Synthesis and reactions of a monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide

A 3-monosubstituted dithiirane 1-oxide, 3-(9-triptycyl)dithiirane 1-oxide, was prepared for the first time, by the reaction of (9-triptycyl)diazomethane and S₈O. The dithiirane 1-oxide was obtained as cis- and trans-isomers, and the structure of the trans-isomer was verified by X-ray crystallography. The cis-isomer isomerized gradually to the trans-isomer in solution. The divalent sulfur atom of the cis- and trans-dithiirane 1-oxides were removed on treatment with triphenylphosphine to give the corresponding Z- and E-sulfines, respectively. The reaction of the trans-dithiirane 1-oxide with (Ph₃P)₂Pt(C₂H₄) provided the (sulfenato-thiolato)Pt^II complex, and that with Lawesson's reagent yielded the 1,3,4,2-trithiaphospholane and 1,2,4,5,3-tetrathiaphosphorinane derivatives.     

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.     

Potential Stereoselective Binding of Trans-(±)-Kusunokinin and Cis-(±)-Kusunokinin Isomers to CSF1R

Breast cancer cell proliferation and migration are inhibited by naturally extracted trans-(−)-kusunokinin. However, three additional enantiomers of kusunokinin have yet to be investigated: trans-(+)-kusunokinin, cis-(−)-isomer and cis-(+)-isomer. According to the results of molecular docking studies of kusunokinin isomers on 60 breast cancer-related proteins, trans-(−)-kusunokinin was the most preferable and active component of the trans-racemic mixture. Trans-(−)-kusunokinin targeted proteins involved in cell growth and proliferation, whereas the cis-(+)-isomer targeted proteins involved in metastasis. Trans-(−)-kusunokinin targeted CSF1R specifically, whereas trans-(+)-kusunokinin and both cis-isomers may have bound AKR1B1. Interestingly, the compound’s stereoisomeric effect may influence protein selectivity. CSF1R preferred trans-(−)-kusunokinin over trans-(+)-kusunokinin because the binding pocket required a ligand planar arrangement to form a π-π interaction with a selective Trp550. Because of its large binding pocket, EGFR exhibited no stereoselectivity. MD simulation revealed that trans-(−)-kusunokinin, trans-(+)-kusunokinin and pexidartinib bound CSF1R differently. Pexidartinib had the highest binding affinity, followed by trans-(−)-kusunokinin and trans-(+)-kusunokinin, respectively. The trans-(−)-kusunokinin-CSF1R complex was found to be stable, whereas trans-(+)-kusunokinin was not. Trans-(±)-kusunokinin, a potential racemic compound, could be developed as a selective CSF1R inhibitor when combined.     

Solvent dependent photo-isomerization of 4-dimethylaminoazobenzene carboxylic acid

We have observed reversible trans–cis photo-isomerization behaviors of 4-dimethylaminoazobenzene carboxylic acid (4DAzC) in ethyl acetate by alternating irradiations at 370 and 430 nm. The photo-isomerization from trans- to cis-isomer was found to be strongly solvent dependent and not to occur efficiently in water and ethanol. Also photo-isomerization from cis- to trans-isomer was occurred upon 370 nm illumination or via thermal relaxation. The activation energy for the thermal isomerization from cis to trans-isomer was estimated to be 49.2 kJ/mol in ethyl acetate from the temperature-dependent kinetic absorption measurements.     

Synthesis and pharmacological activity of silyl isoxazolines 2

Silyl isoxazolines have been synthesized by [2+3] cycloaddition reaction of nitrile oxides to vinyl- and allylsilanes. The addition of 3-pyridylnitrile oxide to 1,3-divinyl-1,1,3,3-tetraphenyldisiloxane affords 1,3-bis{5-[3-(3-pyridyl)isoxazolin-2-yl]}-1,1,3,3-tetraphenyldisiloxane; the latter exists as a mixture of trans- and cis-isomers.The bond angle of the Si–O–Si fragment in thetrans-isomer equals 180(3)° and in the cis-isomer it is 162(3)°.The pharmacological properties of 4-[3-(5-trimethylsilylisoxazolin-2-yl)]pyridinium-chloride have been studied.     

