Enantioselective sensing of amines based on [1 + 1]-, [2 + 2]-, and [1 + 2]-condensation with fluxional arylacetylene-derived dialdehydes

Four induced circular dichroism (ICD) probes exhibiting a stereodynamic arylacetylene framework and terminal aldehyde units have been prepared. The CD silent sensors generate a strong chiroptical response to substrate-controlled induction of axial chirality upon selective [1 + 1]-, [2 + 2]-, and [1 + 2]-condensation. The intense Cotton effects can be exploited for in situ ICD analysis of the absolute configuration and ee of a wide range of amines.     

Photoreactions between [60]fullerene and various aromatic tertiary amines

The photoreactions of [60]fullerene with aromatic tertiary amines such as N,N-dimethylaniline and N,N-dimethyl-1-naphthylamine gave two or three types of [60]fullerene adducts. The reaction efficiency in the series of p-substituted N,N-dimethylanilines remarkably increased with increasing electron-donating properties of aromatic tertiary amines employed.     

Tandem catalytic allylic amination and [2,3]-Stevens rearrangement of tertiary amines

We have developed a catalytic allylic amination involving tertiary aminoesters and allylcarbonates, which is the first example of the use of tertiary amines as intermolecular nucleophiles in metal-catalyzed allylic substitution chemistry. This process is employed in a tandem ammonium ylide generation/[2,3]-rearrangement reaction, which formally represents a palladium-catalyzed Stevens rearrangement. Low catalyst loadings and mild reaction conditions are compatible with an unprecedented substrate scope for the ammonium ylide functionality, and products are generated in high yields and diastereoselectivities. Mechanistic studies suggested the reversible formation of an ammonium intermediate.     

Triptycenediols by rhodium-catalyzed [2+2+2] cycloaddition

An efficient, modular synthesis of triptycene derivatives is presented, in which the triptycene ring system is constructed from readily available anthraquinone and alkyne starting materials. A rhodium-catalyzed alkyne cyclotrimerization reaction serves as the key step in this new method for the preparation of these useful unnatural products.     

Regioselective [2 + 2 + 2] cycloaddition of a nickel-benzyne complex with 1,3-diynes

[reaction: see text] Reactions of nickel(0)-benzyne complexes with a range of symmetrically substituted 1,3-diynes in the presence of triethylphosphine lead to the regioselective formation of 2,3-dialkynyl naphthalenes. The regioselectivity can be reversed when the diyne possesses substituents of high steric bulk, allowing selective formation of either symmetric dialkynyl naphthalene.     

Hydrogen reduction of the Cu(acac)2 complex sorbed by cucurbit[8]uril

The hydrogen reduction of bis(2,4-pentanedionato)copper(II) sorbed by the cavitand cucurbit[8]uril has been studied. After sorption of the complex at 180°C, the crystal structure of the resulting phase differs from the structure of the individual compounds. EPR shows that the reduction of the complex with hydrogen at 250°C for 15 min leads to the loss of one of the ligands and formation of the coordination bond between the Cu²⁺ ion and a nitrogen atom of cucurbit[8]uril and the oxygen atom of the water molecule or OH^? group located in the cavitand cavity. The molecular structure of the resulting supramolecular compound has been optimized by density functional theory quantum-chemical calculations with the exchange-correlation functional with the use of the PRIRODA program package. EPR, EXAFS, and XANES show that an increase in the reduction time or temperature (to 280°C) leads to the formation of copper clusters.     

Catalytic cycles for the reduction of [UO2]2+ by cytochrome c7 proteins proposed from DFT calculations

The mechanism of the reduction of the hydrated uranyl cation, [UO2](2+), by the cytochromes G. sulfurreducens and D. acetoxidans has been studied using density functional theory calculations. We propose that the initial electron transfer step from the heme is to a cation-cation complex in the case of D. acetoxidans, but for G. sulfurreducens, it is to a single uranyl cation, which then forms a U(V)-U(VI) complex with a second uranyl cation. For both enzymes, the subsequent catalytic pathways are very similar. A U(V)-U(V) complex is formed, which then undergoes disproportionation via two successive protonation steps of one uranyl group, to give a U(VI)-U(IV) complex which dissociates to individual U(VI) and U(IV) species, the former being bound at the enzyme active site. Intermediate structures along the catalytic pathway are consistent with EXAFS data.     

