Cis Compounds Research Articles

Influence of the stereochemical configuration on the radical polymerization of methacrylic monomers:cis- andtrans-(2-cyclohexyl-1,3-dioxan-5-yl) methacrylate

The synthesis of two new isomeric monomers, cis-(2-cyclohexyl-1,3-dioxan-5-yl) methacrylate (CCDM) and trans-(2-cyclohexyl-1,3-dioxan-5-yl) methacrylate (TCDM), starting from the reaction of glycerol and cyclohexanecarbaldehyde, is reported. The process involved the preparation of different alcohol acetals and esterification with methacryloyl chloride of the corresponding cis and trans 5-hydroxy compounds of 2-cyclohexyl-1,3-dioxane. The radical polymerization reactions of both monomers, under the same conditions of temperature, solvent, monomer, and initiator concentrations, were studied to investigate the influence of the monomer configuration on the values of the propagation and termination rate constants (kp and kt ).The values of the ratio kp /kt 1/2 were determined by UV spectroscopy by the measurement of the changes of absorbance with time at several wavelengths in the range 275–285 nm, where an appropriate change in absorbance was observed. Reliable values of the kinetics constants were determined by UV spectroscopy, showing a very good reproducibility of the kinetic experiments. The values of kp /kt 1/2, in the temperature interval 45–65 °C, lay in the range 0.40–0.50 L1/2/mol1/2s1/2 and 0.20–0.30 L1/2/mol1/2s1/2 for CCDM and TCDM, respectively. Measurements of both the radical concentrations and the absolute rate constants kp and kt were also carried out with electron paramagnetic resonance techniques. The values of kp at 60 °C were nearly identical for both the trans and cis monomers, but the termination rate constant of the trans monomer was about three times that of the cis monomer at the same temperature. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3883–3891, 2000

Multinuclear NMR study and crystal structures of complexes of the types cis- and trans-Pt(Ypy) 2X 2, where Ypy=pyridine derivative and X=Cl and I

Complexes of the types cis- and trans-Pt(Ypy) 2X 2 where Ypy is a methyl derivative of pyridine and X=Cl or I were studied by spectroscopic methods, especially by multinuclear NMR spectroscopy. In 195Pt MNR, the cis-dichloro compounds were observed between −1998 and −2021 ppm in CDCl 3, while the trans compounds were found at slightly lower field, between −1948 and −1973 ppm. The diiodo species were observed at much higher field, between −3199 and −3288 ppm for the cis isomers and between −3122 and −3264 ppm for the trans isomers. In 1H NMR, the 3 J( 195Pt 1H) coupling constants are larger for the cis compounds (about 42 ppm) than for the trans isomers (about 33 ppm). In 13C NMR, the values of 3 J( 195Pt 13C) were also found to be larger for the cis complexes. There seems to be a slight dependence of the p K a values of the protonated ligands on the δ(Pt) chemical shifts. The presence of π-bonding between Pt and the pyridine ligands do not seem very important. The crystal structures of three dichloro and five diiodo complexes were determined, in an attempt to obtain information on the trans influence of the three ligands. The results have shown that the iodo ligand has the greatest trans influence. Chloro and pyridine ligands seem to have similar trans influence, although, the chloro ligand seems to have a slightly larger influence than pyridine derivatives. One structure, trans-Pt(2-pic) 2I 2, has shown a syn conformation of the two 2-picoline ligands.

Cellular pharmacology of cis and trans pairs of platinum complexes in cisplatin-sensitive and -resistant human ovarian carcinoma cells

The cellular pharmacology of two pairs of cis and trans platinum complexes has been studied in three human ovarian carcinoma cell lines, a parental relatively cisplatin-sensitive line (CH1), a subline possessing acquired cisplatin resistance (3-fold; CH1cisR) and an intrinsically cisplatin resistant line (13-fold; SKOV-3). Growth inhibition studies showed that both JM335 [ trans ammine (cyclohexylaminedichloro dihydroxo) platinum(IV)] and its platinum(II) dichloro homolog JM334 were relatively less cross-resistant against both acquired and intrinsic cisplatin resistant cells. In contrast, resistance circumvention was not apparent in these cell lines with their cis isomeric counterparts (JM149 for JM335 and JM118 for JM334). The trans compound JM335 was more potent than its cis isomer against all three cell lines. There was no clear correlation between intracellular accumulation following 2 h exposure to each compound and resulting DNA platination or growth inhibition. The selective activity of the trans platinum complexes against the SKOV-3 cell line correlated with a deficiency in the repair of adducts within a fragment of the N- ras gene induced by trans compounds whereas adducts induced by the cis counterparts, and cisplatin, were repaired. The CH1 parental line appeared repair deficient at the gene-specific level to adducts induced by both cis ( including cisplatin) and trans compounds. Resistance in CH1cisR was associated with a lack of gene-specific repair of lesions formed by JM118 and JM149. All four compounds induced apoptosis in all three cell lines, as measured by fluorescent microscopy and field inverted gel electrophoresis, although the kinetics of apoptosis was markedly faster for the trans versus cis compounds. In summary, the trans platinum complexes JM335 and JM334 possess unique cellular properties compared to their cis counterparts particularly with respect to gene specific repair of DNA adducts and the rate of induction of apoptosis.