Thermally-reversible photoisomerization of trans-dinitrobis(tri-N-propylphosphine)palladium(II)

UV irradiation of trans-dinitrobis(tri-n-propylphosphine)palladium(II) in MeOH yields a photostationary trans-cis mixture which reverts quantitatively in the dark to the trans-form. The cis-isomer, which can be isolated in crystalline form by irradiation of trans-species in n-hexane, has been characterized by UV, IR ¹H and ³¹P NMR spectroscopy. Irradiation of a 1/1 mixture of trans-[(PBu₃ⁿ)₂Pd(NO₂)₂] and trans-[(PPr₃ⁿ)₂Pd(NO₂)₂] gives almost entirely a 1/1 mixture of the corresponding cis-isomer, indicating an intramolecular process.     

Heterobimetallic [Ru(II)/Fe(II)] complexes: On the formation of trans- and cis-[RuCl2(dppf)(diimines)]

The synthesis and characterization of trans/cis-[RuCl₂(dppf)(diimines)], dppf = 1,1′-bis(diphenylphosphino)ferrocene; diimines = 2,2′-bipyridine (trans/cis-(1)), the new complexes with 4,4′-dimethyl-2,2′-bipyridine (trans/cis-(2)) and 1,10-phenanthroline (cis-(3)) are presented. The complexes were synthesized using two routes and the trans/cis-isomer formation is dependent upon conditions and the precursor applied. The trans-isomer (kinetic) readily isomerizes to the cis-isomer (thermodynamic) when exposed to light (fluorescent) and this process was followed by cyclic voltammetry and UV-vis. The electrochemical studies on these complexes reveal that Fe^(III)/Fe^(II) couples are insensitive to the isomer (trans/cis) formed, but the Ru^(III)/Ru^(II) couples are dependent on the isomer. Transfer-hydrogenation reactions for reduction of acetophenone were conducted using complexes cis-(1) and cis-(2) and the results are compared with that obtained for similar complexes. X-ray structure for cis-(3) are presented and discussed.     

Studies on the stereochemistry of 1,2,6-trimethyl-4-piperidone

In the effort to create new derivatives of analgesically active spiropiperidines intermediate 1,2,6-trimethyl-4-piperidone was synthesized. The substitution of the skeleton gives rise to configurational as well as conformational isomerism. Despite the symmetry of 1,2,6-trimethyl-4-piperidone two different sets of signals were present in the ¹H and ¹³C NMR spectra. They were supposed to arise from a cis/trans mixture of 1,2,6-trimethyl-4-piperidone. In contrast to this explanation only two signals of the methyl groups and hydrogens at carbon atoms 2 and 6 were observed in the ¹H and ¹³C NMR spectra, normally expecting one for the cis- and two for the trans-isomer. To solve this discrepancy, the kind of isomeric mixture of 1,2,6-trimethyl-4-piperidone leading to the ¹H and ¹³C NMR spectra was examined. Energy differences between chair conformations of both the cis- and the trans-isomer of 1,2,6-trimethyl-4-piperidone and the potential energy surface of the equilibration process of the trans-isomer of 1,2,6-trimethyl-4-piperidone between its chair conformers were determined by quantum chemical calculations. The barrier height of the equilibration process was measured by high and low temperature NMR measurements to confirm the theoretical outcome. The results of all investigations agree nicely and proved a cis-/trans-mixture of 1,2,6-trimethyl-4-piperidone being present at room temperature.     

CHARACTERIZATION OF CIS- AND TRANS-DINITROBIS-(l-CYCLOHEXANEDIAMINE)-COBALT(III) CHLORIDE1

Abstract

Two geometrical isomers of [Co(l-chxn)₂(No₂)₂]Cl have been isolated. The trans-isomer is eluted first from a cellulose ion exchange column as a single isomer. The cis-isomer corresponds to the complex previously reported as the trans-isomer. The cis-isomer with the same CD sign pattern as for the trans-isomer is stereoselectively favored, but a small amount of the second cis-isomer separates using Cellex CM ion exchange cellulose. The CD spectra of the cis- and trans- isomers are similar to those of the corresponding isomers of the l-pn complex.     

trans-chloro(N,N-dimethyl-d-phenylglycine)-(3-methyl-1-phenylpent-1-ene)platinum(II) complexes. HPLC separation and identification of all the diastereomers

