Mendel Fleisher

Trimethylsilylcyanation of aromatic aldehydes catalyzed by Pybox-AlCl3 complex

Abstract A series of aromatic and heterocyclic cyanohydrins and their O-silyl ethers have been synthesized by trimethylsilylcyanation of aldehydes using a catalyst generated in situ from ( S , S )-2,6-bis(4′-isopropyloxazolin-2′-yl)pyridine (Pybox) with AlCl 3 . Mandelonitrile was prepared in isolated yield 92% with more than 90% ee. The structure of AlCl 3 -Pybox complex was studied by means of 1 H NMR and quantum-chemical calculations.

Fluorescent substituted amidines of benzanthrone: synthesis, spectroscopy and quantum chemical calculations.

Several new substituted amidine derivatives of benzanthrone were synthesized by a condensation reaction from 3-aminobenzo[de]anthracen-7-one and appropriate aromatic and aliphatic amides. The obtained derivatives have a bright yellow or orange fluorescence in organic solvents and in solid state. The novel benzanthrone derivatives were characterized by TLC analysis, (1)H NMR, IR, MS, UV/vis, and fluorescence spectroscopy. The solvent effect on photophysical behaviors of these dyes was investigated, and the results showed that the Stokes shift increased, whereas quantum yield decreased with the growth of the solvent polarity. The structure of some dyes was confirmed by the X-ray single crystal structure analysis. AM1, ZINDO/S and ab initio calculations using Gaussian software were carried out to estimate the electron system of structures. The calculations show planar configurations for the aromatic core of these compounds and two possible orientations of amidine substituents. The calculation results correlate well with red-shifted absorption and emission spectra of compounds.

Halogenation of terminal acetylenes by perhalogenoalkanes under phase transfer catalysis conditions

Abstract Halogenation of terminal acetylenes by perhalogenoalkanes such as CCl4, CBr4 and CI4 under phase transfer catalysis conditions was studied. The influence of base and halogenating agent amounts on process of phenylacetylene bromination and iodination was discussed. The quantum chemical calculations of bromination of 2-pyridylacetylene using the semiempirical AM1 method were carried out.

Fluoride ion catalyzed silylation of ketoximes by hydrosilanes

Silylation of aromatic and heteroaromatic oximes with hydrosilanes in the presence of system CsF/18-crown-6/benzene was studied. Silyl ethers were isolated in yields up to 78%. Mechanism of fluoride ion catalyzed silylation of oximes was proposed on the basis of quantum chemical calculations using the semi-empirical AM1 method.

Novel fluoride ion mediated synthesis of unsymmetrical siloxanes under phase transfer catalysis conditions

Abstract Unsymmetrical siloxanes have been prepared from silanols or hydrosilanes using phase transfer catalytic (PTC) systems Me 3 SiN 3 –CsF–18-crown-6–toluene or Me 3 SiN 3 –CsF–18-crown-6–H 2 O–toluene, correspondingly. The target unsymmetrical siloxanes were prepared in yields up to 100%. Quantum chemical calculation of mechanism of unsymmetrical siloxanes formation has been performed.

Fluoride ion mediated reactions of disubstituted acetylenes Me3SiCCMMe3 (M=C, Si, Ge, Sn) with terminal acetylenes

Abstract The CsF–18-crown-6 mediated reactions of disubstituted acetylenes Me 3 SiCCMMe 3 (M=C, Si, Ge, Sn) with phenylacetylene and 2-methyl-5-pyridylacetylene in benzene have been studied. The first step of the reaction is the deprotonation of aryl acetylene by F − -ion. The carbanion formed interacts with the disubstituted acetylene. The silylated, germylated and stannylated acetylenes were formed in yields 26–91%. Quantum chemical calculations of trimethylsilyl and trimethylgermyl group transfer have been performed.

Synthesis and 1H, 13C, 14N, 15N, 29Si NMR study of trimethylsilylquinolines and their methiodides

Abstract 2-, 3-, 4-, 5-, 6-, 7- and 8-trimethylsilylquinolines and their methiodides as well as some 2-silyl-alkylquinolines were obtained by lithium synthesis in order to elucidate intramolecular donor-acceptor interactions between nitrogen and silicon atoms. 1 H, 13 C, 14 N, 15 N and 29 Si NMR spectra of the compounds were studied and quantum-chemical calculation of charges on individual atoms in the unsubstituted quinoline and in trimethylsilylquinoline molecule was carried out. The two-centered component of the total system energy for various bonds was calculated. The findings suggest donor-acceptor interaction between nitrogen and silicon atoms in 2-trimethylsilylquinoline that reduces electron density at nitrogen atoms. An apparently weaker interactions is observed in 8-trimethylsilylquinoline.

Novel amidine derivatives of benzanthrone: Effect of bromine atom on the spectral parameters

Several new substituted amidine derivatives of benzanthrone were synthesized by condensation reaction from 2-bromo-3-aminobenzo[de]anthracen-7-one and appropriate aromatic or aliphatic amides. The novel benzanthrone derivatives were characterized by TLC analysis, NMR, IR, MS, UV/Vis, and fluorescence spectroscopy. The obtained derivatives have yellow or orange fluorescence in organic solvents. The solvent effect on photophysical behaviors of these dyes was investigated, and the results showed that the introduction of a bromine atom causes a blue-shift of the absorption and emission bands and decrease in the fluorescent quantum yield in comparison with unbromated analogues. The difference in the excited state and the ground state dipole moments was estimated by using the variation of Stokes shift and by semiempirical molecular calculations. The crystal structure and packing of four novel dyes has been revealed by the X-ray single crystal structure analysis.

Study of the structure of (carbamimidoylsulfanyl)acetic (“pseudothiohydantoic”) acid by XRD and PM6 methods

It was shown by the method of powder X-ray diffraction analysis that in the crystalline state the product of the reaction of thiourea with chloroacetic acid in water, (carbamimidoylsulfanyl)acetic acid, existed in the zwitter-ion tautomeric form. The structure consists of virtually planar infi nite layers normal to the c axis of the unit cell which are bound by van der Waals interactions. The layers are formed by infi nite rows elongated along the b axis of the unit cell consisting of materially planar zwitter-ionic molecules linked by strong bifurcated hydrogen bonds. The results of quantum-chemical calculations by PM6 method are in agreement with the XRD results: whereas an isolated molecule exists in nonzwitter-ionic tautomeric form, in the crystal only the zwitterionic tautomer is present.

Crystal structure of 4-[2-(2-chlorophenyl)vinyl]-6,6-dimethyl- 2-oxo-1,2,5,6-tetrahydropyridine-3-carbonitrile, C16H15ClN2O

C16H15ClN2O, triclinic, P1 (no. 2), a =7 .6036(4) A, b =1 0.1520(7) A, c =1 0.4790(8) A, * =1 02.272(3)°, ) =1 08.689(3)°, ’ =9 6.463(3)°, V =7 34.4 A 3 , Z =2 , Rgt(F) =0 .060, wRref(F 2 ) =0 .176, T =2 93 K. Source of material Th es ynthesis of th et itl ec ompoun dw as performed by condensation of 4,6,6-trimethyl-2-oxo-1,2,5,6-tetrahydropyridine-3carbonyl with 2-chlorobenzaldehyde in ethanol solution in presence of catalyti ca mount of NaOH [1]. Single crystals of the compound were obtained by slow crystallization from ethanol solution at room temperature.