Synthesis and pharmacology of site-specific cocaine abuse treatment agents: 2-(aminomethyl)-3-phenylbicyclo[2.2.2]- and -[2.2.1]alkane dopamine uptake inhibitors.

As part of a program to develop site-specific medications for cocaine abuse, a series of 2-(aminomethyl)-3-phenylbicyclo[2.2.2]- and -[2.2.1]alkane derivatives was synthesized and tested for inhibitory potency in [3H]WIN 35,428 binding and [3H]dopamine uptake assays using rat striatal tissue. Selected compounds were tested for their ability to substitute for cocaine in rat drug discrimination tests. Synthesis was accomplished by a series of Diels-Alder reactions, using cis- and trans-cinnamic acid derivatives (nitrile, acid, acid chloride) with cyclohexadiene and cyclopentadiene. Standard manipulations produced the aminomethyl side chain. Many of the compounds bound with high affinity (median IC50 = 223 nM) to the cocaine binding site as marked by [3H]WIN 35,428. Potency in the binding assay was strongly enhanced by chlorine atoms in the 3- and/or 4-position on the aromatic ring and was little affected by corresponding methoxy groups. In the [2.2.2] series there was little difference in potency between cis and trans compounds or between N, N-dimethylamines and primary amines. In the [2.2.1] series the trans exo compounds tended to be least potent against binding, whereas the cis exo compounds were the most potent (4-Cl cis exo: IC50 = 7.7 nM, 27-fold more potent than 4-Cl trans-exo). Although the potencies of the bicyclic derivatives in the binding and uptake assays were highly correlated, some of the compounds were 5-7-fold less potent at inhibiting [3H]dopamine uptake than [3H]WIN 35,428 binding (for comparison, cocaine has a lower discrimination ratio (DR) of 2.5). The DR values were higher for almost all primary amines and for the trans-[2.2.2] series as compared to the cis-[2.2.2]. Most of the compounds had Hill coefficients approaching unity, except for the [2. 2.2] 3,4-dichloro derivatives, which all had nH values of about 2.0. Two of the compounds were shown to fully substitute for cocaine in drug discrimination tests in rats, and one had a very long duration of action.

Bis(acetylacetonato)bis(cyclooctene)ruthenium(II), cis-[Ru(acac)2(η2-C8H14)2]: a synthetic precursor to trans- and cis-bis(acetylacetonato)ruthenium(II) complexes †

Reduction of [Ru(acac)3] with zinc amalgam or zinc dust in hot THF containing some water in the presence of an excess of cyclooctene generated in solution cis-[Ru(acac)2(η2-C8H14)2], which cannot be isolated in solid form but has been identified on the basis of its 1H NMR spectrum. It is a useful synthetic precursor because the co-ordinated olefins are easily displaced by many ligands. Treatment with pyridine, tert-butyl isocyanide, tertiary phosphines, phosphites and triphenylarsine (L) at room temperature gave red-brown complexes trans-[Ru(acac)2L2], which isomerise in solution to the more stable cis compounds on heating. In contrast, the similarly prepared trimethylamine complex, trans-[Ru(acac)2(NMe3)2], does not undergo trans to cis isomerisation. Reaction of cis-[Ru(acac)2(η2-C8H14)2] with acetonitrile or triphenylstibine (L′) gave monosubstitution products cis-[Ru(acac)2(η2-C8H14)L′], which react on heating with an excess of L′ to give cis-[Ru(acac)2L′2]. Treatment of cis-[Ru(acac)2(η2-C8H14)2] (1 mol) with Ph2PCH2PPh2 (dppm) (2 mol) at room temperature gave trans-[Ru(acac)2(η1-dppm)2], whereas the ligands Ph2P(CH2)mPPh2 (L–L, m = 2, dppe; m = 3, dppp) under the same conditions gave oligomers [{Ru(acac)2(L–L)}n], which probably contain mutually trans-phosphorus atoms. On heating all three compounds are converted into cis-[Ru(acac)2(L–L)]. Treatment of trans-[Ru(acac)2L2] (L = NMe3 or PPh3) with CO at room temperature and pressure gave trans-[Ru(acac)2(CO)L], which, in the case of L = PPh3, isomerises to the cis compound on heating; reaction of trans-[Ru(acac)2(AsPh3)2] with CO under the same conditions gave cis-[Ru(acac)2(CO)(AsPh3)] directly. The structures of trans-[Ru(acac)2(CNBut)2], trans-[Ru(acac)2(PMePh2)2], cis-[Ru(acac)2(CNBut)2] (in the form of a molecular adduct with [Ru(acac)3]), cis-[Ru(acac)2(PMePh2)2] and trans-[Ru(acac)2(η1-dppm)2] have been determined by X-ray crystallography, and trends in the metal–ligand distances are discussed. The formation of trans-[Ru(acac)2L2] from cis-[Ru(acac)2(η2-C8H14)2] may proceed via a square-pyramidal intermediate [Ru(acac)2L].

