Electrochemical studies and photoconversion of cis-and trans-6,6′-diethoxythioindigo

The reduction of cis- and trans-6,6′-diethoxythioindigo (DETI) at a platinum electrode in N,N-dimethylformamide (DMF) solution was studied by cyclic voltammetry and controlled potential coulometry. The cis-form, produced by photoisomerization of the trans-form, is reduced at less negative potentials than the trans-. The trans-isomer produces a fairly stable radical anion upon one-electron reduction; the cis-radical anion isomerizes rapidly to the trans-form and also dimerizes much more rapidly than the trans-isomer. A photogalvanic cell based on this system was devised but showed low efficiency for conversion of radiant energy to electricity.     

Synthesis and structure of some cis-and trans-myrtanylstannanes

Enantiomerically pure cis- and trans-myrtanylstannanes cis-MyrSnPh₃ (1), trans-MyrSnPh₃ (2), cis-MyrSnPh₂Cl (3), trans-MyrSnPh₂Cl (4), cis-MyrSnPhCl₂ (5), trans-MyrSnPhCl₂ (6), cis-MyrSnCl₃ (7), trans-MyrSnCl₃ (8) were synthesized and fully characterized by ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopy. The molecular structures of 1, 3, 6, 7, and [trans-MyrSn(OH)Cl₂ · H₂O]₂ (8a) a hydrolysis product of 8, were determined by X-ray crystallography.     

Stereoselective synthesis of cis- and trans-3-fluoro-1-phenylcyclobutyl amine

A stereoselective approach to the synthesis of cis- and trans-3-fluoro-1-phenylcyclobutylamine has been developed. Excellent stereoselectivity was obtained by the reduction of the appropriately substituted cyclobutanone to give either cis- or trans-isomers of 3-hydroxyl-1-phenylcyclobutylamine, which was stereoselectively converted to the 3-fluoro derivative.     

New stereoselective syntheses of cis- and trans-2-methyl-4-arylpiperidines

A stereoselective approach has been developed for the synthesis of cis- and trans-2-methyl-4-arylpiperidines from a common intermediate. The Ni-catalyzed hydrogenolysis of N-Boc-2-methyl-4-aryl-4-piperidinols, obtained by addition of organometallic reagents on N-Boc-2-methyl-4-piperidone, afforded the trans derivatives with up to 95% selectivity whereas the corresponding cis isomers were obtained in the presence of palladium catalysts.     

Facile stereoselective synthesis of cis- and trans-3-alkoxyazetidin-2-ones

A highly stereoselective synthesis of cis- and trans-3-alkoxy-3-phenyl/benzylthioazetidin-2-ones is described. The reaction of α-chlorosulfide-β-lactams with various alcohols catalyzed by a Lewis acid such as ZnCl₂ in the presence of molecular sieves (3-4 Å) leads to cis-3-alkoxy-3-phenyl/benzylthio-β-lactams whereas treatment of potassium 2-alkoxy-2-phenylthioethanoate with appropriate Schiff's base using POCl₃ in the presence of triethylamine leads to the formation of trans-3-alkoxy-3-phenylthioazetidin-2-ones as major products.     

Reactions of thebaine with cis- and trans-disubstituted dienophiles

Thebaine has been shown to undergo Diels-Alder reactions with trans-disubstituted ethylenes containing relatively bulky groups. These were correlated with reactions in which the corresponding cis-disubstituted dienophiles were used. Reductions, Grignard reactions and base-catalyzed rearrangements of the adducts are described.     

Baylis-Hillman chemistry: synthesis of cis- and trans-α-methylene-γ-lactones

syn-Homoallylic alcohols prepared from Baylis-Hillman adducts react with CBr₄/PPh₃ to give trans-α-methylene-γ-lactones. Notably, the same alcohols yield the cis-α-methylene-γ-lactones in the presence of traces of p-toluenesulfonic acid.     

Thermal and photochemical decomposition of cis- and trans-3,5-diphenyl-1-pyrazoline

The decomposition mechanism of the title compounds 8c and 8t is discussed. Dibenzylic 1,3-biradicals are suggested as intermediates.     

