Use of X-ray diffraction data in stereochemical studies of (−)-menthone reactions with aromatic aldehydes

X-ray diffraction analysis proved that the stereochemical configuration of interaction products of (−)-menthone with aromatic aldehydes (α,β-unsaturated ketones or β-hydroxyketones) depends on the generation conditions of intermediate enolate carbanions. In irreversible deprotonation of (−)-menthone with strong sterically hindered organometallic bases, products of interaction with aldehydes preserve the 1R,4S-configuration; in equilibrium conditions, 1R,4R-diastereomers of the corresponding α,β-unsaturated ketones are formed with high stereoselectivity. Institute of Single Crystals, Academy of Sciences of Ukrainian Republic. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 5, pp. 133–142, September–October, 1994. Translated by T. Yudanova     

Dipyrazolinyl-substituted 1,4-distyrylbenzenes

A number of dipyrazolinyl-substituted 1,4-distyryl- and 1,4-distyryl-2-methylbenzenes — new luminophores that have intense yellow-green luminescence — were obtained by the Wittig reaction by refluxing 1-(4-formylphenyl)-3-aryl-5-phenyl-2-pyrazolines and aromatic bisphosphonium salts in isopropyl alcohol in the presence of sodium isopropoxide. The low reactivities of the aldehydes used and the predominant formation of trans isomers in the Wittig reaction are noted. Data from the IR and electronic absorption spectra and the fluorescence spectra of the synthesized compounds are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 532–535, April, 1979.     

X-Ray Investigation of Chiral β-Hydroxyketone Derived From (+)-Isomenthone

X-ray analysis was carried out to study the molecular structure of β-hydroxyketone, which is one of the minor products of selective aldol condensation of (−)-menthone with 4-carbomethoxybenzaldehyde. The cyclohexanone ring of the compound has a practically undistorted chair conformation with an axial orientation of the 1-methyl group and the bulkiest 2-[1′-hydroxy-1′ -(4-carbomethoxyphenyl)]methyl substituent and the equatorial orientation of the isopropyl group in the 4 position. The stereochemical configuration was found to be (1R,2R,4 R, 1′ S), supporting that the compound belongs to the group of (+)-isomenthones; i.e., the starting (-)-menthone undergoes (to a certain extent) epimerization under the reaction conditions used. In crystal, there is intermolecular hydrogen bonding >C=O...HO- (the -O...H- bond length is 2.15 Å). The molecular conformation in hydroxyketone crystals differs from the one which prevails in solutions (according to previous NMR data) and which is characterized by an inverted cyclohexanone ring and intramolecular hydrogen bonding >C=O...HO.Original Russian Text Copyright © 2004 by S. V. Shishkina, T. G. Drushlyak, L. A. Kutulya, N. S. Pivnenko, and O. V. Shishkin__________Translated from Zhurnal Strukturnoi Khimii, Vol. 45, No. 5, pp. 933–940, September–October, 2004.     

New (1R,4R)-2-arylidene-p-menthan-3-ones with a bridging ester group in the arylidene fragment. Synthesis and behavior in liquid-crystalline systems

(1R,4R)-2-(4-Hydroxybenzylidene)- and (1R,4R)-2-(4"-hydroxybiphenyl-4-yl)methylene-p-menthan-3-ones were synthesized by condensation of (–)-menthone with O-tetrahydropyran-2-yl derivatives of 4-hydroxybenzaldehyde and 4"-hydroxy-4-formylbiphenyl, respectively, in a DMSO—base medium followed by the removal of the protective group. The reactions of these hydroxy derivatives with 4-alkylbenzoic, 4-alkyloxybenzoic, trans-4-alkylcyclohexane-4-carboxylic, and 4"-alkylbiphenyl-4-carboxylic acids afforded three series of new chiral esters. Compounds containing the arylidene moiety with three benzene rings were found to exhibit liquid-crystalline properties. The characteristic features of these compounds are discussed based on the results of studies by polarizing microscopy, differential scanning calorimetry, and small-angle X-ray scattering. It was found that the mesomorphic compounds under study can form a smectic A mesophase, twist grain boundary mesophases (TGBA), and blue phases in a wide temperature range. Upon dissolution of certain of chiral compounds in 4"-cyano-4-pentylbiphenyl, a rather high twisting power and the thermal stabilizing effect on mesophases were observed.     

Synthesis and spectral-luminescence properties of 1-(4′-formylphenyl)-3,5-diaryl-2-pyrazolines

It was demonstrated by means of the IR and PMR spectra that 1-phenyl-3,5-diaryl-2-pyrazolines that contain a grouping with a strong electron-acceptor effect, viz. a 4-nitrophenyl or 4-naphthalanhydride group or a 1,8-naphthoylene-1,2-benzimidazole fragment, in the 3 position undergo Vilsmeier formylation, like unsubstituted 1,3,5-triphenyl-2-pyrazoline, in the para position of the 1-phenyl ring. An investigation of the spectral-luminescence properties of the synthesized 1-(4-formylphenyl)-3,5-diaryl-2-pyrazolines showed that the introduction in the 1-phenyl ring of an electron-acceptor aldehyde group, which is inferior with respect to its acceptor effect to the groupings in the 3 position of the heteroring, does not change the nature of the long-wave absorption band. Substantial hypsochromic and hypsofluoric effects as compared with the corresponding 1-phenyl-unsubstituted compounds are noted in the electronic spectra of these compounds.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 807–811, June, 1982.The authors thank I. D. Kalikhman for recording the PMR spectra.     