Thermal analysis of calix[4]resorcinarene complexes with secondary and tertiary amines

Tetra-n-undecylcalix[4]resorcinarene forms solid adducts with secondary and tertiary amines. Thermal decomposition of these complexes was investigated by means of thermogravimetry (TG) and differential scanning calorimetry (DSC). It was found that deamination of complexes occurs as multi-step process. The stoichiometry of complexes was evaluated on the basis of TG studies and total heats of deamination were calculated from DSC measurements.Presented at the CCTA9 31.08-05.09 2003, Zakopane PolandThis work was supported by Grant No. 3T09A 02419 from The Polish Committee for Scientific Research. The authors thank to prof. W. Zielenkiewicz for helpful discussion during realisation of this project and prof. T. Borowiak for X-ray structure of the tetra-n-undecylcalix[4]resorcinarene. tetra-n-undecylcalix[4]resorcinarene.     

Intramolecular ketenimine-ketenimine [2 + 2] and [4 + 2] cycloadditions

Bis(ketenimines), in which the two heterocumulenic functions are placed in close proximity on a carbon skeleton to allow their mutual interaction, show a rich and not easily predictable chemistry. Intramolecular [2 + 2] or [4 + 2] cycloadditions are, respectively, observed when both ketenimine functions are supported on either ortho-benzylic or 2,2'-biphenylenic scaffolds. In addition, nitrogen-to-carbon [1,3] and [1,5] shifts of arylmethyl groups in N-arylmethyl-C,C-diphenyl ketenimines are also disclosed.     

Nitrogen heteroaromatic cations by [2+2+2] cycloaddition

A modular approach to the construction of monocationic quaternary N-heteroaromatic frameworks was developed capitalizing on a direct pyridine-type nitrogen quaternization followed by metal-catalyzed [2+2+2] cycloaddition with gaseous acetylene. The flexibility of the route is demonstrated on 12 diverse scaffolds based on pyridinium, quinolinium, thiazolium, benzothiazolium, imidazolium, and pyrimidinium. Electrochemical study revealed a quinolinium redox system with two electrochemically distinct forms that are interconverted by a homogeneous chemical reaction triggered by fast electron transfers (reduction at -0.7 V and oxidation at -0.05 V).     

Unexpected reactions of [60]fullerene involving tertiary amines and insight into the reaction mechanisms

Thermal reactions of [60]fullerene with amino acid ester hydrochlorides and triethylamine in o-dichlorobenzene at reflux afforded pyrrolidinofullerene derivatives containing the CH(3)CH moiety and originating from triethylamine through an unusual C-N bond cleavage. Detailed investigation of these thermal reactions resulted in the discovery of unprecedented reactions between C(60) and tertiary amines and of reactions of C(60) with tertiary amines and aldehydes, giving cyclopentafullerene derivatives with high stereoselectivity. Plausible reaction mechanisms for the product formation involving the uncommon C-N bond cleavage of tertiary amines were proposed on the basis of extensive experimental results.     

Intramolecular formal [4+2] cycloaddition reactions of secondary and tertiary aryldiacetylene alcohols

Thermal and thionyl chloride induced cycloaromatizations of secondary and tertiary aryldiacetylene alcohols were studied. The secondary alcohol did not respond to thionyl chloride, but in all the other cases presumptive biradical intermediates evolved either by intramolecular radical coupling or, when derived from a xanthene scaffold, by intramolecular radical acylation to a diketone that finally afforded a p-methylene-quinone.     

NHC-catalyzed enantioselective [2 + 2] and [2 + 2 + 2] cycloadditions of ketenes with isothiocyanates

The enantioselective N-heterocyclic carbene-catalyzed formal [2 + 2] and [2 + 2 + 2] cycloaddition of ketenes and isothiocyanates were developed. Reaction with N-aryl isothiocyanates at room temperature favors the [2 + 2] cycloaddition, while reaction with N-benzoyl isothiocyanates at -40 °C favors the [2 + 2 + 2] cycloaddition.     

Electrochemical reduction of dibromodiketones facile [3+2] cycloaddition with olefins

Electrochemical reduction of 2,2-dibromo-1,3-diketones in the presence of olefins afforded the [3+2] cycloadducts, 2,3-dihydrofuran derivatives, regioselectively.     

DFT study on [4+2] and [2+2] cycloadditions to [60] fullerene

The functionalisation of C₆₀ fullerene with 2,3-dimethylene-1,4-dioxane (I) and 2,5-dioxabicyclo [4.2.0]octa-1(8),6-diene (II) was investigated by the use of density functional theory calculations in terms of its energetic, structural, field emission, and electronic properties. The functionalisation of C₆₀ with I was previously reported experimentally. The I and II molecules are preferentially attached to a C—C bond shared and located between two hexagons of C₆₀ via [4+2] and [2+2] cycloadditions bearing reaction energies of ?15.9 kcal mol^?1 and ?72.4 kcal mol^?1, respectively. The HOMO-LUMO energy gap and work function of C₆₀ are significantly reduced following completion of the reactions. The field electron emission current of the C₆₀ surface will increase after functionalisation of either the I or II molecule.