionic character of the carbon–metal bond and to the metal electronegativity.

Two straightforward synthetic methods towards semi‐planar triarylboranes with two aryl rings connected by a methylene bridge have been developed. The fine‐tuning of their stereoelectronic properties and Lewis acidities was achieved by introducing fluorine, methyl or methoxy groups either at their exocyclic or their bridged aryl rings. X‐ray diffraction analysis and quantum‐chemical calculations provided quantitative information on the structural distortion experienced by the near planar hydro‐boraanthracene skeleton during the association with Lewis bases such as NH3 and F–. Though the methylene bridge between the ortho‐positions of two aryl rings of triarylboranes decreased the Gibbs free energies of complexation with small Lewis bases by less than 5 kJ mol‐1 relative to the classical Lewis acid BAr3, the steric shielding of the CH2 bridge is sufficient to avoid the formation of Lewis adducts with larger Lewis bases such as triarylphosphines. A newly synthesized spirocyclic amino‐borane with a long intramolecular B‐N bond that could be dissociated under thermal process, UV‐irradiation, or acidic conditions might be a potential candidate in Lewis pairs catalysis.

Several formal heteroborylative cyclization reactions have been recently reported, but little physical-organic and mechanistic data are known. We now investigate the catalyst-free formal thioboration reaction of alkynes to gain mechanistic insight into B-chlorocatecholborane (ClBcat) in its new role as an alkynophilic Lewis acid in electrophilic cyclization/dealkylation reactions. In kinetic studies, the reaction is second-order globally and first-order with respect to both the 2-alkynylthioanisole substrate and the ClBcat electrophile, with activation parameters of ΔG‡ = 27.1 ± 0.1 kcal mol-1 at 90 °C, ΔH‡ = 13.8 ± 1.0 kcal mol-1, and ΔS‡ = -37 ± 3 cal mol-1 K-1, measured over the range 70-90 °C. Carbon kinetic isotope effects supported a rate-determining AdE3 mechanism wherein alkyne activation by neutral ClBcat is concerted with cyclative attack by nucleophilic sulfur. A Hammett study found a ρ+ of -1.7, suggesting cationic charge buildup during the cyclization and supporting rate-determining concerted cyclization. Studies of the reaction with tris(pentafluorophenyl)borane (B(C6F5)3), an activating agent capable of cyclization but not dealkylation, resulted in the isolation of a postcyclization zwitterionic intermediate. Kinetic studies via UV-vis spectroscopy with this boron reagent found second-order kinetics, supporting the likely relevancy of intermediates in this system to the ClBcat system. Computational studies comparing ClBcat with BCl3 as an activating agent showed why BCl3, in contrast to ClBcat, failed to mediate the complete the cyclization/demethylation reaction sequence by itself. Overall, the results support a mechanism in which the ClBcat reagent serves a bifunctional role by sequentially activating the alkyne, despite being less electrophilic than other known alkyne-activating reagents and then providing chloride for post-rate-determining demethylation/neutralization of the resulting zwitterionic intermediate.

Kinetic and thermodynamic measurements of the ease of covalent hydration of 4-nitrobenzodifuroxan (NBDF) to give the corresponding hydroxy adduct has been carried out over a large pH range of 0.82–12.23 in aqueous solution. A most important result is that water is the sole efficient nucleophile contributing to the hydration of this peculiar nitroolefin in the pH range 4–8. Based on this finding as well as a pK a H2O value of 2.85 for the complexation process there is no doubt that the electrophilic character of NBDF falls in the domain of superelectrophilicity defined with reference to covalent nucleophilic additions to 4,6-dinitrobenzofuroxan (DNBF; pK a H2O = 3.75) and related heterocycles. This also corresponds to a positioning of NBDF at the top of the electrophilicity scale E introduced by Mayr to describe the feasibility of nucleophilic-electrophilic combinations. Returning to the hydration of the series of activated olefins, it has been possible to expand the domain of reactivity of Michael acceptors by six orders of magnitude, going from benzylidenemalonitrile (pK a H2O = 10.70; E = –9.42) to the para-nitro-substituted benzylidene Meldrum’ s acid (pK a H2O = 3.46; E = –5.49). The positioning of these olefins on the pK a scale shows that not only 4-nitrobenzodifuroxan but also the unsubstituted Meldrum’s acid are located in the superelectrophilic region.

