Search

Five new tartrate-containing Keplerate compounds have been synthesized and characterized in the solid state and in solution. These characterizations evidenced the total replacement of inner sulfate ligands by L- or D-tartrate ligands in aqueous medium under heating during several days. To our knowledge these compounds correspond to the first Keplerate molecules incorporating chiral ligands. The H NMR studies supported by X-ray crystallographic analysis are consistent with the coordination of 24-30 tartrates within the Mo capsule which are located in close vicinity. The NMR signals of the encapsulated ligands appear particularly broad which precludes the use of advanced NMR methodologies but the solid state NMR provided further characterization of ligand substitution within the capsule by carboxylates. To our knowledge it is the first time that a solid state NMR study of a Keplerate is reported in the literature. [ABSTRACT FROM AUTHOR]

The cyclizations of enynes substituted at the alkyne gives products of formal [4+2] cyclization with Au(l) catalysts. 1,8-Dien-3-ynes cyclize by a 5-exo-dig pathway to form hydrindanes. 1,6-Enynes with an aryl ring at the alkyne give 2,3,9,9a-tetrahydro-1 H-cyclopenta[b]naphthalenes by a 5-exo-dig cyclization followed by a Friedel-Crafts-type ring expansion. A 6-endo-dig cyclization is also observed in some cases as a minor process, although in a few cases, this is the major cyclization pathway. In addition to cationic gold complexes bearing bulky biphenyl phosphines, a gold complex with tris(2,6-di-tert-butylphenyl)phosphite is exceptionally reactive as a catalyst for this reaction. This cyclization can also be carried out very efficiently with heating under microwave irradiation. DFT calculations support a stepwise mechanism for the cycloaddition by the initial formation of an anti-cyclopropyl gold(l)-carbene, followed by its opening to form a carbocation stabilized by π interaction with the aryl ring, which undergoes a Friedel-Crafts-type reaction. [ABSTRACT FROM AUTHOR]

This study addresses the challenges associated with vinyl cation generation, a process that traditionally requires quite specific counterions. Described herein is a novel intramolecular vinylation of arenes catalyzed by aluminum(III) chloride, utilizing practical conditions and readily available vinyl triflates derived from 2-aceto-3-arylpropionates. Comprehensive experimental data support diverse carbocycle synthesis, exemplified by indenes and higher analogues. Control experiments verify the applicability of the vinylation protocol, and synthetic applications showcase a potent tubulin polymerization inhibitor with anticancer properties. Density functional theory computations reveal a Lewis-acid-driven mechanism involving triflate moiety abstraction to generate a reactive vinyl cation.

Difluoromethylene-skipped enones have been readily obtained from arylvinyltriflates and aryldifluoroenoxysilanes. While these useful compounds are difficult to synthesize by the classical aldol/dehydration approach, the use of a squaramide/Li + catalyst allows their direct formation via a vinyl carbocation paired with a weakly coordinating perfluorinated alkoxyaluminate. This strategy makes possible a reaction between a typically weak electrophile and a weak nucleophile. Control experiments and DFT computations shed light on the mechanism of this transformation.

The concept of alkynophilicity is revisited with group 13 MX 3 metal salts (M = In, Ga, Al, B; X = Cl, OTf) using M06-2X/6-31+G(d,p) calculations. This study aims at answering why some of these salts show reactivity toward enynes that is similar to that observed with late-transition-metal complexes, notably Au(I) species, and why some of them are inactive. For this purpose, the mechanism of the skeletal reorganization of 1,6-enynes into 1-vinylcyclopentenes has been computed, including monomeric ("standard") and dimeric (superelectrophilic) activation. Those results are confronted with deactivation pathways based on the dissociation of the M-X bond. The role of the X ligand in the stabilization of the intermediate nonclassical carbocation is revealed, and the whole features required to make a good π-Lewis acid are discussed.