Synthesis of trans-4-aryl-3-(3-chloropropyl)azetidin-2-ones and their transformation into trans- and cis-2-arylpiperidine-3-carboxylates

Treatment of arylmethylideneamines with 5-chloropentanoyl chloride in benzene in the presence of 2,6-lutidine afforded novel trans-4-aryl-3-(3-chloropropyl)azetidin-2-ones in good yields. The latter 3-(3-chloropropyl)-β-lactams were transformed selectively into trans-methyl 1-alkyl-2-arylpiperidine-3-carboxylates in high yields and purity upon subsequent treatment with hydrogen chloride in methanol and triethylamine in dichloromethane. These trans-1-alkyl-2-arylpiperidine-3-carboxylates were easily converted into either their cis-isomers upon treatment with hydrazine monohydrate in methanol, or into the corresponding piperidine-1,3-dicarboxylates by reaction with alkyl chloroformates in benzene. Finally, 3-(3-chloropropyl)-1-(4-methoxybenzyl)-4-phenylazetidin-2-one was transformed into the corresponding trans-1-tert-butoxycarbonyl-3-(4-methoxybenzylcarbamoyl)piperidine via a three-step sequence in a good overall yield.     

Reductive ring opening of cis- and trans-2,3-diphenyloxirane: a common intermediate

The reaction of both cis- and trans-2,3-diphenyloxirane (7 and 4, respectively) with an excess of lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 2.5 mol%) in the presence of different carbonyl compounds as electrophiles (Barbier conditions) in THF at temperatures ranging between −80 and −50 °C gives the same organolithium intermediate 5 and consequently, the same 1,3-diols 6. In the case of cis-epoxide an inversion of the configuration at the benzylic carbanionic center can explain the obtained results. Only for the dicyclopropyl ketone derivative (6h) some amount (14%) of the corresponding epimer (6′h) resulting from a process with retention of the configuration of the intermediate is obtained. In representative cases, the structure of the final products (6) was unequivocally determined by X-ray diffraction analysis.     

Laser photolysis study of trans→cis photoisomerization of trans-1-phenyl-2-(2-naphthyl) ethylene

The direct trans→cis photoisomerization of trans-1-phenyl-2-(2-naphthyl) ethylene (trans-PNE) in liquid solution at room temperature was studied by the nanosecond laser photolysis technique. The time-resolved S_n←S₁ and T_n←T₁ absorption spectra were observed with trans-PNE at 300 K and 77 K. The lifetime of the triplet state of trans-PNE was found to be much shorter in liquid solution at room temperature than in rigid solution at 77 K. This fact and the effect of a triplet quencher shows that the photoisomerization of trans-PNE occurs mainly via the triplet state.     

Characterization of the photoisomers from cis- and trans-chlordanes, trans-nonachlor and heptachlor epoxide

Irradiation of acetone solutions of trans-chlordane (4a) and trans-nonachlor (4b) with UV light produces new half-cage photoisomers (5a or 6a and 5b or 6b, respectively) with bridging that differs from that of the photoisomers (2 and 8a) obtained from cis-chlordane (1b) and heptachlor epoxide (7). A new photoisomer (10) obtained from heptachlor epoxide is transformed into photoisomer 8a on further irradiation. Detailed PMR and ¹³C-NMR studies establish the structures of the new photoisomers and permit a decision between alternative formulations for the structures of the half-cage photoisomers of heptachlor epoxide and cis-chlordane,     

Synthesis of trans-vaccenic acid and cis-9-trans-11-conjugated linoleic acid

The preparation of the monounsaturated fatty acid, trans-vaccenic acid 4 (TVA), using both Wittig and one-pot Julia-Kocieński olefination protocol, was achieved in good yield. Similarly a Wittig approach was employed for the stereoselective synthesis of cis-9-trans-11-conjugated linoleic acid 2 from trans-2-nonenal and (8-carboxyoctyl)triphenylphosphonium bromide 12.     

A new and efficient catalytic isomerization of cis- and trans-epoxides

We report new ruthenium-catalyzed cis-trans isomerization of various functionalized epoxides. Enantiospecific isomerization of chiral epoxides is achieved without loss of enantiopurity, and epimerization occurs only at the epoxide carbon of the activating group.     