The structures of the covalent Lewis adducts and/or frustrated Lewis pairs derived from 2- and 2,6-substituted pyridines with diaryl (Ar2CH+) and with the more bulky triaryl (Ar3C+) carbenium ions were analyzed by UV-vis and NMR spectroscopy. Thermodynamics (equilibrium constants) and kinetics (rate constants) of the associations of the carbon-centered Lewis acids Ar2CH+ with a series of sterically hindered pyridines were investigated and used for the determination of the Lewis basicities and nucleophilicities, on the basis of the Mayr electrophilicity/nucleophilicity and Lewis acidity/basicity linear free energy relationships. In addition, methyl and benzhydryl cation affinities were computed to elucidate the respective steric and electronic contributions of the substituents to the nitrogen atom Lewis basicity. The influence of the size of the reference carbenium ion on the magnitude of the repulsion induced by the pyridine substituents (Me, tBu in 2- or 2,6-positions) was also analyzed. Cumulated steric repulsion was found to decrease the reactivity of the nitrogen atom by up to 10 orders of magnitude.

The nucleophilicity and Lewis basicity of sterically hindered phosphines, widely used in catalysis and in frustrated Lewis pair (FLP) chemistry, have been quantified by determining the rates and equilibrium constants of their associations with reference systems (benzhydrylium and tritylium ions) of calibrated electrophilicities and Lewis acidities. These structure-reactivity investigations allow a rationalization of the Lewis acid-base interactions all along the way from covalent Lewis adducts to FLPs. Comparisons of the association of phosphines of increasing sizes (Ph3 P, (o-tolyl)3 P, and tBu3 P) with the triarylborane B(C6 F5 )3 and with the isoelectronic tritylium ions Ar3 C+ provide detailed insights for the future fine-tuning of the reactivities of FLPs. As a proof of concept, tritylium-ion-derived FLPs were shown to react with alkynes, as reported for the FLPs derived from the benchmark triarylborane B(C6 F5 )3 .

Two practical and high-yielding syntheses of 9-phosphatriptycene are reported. In both approaches, the key step is based on the cyclization of a (tris)lithio-triphenylmethane or a (tris)lithio-triphenylphosphine intermediate on a phosphorus or a carbon electrophile, respectively. The association of 9-phosphatriptycene with representative boron- and carbon-centered Lewis acids was investigated by IR, NMR, and UV-vis titration experiments and by computational methods, shedding light on its steric hindrance, σ-donating ability, and Brønsted and Lewis basicities.

The isolation, characterization, and the first X-ray structures of a fluorenylium ion and its Lewis adducts with nitrogen- and phosphorus-centered Lewis bases are reported. Kinetics of the reactions of a series of fluorenylium ions with reference π-, σ-, and n-nucleophiles of various sizes and nucleophilicities allowed the interplay between electronic and structural parameters on the electrophilicities of these planarized tertiary carbenium ions to be elucidated. Structure-reactivity correlations and extensive comparisons of their reactivities with those of di- and triarylcarbenium ions are described. Quantitative determination of the electrofugalities of fluorenylium ions revealed to which extent they are complementing tritylium ions as protecting groups and how their tuning is possible. Determination of the equilibrium constants of the Lewis adducts formation between pyridines of calibrated Lewis basicities and phenylfluorenylium and tritylium ions allowed the determination of their Lewis acidities and to showcase the potential of these carbon-centered Lewis acids in catalysis.

Kinetics of activation of methyl and benzyl metallocene precatalysts by benzhydrylium ions, tritylium ions, and triarylborane B(C6 F5 )3 were measured spectrophotometrically. The rate constants correlate linearly with the electrophilicity parameter E of the benzhydrylium and tritylium ions employed, allowing us to determine the σ-nucleophilicities of the metal-carbon bond of several zirconocenes and titanocenes. Bridging, substitution, metal, and ligand effects on the rates of metal-alkyl bond cleavage (M=Zr, Ti) were studied and structure-reactivity correlations were used to predict the kinetics of generation of metallocenium ions pairs, which are active catalysts in polymerization reactions and are highly electrophilic Lewis acids in frustrated Lewis pair catalysis.