The catalytic activity of cationic NHC-Zn II and NHC-Al III (NHC=N-heterocyclic carbene) complexes in reactions that require the electrophilic activation of soft C-C π bonds has been studied. The former proved able to act as a soft π-Lewis acid in a variety of transformations. The benefit of the bulky IPr NHC ligand was demonstrated by comparison with simple ZnX 2 salts. The tested NHC-Al III catalyst is not able to activate C-C π bonds but simple AlX 2 + ions were found potent in some cases., (© 2020 Wiley-VCH GmbH.)

Herein, we report the preparation of bridged tetrahydrobenzo[b]azepines, which was accomplished through an aza-Piancatelli cyclization/Michael addition sequence in a one-pot fashion from readily available precursors. It is noteworthy that a general method to access these scaffolds was hitherto unprecedented. Additionally, the multifaceted aspects of this process have been exemplified through its application to the synthesis of 2-azabicyclo[3.2.1]octanes and bridged tetrahydrobenzo[b]oxepines, along with post-derivatizations., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A compound that isomerizes into distinct products depending on the particular Lewis acid or Brønsted acid catalyst used is disclosed. One product can only be obtained with the softest π-acids, such as Au, Pt, Ga, or In complexes. Another is formed only with harder π-acids incorporating Ag or Cu salts. The formation of the third category requires even harder π-acids or protons. This simple benchmark reaction allows for prediction of the category of transformations that can be catalyzed by a new complex. It also informs whether protons have been unintentionally generated in the reaction mixture., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An efficient synthesis of polysubstituted 2-alkenylfurans using Ca(NTf 2 ) 2 /KPF 6 as a catalytic mixture is described. It is based on the cycloelimination of readily available propargyl alcohols tethered to β-keto esters under dry conditions to avoid competitive Meyer-Schuster rearrangement. The furan can be further functionalized in situ by a calcium-catalyzed Friedel-Crafts-type reaction with secondary and tertiary alcohols. The title reaction allows for the high-yielding preparation of di-, tri-, and tetrasubstituted 2-alkenylfurans, which are important subunits of bioactive compounds., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

By reacting IPr⋅InBr3 with AgSbF6 in dichloroethane at room temperature, we could obtain single crystals comprising [{(IPr⋅InBr3 )(Ag⋅(CH2 Cl)2 )}2 ][SbF6 ]2 (1) and two identical HSbF6 units. It is presumed that the reaction gave rise to [IPr⋅InBr3-x ][SbF6 ]x (x=1, 2, or 3) which reacted with adventitious water to give HSbF6 and [IPr⋅InBr3-x (OH)][SbF6 ]x-1 . The experiment was reproduced at 60 °C, eventually leading to the indium hydroxide [{IPr⋅In(OH)0.5 (H2 O)4.5 }2 ][SbF6 ]5 (2)., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report a rare case of alkene transfer hydrogenation using a main-group compound instead of a transition-metal complex as catalyst. We disclosed that 1,4-cyclohexadiene can be used as H2 surrogate towards olefin reduction in the presence of [IPrGaCl2 ][SbF6 ]. Hydrogenative cyclizations have also been carried out because this cationic gallium complex is also a potent hydroarylation catalyst., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A molecular donor-acceptor adduct has been isolated by the reaction of the N-heterocyclic carbene 1,3-dimethyl imidazol-2-ylidene (diMe-IMD) with GaCl(3). In contrast, the structurally related, yet much more nucleophilic, 1,3-dimethyl-2-methylene-2,3-dihydro-1H-imidazole (diMe-MDI) gave rise to ion pairs of type [L(2)GaX(2)][GaX(4)], where X = Cl, Br, or I. With IBioxMe(4), a N-heterocyclic carbene that is more nucleophilic than diMe-IMD, the outcome of the reaction was dependent on the nature of the halide. Ionic 1:1 adducts between monodentate ligands and GaX(3) salts have only one precedent in the literature. The peculiar behavior of carbon-based ligands was explained on the basis of their electronic properties and reaction kinetics.

A new cyclization and C-H activation/Stille cross-coupling reaction on a nonactivated aromatic has been discovered. The reaction is regioselective and controlled by the stannylated reagent. Labeling experiments have been performed that provide evidence for a complete transfer of the deuterium through the coordination sphere of palladium. [reaction: see text]