The diastereomeric trans-chloro(N,N-dimethyl-d-phenylglycine)(3-methyl-1-phenylpent-1-ene)platinum(II) complexes, derived by coordination of the enantiomeric and geometric isomers of 3-methyl-1-phenylpent-1-ene (2), were separated by HPLC. Four trans- and two cis-olefin complexes were recognized in the chromatogram. The configuration of all chiral centers of the olefin in the six complexes were assigned. Under the conditions of preparation, the pairs of diastereomers 1R,2R,3S/1S,2S,3S and 1S,2S,3R/1R,2R,3R were formed in a ratio > 1 for the trans-isomer, whereas the cis-isomer gave the 1R,2S,3S and 1S,2R,3R epimers only. The complexes do not epimerize on standing at room temperature in solution; similar behaviour of the corresponding complexes of trans-stilbene (4C) indicates that the conjugated aromatic double bond is coordinated more strongly than those aliphatic and cycloaliphatic olefins.The efficient HPLC separation of the diasteromeric complexes 2C, permits the enantiomeric analysis of 2, as well as the preparative resolution of the olefin.     

Analysis of methods for calculating the transition frequencies of the torsional vibration of acrolein isomers in the ground (S 0) electronic state

B3LYP, MP2, CCSD(T), and MP4/MP2 in the 6-311G(d, p), 6-311++G(d, p), cc-pVTZ, aug-cc-pVTZ bases used to calculate the transition frequencies of torsional vibration of trans- and cis-isomers of acrolein in the ground electronic state (S ₀) are analyzed. It is found that for trans-isomers, all methods of calculation except for B3LYP in the cc-pVTZ basis yield good agreement between the calculated and experimental values. It is noted that for the cis-isomer of acrolein, no method of calculation confirms the experimental value of the frequency of torsional vibration (138 cm^?1). It is shown that the calculated and experimental values for obertones at 273.0 cm^?1 and other transitions of torsional vibration are different for this isomer in particular. However, it is established that in some calculation methods (B3LYP, MP2), the frequency of the torsional vibration of the cis-isomer coincides with another experimental value of this frequency (166.5 cm^?1). It is concluded that in analyzing the vibrational structure of the UV spectrum, the calculated and experimental values of its obertone (331.3 cm^?1) coincide, along with its frequency. It is also noted that the frequency of torsional vibration for the cis-isomer (166.5 cm^?1) can also be found in other experimental works if we change the allocation of torsional transition 18 ₁ ¹ .     

Metals in organic syntheses: XIV. NMR,IR, and reactivity studies on the olefin hydroformylation catalyzed by Pt-Sn complexes

Among the several hydrides formed when trans-[PtHClL₂] (L = PPh₃) reacts with Sncl₂, only trans-[PtH(SnCl₃)L₂] rapidly inserts ethylene, at −80°C, to yield cis-[PtEt(SnCl₃)L₂]. At −10°C, cis-[PtEt(SnCl₃)L₂] irreversibly rearranges to the trans-isomer, thus indicating that the cis-isomer is the kinetically controlled species, and that the trans-isomer is thermodynamically more stable.At −50°C, a mixture of trans-[PtHClL₂] and trans[PtH(SnCl₃)L₂] reacts with ethylene to give cis-[PtEtClL₂] and cis-[PtEt(SnCl3)L₂] and this has been attributed to the catalytic activity of SnCl₂ which dissociates from cis-[PtEt(SnCl₃)L₂] at this temperature.Carbon monoxide promotes the cis-trans isomerization of cis[PtEt(SnCl₃)L₂], which occurs rapidly even at −80°C. This rearrangement is followed by a slower reaction leading to the cationic complex trans-[PtEt(CO)L₂]⁺ SnCl₃⁻. At −80°C, this complex does not react further, but when it is kept at room temperature ethyl migration to coordinated carbon monoxide takes place, to give several Pt-acyl complexes, i.e. trans-[PtCl(COEt)L₂], trans-[Pt(SnCl₃)(COEt)L₂], trans-[PtCl(COEt)l₂ · SnCl₂], and trans-[Pt(COEt)(CO)L₂]⁺ SnCl₃⁻. This mixture of Pt-acyl complexes reacts with molecular hydrogen to yield n-propanal and the same complex mixture of platinum hydrides as is obtained by treating trans-[PtHClL₂] with SnCl₂.Trans-[PtH(SnCl₃)L₂] reacts with carbon monoxide to yield the five-coordinate complex [PtH(SnCl₃)(CO)₂L₂], which has been characterized by NMR and Ir spectroscopy; ethylene does not insert into the PtH bond of this complex at low temperature. At room temperature, trans-[PtH(SnCl₃)L₂] reacts with a mixture of CO and ethylene to yield the same mixture of Pt-acyl species as is obtained when trans-[PtEt(SnCl₃)L₂] is allowed to react with CO.The role of a PtSn bond in these reactions is discussed in relation to the catalytic cycle for the hydroformylation of olefins.     