The chemical study of the stems extract of Psychotria arborea Hiern led to the isolation of thirteen compounds, including four anthraquinones: 2-methylanthracene-9,10-dione (1), 2-methoxyanthracene-9,10-dione (2), 2-hydroxy-3-methylanthracene-9,10-dione (3) and 3-hydroxy-1-methoxy-2-methylanthracene-9,10-dione (4); two diterpenes: ent-kaur-16-en-19-oic acid (5) and 15-acetoxy-ent-kaur-16-en-19-oic acid (6); two triterpenes, β-amyrin (8) and oleanolic acid (9), one flavonoid: Quercetin (7), three sterols: A mixture of stigmasterol (10) and β-sitosterol (11) and β-sitosterol-3-O-β-D-glucopyranoside (12) and one fatty acid (13). The structures of these compounds were elucidated based on NMR and HR-ESIMS analysis, further supported by comparison with previously reported spectral data. Compounds 1–4 and compounds 10–12 were tested for their antibacterial activity against three bacteria strains Escherichia coli, Staphylococcus aureus and Salmonella enterica. All these tested compounds were found to be inactive. Furthermore, the chemotaxonomic significance of the obtained compounds was discussed in detail.

Eight substituted aryl(indol-3-yl)methylium tetrafluoroborates 3(a-h)-BF4 and three bis(indol-3-yl)methylium tetrafluoroborates 3(i-k)-BF4 have been synthesized and characterized by NMR spectroscopy and X-ray crystallography. Their reactions with π-nucleophiles 8(a-j) (silylated enol ethers and ketene acetals) were studied kinetically using photometric monitoring at 20 °C. The resulting second-order rate constants were found to follow the correlation log k(20 °C) = sN(N + E), in which nucleophiles are characterized by the two solvent-dependent parameters N and sN, and electrophiles are characterized by one parameter, E. From the previously reported N and sN parameters of the employed nucleophiles and the measured rate constants, the electrophilicities of the indol-3-ylmethylium ions 3(a-k) were derived and used to predict potential nucleophilic reaction partners. A discrepancy between published rate constants for the reactions of morpholine and piperidine with the (2-methylindol-3-yl)phenylmethylium ion 3h and those calculated from E, N, and sN was analyzed and demonstrated to be due to a mistake of the value reported in the literature.

Boron-ate complexes derived from primary and secondary boronic esters and aryllithiums have been isolated, and the kinetics of their reactions with carbenium ions studied. The second-order rate constants have been used to derive nucleophilicity parameters for the boron-ate complexes, revealing that nucleophilicity increased with (i) electron-donating aromatics on boron, (ii) neopentyl glycol over pinacol boronic esters, and (iii) 12-crown-4 ether.

Boron ate complexes derived from thienyl and furyl boronic esters and aryllithium compounds have been isolated and characterized by X-ray crystallography. Products and mechanisms of their reactions with carbenium and iminium ions have been analyzed. Kinetics of these reactions were monitored by UV/Vis spectroscopy, and the influence of the aryl substituents, the diol ligands (pinacol, ethylene glycol, neopentyl glycol, catechol), and the counterions on the nucleophilic reactivity of the boron ate complexes were examined. A Hammett correlation confirmed the polar nature of their reactions with benzhydrylium ions, and the correlation lg k(20 °C)=sN (E+N) was employed to determine the nucleophilicities of the boron ate complexes and to compare them with those of other borates and boronates. The neopentyl and ethylene glycol derivatives were found to be 10(4) times more reactive than the pinacol and catechol derivatives.