Regioselective cleavage of cis- and trans-2-methyl-3,4-epoxy alcohols with diethylpropynyl aluminum

The regioselectivity of the reaction of diethylpropynyl aluminum with diastereomeric 2-methyl-3,4-epoxy alcohols was studied. The preferred side of attack (1,3-diol vs 1,4-diol product) depends on the stereochemical disposition of the substituents. NMR studies showed that the regiochemistry of this reaction is governed by the aluminum coordination pattern. Protection of the alcohol with MEM provides the 1,3-diol product in systems where the free alcohol produced the 1,4-diols.     

The vibrational analysis and torsional study of trans-1,2-dimethylcyclopropane and cis-1,2-dimethylcyclopropane

The infrared spectra of cis-1,2-dimethylcyclopropane and trans-1,2-dimethylcyclopropane have been recorded between 4000 and 200 cm^?1 in the polycrystalline solid phase, and 4000 to 80 cm^?1 in the gas phase. The Raman spectra of these two compounds in the gaseous and liquid phases were also recorded between 3100 and 10 cm^?1. An assignment of the thirty-nine fundamental vibrations for both cis- and trans-1,2-dimethylcyclopropane is proposed, and comparisons are made with the vibrations of other similar molecules. Additionally, ten torsional transitions were observed in the far infrared and Raman spectra of cis-1,2-dimethylcyclopropane, and four transitions were observed in the spectra of the trans compound. From these spectral data, torsional barriers were determined. The effective barriers to methyl torsion are 2.92 kcal mol^?1 (12.20 kJ mol^?1) for cis-1,2-dimethylcyclopropane and 2.61 kcal mol^?1 (11.14 kJ mol^?1) for trans-1,2-dimethylcyclopronane.     

Light induced magnetic properties of spiropyrane tris(oxalato)chromate (III) single crystals

The effect of UV light on Weiss temperature and ESR spectra in 1-isopropyl-3, 3, 5′, 6′-tetramethylspiro[indolin-2,2′-[2H]pyrano[3,2-b]pyridinium] tris(oxalato)chromate (III) (Sp₃Cr(C₂O₄)₃) has been found. Additional line has been observed in the ESR spectra of irradiated samples in “strong” magnetic fields of ~15 kOe. The analysis of angular dependences of the ESR spectra allowed a contribution of Cr³⁺ ions to magnetic properties of Sp₃Cr(C₂O₄)₃ to be determined. The zero-field splitting parameters D=0.619 cm⁻¹, E=0.024 cm⁻¹ were derived from the experimental data. The parameters were typical for Cr³⁺ in the chromium oxalate. Weiss temperature changed sign from 25 to −25 K under UV irradiation. The value of Weiss temperature and its changing cannot be explained by exchange interaction, dipole-dipole interaction or the effect of crystal field. The existence of Weiss temperature is explained by the changes in amount and spin of paramagnetic particles. The change is due to thermoactivated redistribution of electrons between chromium ions and spiropyrane molecules. Light-induced transfer of electrons is also explaining the change in sign of Weiss temperature under UV irradiation.     

Ultrasound-accelerated aromatisation of trans- and cis-pyrazolines under heterogeneous conditions using claycop

A simple, efficient and eco-friendly procedure has been developed for the aromatisation of various pyrazolines in heterogeneous media using clay-supported copper(II) nitrate (claycop) under ultrasound activation. The reaction rate enhancement and the sonication effect are discussed.     

Enantioselective synthesis of cis-α-substituted cycloalkanols and trans-cycloalkyl amines thereof

The diastereo- and enantioselective syntheses of trans-cycloalkyl amines was accomplished through a three-step sequence consisting of: (1) asymmetric transfer hydrogenation through dynamic kinetic resolution of bicyclic and monocyclic α-substituted ketones using HCO₂H/Et₃N as the hydrogen source and TsDPEN-based Ru(II) catalysts, (2) nucleophilic hydroxyl to azide substitution of the resulting cis-cycloalkanols using diphenyl phosphoryl azide under modified Mitsunobu conditions, and (3) reduction of the trans-azide intermediates with LiAlH₄ of PPh₃/H₂O to the desired targets.