The X-ray structural characterization and solution dynamics of bis[(μ-2,6-dimethylphenylisocyanide)- (cyclopentadienyl)(2,6-dimethylphenylisocyanide)iron(I)]

The X-ray structure of trans-[{Fe(η⁵-C₅H₅)(CNC₆H₃Me₂-2,6)₂}₂] (1a) and the solution dynamics of both cis- and trans-[{Fe(η⁵-C₅H₅)(CNC₆H₃Me₂-2,6)₂}₂] have been studied. The trans-isomer of 1a crystallizes in the space group P2₁/n with a 14.588(4), b 8.811(2) and c 14.847(4) Å, β 92.08(2)°. The molecule lies across a crystallographic centre of inversion with a trans arrangement of cyclopentadienyl ligands and a strictly planar bridging Fe₂C₂ ring. The FeFe bond lenght is 2.518(1) Å and the bridging isocyanide ligands are symmetrically bonded to iron with a mean FeC(bridging) bond lenght of 1.928(3) Å. Solution ¹H NMR spectra of 1a show the presence of both cis- and trans-isomers, and a 500 MHz ¹H NMR study at low temperature reveals two distinct exchange processes; the lower energy one results in the coalescence of the signals for the inequivalent methyl groups on the bridging isocyanide ligands of the cis-isomer, whereas the higher energy process brings about coalescence of the methyl signals for the bridging and terminal isocyanide ligands of the trans-isomer. At elevated temperatures all the methyl signals coalesce.     

Die stereoisomeren bicyclo[4.2.0]octan-cis-Diole-(7,8)

The stereochemical assignment of the bicyclo[4.2.0]octane-cis-7,8-diols is reinvestigated. It is shown that the cis-diols prepared by different routes are indeed stereoisomers, the lower melting being the exo-isomer (1), the higher melting the endo-isomer (2). The synthesis of the previously unknown trans-fused bicyclo[4.2.0]octane-cis-7,8-diol (3) via photosensitized cycloaddition of vinylene carbonate to cyclohexene is described.     

Alkyl- und arylkomplexe des iridiums und rhodiums : VIII. Ungewöhnlich hoher trans-einfluss des carbonylliganden. Molekülstrukturen von cis- und trans-Ir(2,4,6-Me3C6H2)(CO)(PPh3)2

The molecular structures of cis- and trans-Ir(2,4,6-Me₃C₆H₂)(CO)(PPh₃)₂ have been determined by X-ray diffraction methods. Crystals of cis-Ir-(2,4,6-Me₃C₆H₂)(CO)(PPh₃)₂ (A) are monoclinic (P2₁/c) with a 1311.0(3), b 1888.5(6), c 1589.7(5) pm, β 101.85(2)°, and Z = 4. The trans complex B likewise crystallizes in the monoclinic space group P2₁/c with four molecules per unit cell, the lattice parameters being a 981.2(4), b 1214.7(7), c 3579.8(17) pm, and β 102.29(3)°. Based on 2971 and 2883 intensity data, the structures have been refined by full-matrix least squares to R values of 0.051 and 0.059 for A and B, respectively. The molecular geometries may be described as square planar. In the case of the cis-isomer the coordination shows some degree of tetrahedral distortion as a result of steric crowding. IrP distances in B are 231.3(5) and 231.9(5) pm, while in A IrP trans to mesityl is 232.4(3) pm, but trans to CO 237.0(3) pm. The carbonyl ligand thus seems to exert an even stronger trans-influence on IrP than the aryl group. This effect is discussed in terms of dπdπ participation in the metal—phosphine linkage. A very close contact of 244 pm is observed between the central metal and one of the ortho-methyl hydrogens in A which may contribute to kinetic stabilization of the thermodynamically unfavoured cis-isomer.     