Aus Thienyl- bzw. Furylboronsaureestern und Aryllithium-Verbindungen hergestellte Bor-at-Komplexe wurden isoliert und durch Rontgenstrukturanalyse charakterisiert. Die Produkte und Mechanismen ihrer Reaktionen mit Carbenium- und Iminium-Ionen wurden analysiert. Durch UV/Vis-spektroskopische Verfolgung der Kinetik dieser Reaktionen wurde der Einfluss der Aryl-Substituenten, der Diol-Liganden (Pinakol, Ethylenglykol, Neopentylglykol, Brenzkatechin) und der Gegenionen auf die nucleophile Reaktivitat der Bor-at-Komplexe untersucht. Eine Hammett-Korrelation bestatigte die polare Natur ihrer Reaktionen mit Benzhydrylium-Ionen, und die Korrelation lg k(20 °C)=sN(E+N) wurde verwendet, um die Nucleophilie der Bor-at-Komplexe zu bestimmen und mit der anderer Borate und Boronate zu vergleichen. Die Neopentylglykol- und Ethylenglykol-Derivate sind 104-mal reaktiver als die Pinakol- und Brenzkatechin-Derivate.

Secondary alkyllithium reagents bearing an OTBS group (TBS=tert-butyldimethylsilyl) at the 3-position can be prepared stereoconvergently through an I/Li exchange from a diastereomeric mixture of the corresponding secondary alkyl iodides. These lithium reagents react with a range of electrophiles, including carbon electrophiles, with retention of configuration to yield various 1,3-difunctionalized derivatives with good diastereoselectivities. Kinetic studies show that the 3-siloxy group strongly accelerates the epimerization at the lithium-substituted carbon atom. This method offers a new way to construct chiral open-chain molecules with excellent stereoselectivity.

In Position 3 mit einer OTBS-Gruppe funktionalisierte sekundare Alkyllithiumreagentien konnen stereokonvergent durch einen I/Li-Austausch aus einer Diastereomerenmischung der entsprechenden sekundaren Alkyliodide hergestellt werden. Diese Lithiumreagentien reagieren mit einer Bandbreite an Elektrophilen, einschlieslich Kohlenstoffelektrophilen, unter hoher Retention der Konfiguration und bieten Zugang zu verschiedenen 1,3-difunktionalisierten Derivaten mit guter Diastereoselektivitat. Kinetische Studien zeigen, dass die 3-Siloxygruppe die Epimerisierung des Lithium-substituierten Kohlenstoffatoms stark beschleunigt. Diese Methode bietet einen neuen Weg hin zu chiralen offenkettigen Molekulen mit exzellenter Stereoselektivitat.

Aryl and heteroaryl halides (X=Br, I) undergo a fast and convenient halogen-lanthanum exchange with nBu2 LaMe, which leads to functionalized diaryl- and diheteroaryllanthanum derivatives. Subsequent trapping reactions with selected electrophiles, such as ketones, aldehydes, or amides, proceeded smoothly at -50 °C in THF, affording polyfunctionalized alcohols and carbonyl derivatives. Kinetic competition experiments revealed a similar reactivity trend as for Br/Mg exchange, but 106 -times higher rates, making it comparable to Br/Li exchange.

An ambient temperature continuous flow method for nucleophilic amidation and thioamidation is described. Deprotonation of formamides by lithium diisopropylamine (LDA) affords carbamoyllithium intermediates that are quenched in situ with various electrophiles such as ketones, allyl bromides, Weinreb and morpholino amides. The nature of the reactive lithium intermediates and the thermodynamics of the metalation were further investigated by ab initio calculations and kinetic experiments.

The aromatic character of fused polycyclic systems varies with the nature of their annulated rings. Computed extra cyclic resonance energies (ECREs) reveal that the central six membered rings (6MRs) of the heterocyclic fused congeners 1-5 are "[6]radialene-like", but that the central 6MRs of triphenylene 9, coronene 10, and isocoronene 11 are "benzene-like." Comparisons with geometric (harmonic oscillator model of aromaticity, HOMA) and magnetic (nucleus independent chemical shifts, NICS) criteria illustrate the multifaceted nature of aromaticity in 1-11.