Proton Magnetic Resonance and Molecular Simulation in Configurational and Conformational Analysis of Cyclohexanone Derivatives

Developing the previously tested approach to the configurational and conformational analysis of cyclic chiral compounds based on a complex use of NMR spectra and molecular simulation, we determined the configuration 1R, 2R, 4R, 1S and conformational state of 2[1hydroxy1(4carbomethoxyphenyl) methyl]pmenthane3one, a minor product of the directed aldol reaction of (–)menthone with 4carbomethoxybenzaldehyde. The configurations of the cyclic chiral centers were determined by analysis of the spin–spin coupling constants of the protons of the cyclohexanone ring for the most probable conformations of alternative stereoisomers. The S configuration of the C (1) exocyclic chiral center was established from the different orientation of the benzene ring relative to the cyclohexanone fragment in alternative stereoisomers, as shown by semiempirical quantumchemical simulations (AM1 and PM3 methods), and from the observed difference in proton chemical shift between the examined hydroxyketone and the model (+)isomenthone (1R, 4Rdiastereomer).     

Molecular and crystal structures of 4′-hydroxy derivative of (3<Emphasis Type="Italic">R</Emphasis>,6<Emphasis Type="Italic">R</Emphasis>)-3-methyl-6-isopropyl-2-(4-phenylbenzylidene)cyclohexanone

The molecular and crystal structures of the 4-hydroxy derivative of (3R,6R)-3-methyl-6-isopropyl-2-(4-phenylbenzylidene)cyclohexanone are determined by X-ray diffraction analysis. Single crystals are orthorhombic, a = 9.147(2) Å, b = 12.959(2) Å, c = 15.695(5) Å, V = 1860.4(7) ų, Z = 4, and space group P2₁2₁2₁. The cyclohexanone ring in the crystal structure has an asymmetric chair conformation. The puckering parameters are as follows: the puckering amplitude S is 0.91, and the puckering angles θ and ψ are equal to 20.2° and 10.4°, respectively. It is established that the enone fragment and the cyclohexanone ring in molecules are flattened considerably. In the crystal structure, the molecules are linked by the

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hydrogen bonds (bond length, 1.85 Å). The structural features and the strength of the hydrogen bonds for the compound under investigation and its analogue with one benzene ring are compared using the X-ray diffraction and IR spectroscopic data.

     

New chiral imines based on S-α-phenylethylamine and S-α-benzylethylamine in induced cholesteric and smectic mesophases: II. Behavior of chiral dopants in ester liquid-crystal systems

The temperature dependences of the pitch of induced helical structures in the ester liquid-crystal systems containing hydroxyphenyl benzoate derivatives and chiral N-aroyloxybenzylidene-S-α-phenylethylamines or N-aroyloxybenzylidene-S-α-benzylethylamines have been measured. The twisting power of chiral dopants is calculated and the temperature dependence of the helical pitch in the induced cholesteric (N ^*) and smectic C ^* mesophases is quantitatively characterized. The parameters A = dT _is/dC that characterize the effect of dopants on the thermal stability of the N ^* phases are determined from the concentration dependences of the cholesteric-isotropic transition temperature T _ts for the n-hexyloxyphenyl-n-butylbenzoate-chiral dopant systems. The results obtained are compared with the data for the 4-n-pentyl-4′-cyanobiphenyl (5CB)-based cholesteric systems induced by the chiral dopants under consideration.     

Conformational analysis and steric effects of substituents in derivatives of 3-oxo-, 3-imino-, and 3-methylenecyclohexene

The equilibrium conformations and the inversion barriers of the rings in 3-oxo-, 3-imino-, 3-methylenecyclohexenes and in their methyl,tert-butyl, and phenyl derivatives were calculated by molecular mechanics. The unsubstituted molecules adopt a sofa conformation. The nonbonded interactions between substituents at positions 2 and 4 and the exocyclic double bond lead to a change in the conformation of the ring to a half-chair. The effect is enhanced as the volume of the substituent increases in the series of the oxo, imino, and methylene derivatives. Substituents at other positions of the ring affect only slightly the equilibrium conformation. The results of calculations were confirmed by X-ray structural analysis of 2-(4-benzoyloxybenzyl)-6-isopropyl-3-methylcyclohex-2-enone. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1995–2000, November, 1997.     

Basicity and structure of α,Β-unsaturated heterocyclic ketones

The constants of the protolytic equilibrium and the displacement of the frequency of the stretching vibrations of the hydroxy group of phenol taking place under the influence of the formation of a hydrogen bond with the compounds studied have been measured for dibenzylideneacetone and dibenzylidenecycloalkanones (with five-, six-, and seven-membered rings) and their furan and selenophene analogs. It has been shown that the screening of the carbonyl group of the aliphatic ring creates considerable steric hindrance for the solvation of the carbenium ions formed in an acid medium, as the result of which the constants of the protolytic equilibrium fall on passing from compounds with an open chain to the cycloalkanone derivatives. The inclusion of a carbonyl group in a five-membered aliphatic ring creates more favorable conditions for conjugation than exist in analogous compounds with an open chain and in those with six- and seven-membered rings, in consequence of which the capacity for forming a hydrogen bond changes in the corresponding sequence.For preceding communication, see [1].