Hydroisomerization of <Emphasis Type="Italic">cis</Emphasis>-Stilbene into <Emphasis Type="Italic">trans</Emphasis>-Stilbene on Supported Heterogeneous Metal Catalysts (Rh,Pd, Pt,Ru, Ir/α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>)

The hydroisomerization of a cis-isomer to produce a trans-isomer on Rh, Pd, Pt, Ru, and Ir/α-Al₂O₃ catalysts is studied. It is shown that Rh and Ru catalysts on which the hydroisomerization reaction mostly takes place exhibit the most favorable characteristics, whereas on the other metals, the main route is the hydrogenation reaction. Rh/α-Al₂O₃ is the optimum catalyst, since it has much higher activity than Ru/α-Al₂O₃. It is found that the increased selectivity of the trans-isomer formation is facilitated by a decrease in the hydrogen pressure and by an increase in the substrate concentration. The maximum selectivity is achieved when the reaction is carried out in nonpolar n-hexane and toluene, whereas in the case of the more polar tetrahydrofuran (THF), dimethylformamide (DMFA), and methanol both the reaction rate and the selectivity of the trans-isomer formation decline.     

Self-aggregation of synthetic zinc 31-hydroxy-131-oxo-17,18-cis-chlorin in a non-polar organic solvent

Zinc methyl 3¹-demethyl-17,18-cis-bacteriopheophorbide-d was prepared as a model of naturally occurring bacteriochlorophyll-d. From the absorption spectral analysis, the synthetic cis-chlorin self-aggregated in a non-polar organic solvent to give an oligomer possessing red-shifted and broadened peaks, compared to the non-aggregated form. The red-shifted values by self-aggregation were smaller than those observed in the corresponding trans-isomer, indicating that self-aggregates of the cis-isomer took on more disordered supramolecular structures than those of the trans-isomer.     

Synthesis of eleven-membered carbocycles via a homo-Cope type of five-carbon ring expansion reaction utilized β-(hydroxymethyl)allylsilane

Eleven-membered carbocycles were synthesized from six-membered compounds fitted with a β-(hydroxymethyl)allylsilane unit via the title reaction. Namely, trans- and cis-(E)-2-(trimethylsilylmethyl)-3-(2-vinylcyclohex-1-yl)prop-2-en-1-ol were treated with Tf₂O in CH₂Cl₂ in the presence of 2,6-lutidine to afford (1E)-3-methylenecycloundeca-1,6-diene in good yield. The geometry of the product was shown to depend upon the trans- and cis-substitution pattern on the cyclohexane ring of the substrates; i.e. trans-isomer afforded (6E)-product exclusively and cis-isomer afforded the mixture of (6E)- and (6Z)-product in 1:2 ratio. The (Z)-substrate with respect to allylsilane moiety afforded the same ring expansion product, however, the yield was lower than the reaction with the (E)-substrate. The substrates bearing t-butyl or benzyloxy substituents on the cyclohexane ring also afforded the product analogously, indicating that the reaction depends upon the conformation of the substrate. On the other hand, the substrate bearing isopropenyl group instead of a simple vinyl group did not afford the ring expansion product but produced bicyclo[5.4.0]undecane via the ene reaction.     

A systematic density functional and wavefunction-based study on dicarboxyl dianions −O2C–R–CO2 − with R = C2, C2X2, C2X4, and C6X4 (X = H, F)

The possible existence of the gas phase cis- and trans-maleate, i.e. completely deprotonated maleic acid (O₂C–CΗ=CΗ–CO₂)^2–, is investigated by density functional (B3LYP) and ab-initio quantum chemical methods (MP2, CCSD(T)) using large basis sets. The calculations reveal that only the trans-isomer is Coulomb stable with respect to electron loss. The results are compared to other previously investigated dicarboxylate dianions of the general form ^?O₂C–R–CO₂ ^? with R = C₂, C₂X₂, C₂X₄, and C₆X₄ (X = H, F). Fluorine substitution on the carbon framework helps to stabilize these doubly charged systems, and we predict that all of the aromatic fluorine substituted dicarboxylate dianions are Coulomb stable in the gas phase. Only the highest levels of theory reveal the slight stabilization of both the succinate dianion and the ortho-isomer of the phthalic acid dianion in unprecedented agreement with experiments.     

SmI2-induced cyclization of optically active (E)- and (Z)-β-alkoxyvinyl sulfoxides with aldehydes

SmI₂-induced reaction of (E)-β-alkoxyvinyl (R)- and (S)-sulfoxides with aldehydes effected a highly stereoselective intramolecular cyclization to give 2,6-anti-2,3-cis- and 2,6-syn-2,3-trans-tetrahydropyran-3-ols, respectively. The reaction of (Z)-(R)-isomer gave 2,6-syn-2,3-cis-tetrahydropyran-3-ol and a ring-opened product, and that of (Z)-(S)-isomer yielded many products.