The kinetics of the reactions of carbocations with carbanions 1 derived from 5-benzyl-substituted Meldrum's acids 1-H (Meldrum's acid = 2,2-dimethyl-1,3-dioxane-4,6-dione) were investigated by UV/Vis spectroscopic methods. Benzhydryl cations Ar2CH(+) added exclusively to C-5 of the Meldrum's acid moiety. As the second-order rate constants (kC) of these reactions in DMSO followed the linear free-energy relationship lg k = sN (N+E), the nucleophile-specific reactivity parameters N and sN for the carbanions 1 could be determined. In contrast, trityl cations Ar3C(+) reacted differently. While tritylium ions of low electrophilicity (E-2) reacted with 1 through rate-determining β-hydride abstraction, more Lewis acidic tritylium ions initially reacted at the carbonyl oxygen of 1 to form trityl enolates, which subsequently reionized and eventually yielded triarylmethanes and 5-benzylidene Meldrum's acids by hydride transfer.

Zugabe von TMPLi zu Mischungen einer aromatischen oder heteroaromatischen Verbindung und eines Metallsalzes, beispielsweise MgCl2, ZnCl2 oder CuCN, bei −78 °C fuhrt zunachst zu einer Lithiierung des Arens gefolgt von einer Transmetallierung mit dem Metallsalz zu funktionalisierten Mg-, Zn- bzw. Cu-Organometallverbindungen. Diese In-situ-Abfangmethode ermoglicht die schnelle Metallierung einer Vielzahl an empfindlichen Pyridinen (mit Nitro-, Ester-, oder Cyangruppen) und gestattet die Herstellung kinetischer Regioisomere funktionalisierter Arene und Heterocyclen, die durch ubliche Metallierungsreagentien wie TMPMgCl⋅LiCl oder TMPZnCl⋅LiCl nicht zuganglich sind.

The addition of TMPLi to a mixture of an aromatic or heteroaromatic substrate with a metal salt such as MgCl2, ZnCl2, or CuCN at -78 °C first leads to lithiation of the arene followed by transmetalation with the metal salt to afford functionalized organometallic compounds of Mg, Zn, or Cu. This in situ trapping method allows an expedited metalation (-78 °C, 5 min) of a range of sensitive pyridines (bearing a nitro, ester, or cyano group) and allows the preparation of kinetic regioisomers of functionalized aromatic compounds or heterocycles not otherwise available by standard metalating agents, such as TMPMgCl⋅LiCl or TMPZnCl⋅LiCl.

The reactions of anilines (N-nucleophiles) and enamines (C-nucleophiles) with NO2 and SO2CF3 substituted aromatic triflones were investigated spectrophotometrically in acetonitrile at 20 °C. We found that the second-order rate constants k1 related to the C–N and C–C bond forming step of these nucleophilic aromatic substitution reactions (SNAr) and σ-complexation reactions follow the three-parameter equation log k(20 °C) = sN(N + E), allowing the determination of the electrophilicity E of such aromatic triflones for the first time. The ranking of these neutral electron-deficient compounds on the comprehensive electrophilicity scale defined by Mayr et al. reveals that the most electrophilic triflone, the 1,3,5-tris(trifluoromethanesulfonyl)benzene (TTSB), has an electrophilicity higher than that of the 1,3,5-trinitrobenzene (TNB) the common reference aromatic electrophile in anionic σ-complexation chemistry, by roughly 6 units of E. This finding holds promise for expanding the range of coupling reactions which can be envisioned between this series of electron-deficient neutral aromatics and nucleophiles.

Ein praktischer stereoselektiver Iod-Lithium-Austausch ermoglicht erstmals die Synthese von funktionalisierten stereodefinierten acyclischen sekundaren nicht-stabilisierten Lithiumreagentien aus den entsprechenden sekundaren Alkyliodiden. Diese Lithiumreagentien reagieren mit verschiedenen Elektrophilen, einschlieslich Kohlenstoff-Elektrophilen, unter hoher Retention der Konfiguration. Kinetische Daten zur konfigurationellen Stabilitat dieser acyclischen Alkyllithiumreagentien werden prasentiert. Die Methode bietet einen neuen, allgemeinen Zugang zu chiralen Synthons fur die stereoselektive Synthese von offenkettigen Molekulen.