NMR and computational study on the anomeric effect incis/trans-3,4-dihydro-2-alkoxy-4-substituted-2H,5H-pyrano[3,2-c][1]benzopyran-5-one derivatives

The configuration and conformation of cis/trans-3,4-dihydro-2-alkoxy-4-(alkyl- or aryl-substituted)-2H,5H-pyrano[3,2-c][1]benzopyran-5-one derivatives were studied by combined NMR and computational analyses. The cis/trans configurational assignments of all diastereoisomers were achieved via 2D NOESY experiments. The conformational analysis of cis compounds, performed via NMR and computational studies, allowed the establishment of a preference for the conformer with both substituents in the pseudo-equatorial orientations. For trans derivatives only the molecular mechanics analysis produced meaningful results, suggesting a general prevalence for the conformer bearing the 2-alkoxy group in a pseudo-axial and the 4-substituent in a pseudo-equatorial orientation. © 1997 John Wiley & Sons, Ltd.

Study of the aqueous reactions of K[Pt(Ph 2SO)Cl 3] with nitrile ligands and crystal structures of N(C 4H 9) 4[Pt(Ph 2SO)Cl 3], N(C 2H 5) 4[Pt(Ph 2SO)Br 3] and cis-Pt(Ph 2SO)(C 3H 5CN)Cl 2

The aqeuous reactions of K[Pt(Ph 2So)Cl 1] with nitriles were studied in different conditions of pH, mainly by 195Pt and 1H NMR. At normal pH (≈ 2.4), the ligands RCN have produced the neutral complexes Pt(Ph 2SO)(RCN)Cl 2. For acetonitrile, only the cis isomer was obtained, while for other nitriles a mixture of the two isomers was formed. The 195Pt NMR spectra of the compounds were measured. The signals of the cis isomers were observed around −3040 ppm, while those of the trans isomers were found around − 3180 ppm. The study has shown that the first product formed is the trans isomer, which then isomerizes partially to the cis compounds. The 195Pt NMR spectra of the products obtained in neutral medium (pH adjusted to ∼ 7 with NaOH) have shown several signals depending on the nitrile. Dimeric species of the type Pt(Ph 2SO)Cl(μ-NHC(R)O 2Pt(Ph 2SO)Cl are suggested to exist in solution. Head-to-head and head-to-tail isomers are probably formed. The crystal structures of N(C 4H 9) 4[Pt(Ph 2SO)Cl 3] ( I), N(C 2H 5) 4[Pt(Ph 2SO)Br 3] ( II) and cis-Pt(Ph 2SO)(C 3H 5CN)Cl 2 ( III) were determined. The chloro ionic complex is triclinic, P-1, with a = 10.674(2), b = 11.424(2), c = 13.731(2) A ̊ , α = 89.54(1), β = 83.27(1), γ = 80.48(1)°, Z = 2 rmand R = 0.042, while the bromo complex is monoclinic, P2 1/ n, with a = 11.258(3), b = 19.425(4), c = 11.590(2) A ̊ , β = 102.62(2)°, Z = 4 and R = 0.053 . Crystal III is orthorhombic, space group P2 12 12 1, a = 9.532(3), b = 11.787(2), c = 15.464(4) A ̊ , Z = 4 and R = 0.031 . The compound is the cis isomer. For crystal I, the PtCl bond in trans position to the sulfoxide is 2.312(2) Å, while the cis bonds are 2.282(2) and 2.299(2) Å. For the bromo compound ( II), the PtBr bonds vary between 2.397(3) and 2.421(3) Å. In crystal III, the PtCl bond located in trans position to the nitrile is considerably shorter (2.269(3) Å) than the PtCl bond in trans position to the sulfoxide ligand (2.311(3) Å). The PtS bond distances vary between 2.201(2) and 2.228(3) Å.

Preparation of the stereoisomers of 2-cyanocycloalkanols by lipase-catalysed acylation

Enantiopure (1 R,2 R)-, (1 S,2 S)- and (1 R,2 S)-2-cyanocyclopentanol and -cyclohexanol isomers were prepared through the Pseudomonas cepacia lipase-catalysed acetylation of the racemic cis and trans compounds with vinyl acetate in diisopropyl ether. The quasi-irreversible nature of acylations with 2,2,2-trifluoroethyl esters is evident.

The vibrational spectra and ab initio calculations of trans- and cis-1,3-dibromo-1,3-dimethylcyclobutane

Infrared spectra of the title compounds were recorded as vapours, as solutes in various solvents, and as solids at ambient temperature and at 80 K. Raman spectra of the solids were obtained at various temperatures between ambient and 80 K. While trans-1,3-dibromo-1,3-dimethylcyclobutane exists in one puckered conformer only, the cis compound can be present as a mixture of diequatorial and diaxial bromine conformers. In the trans compound a large majority of the IR and Raman bands of the crystal did not coincide, suggesting C 2h molecular symmetry. Accordingly, this cyclobutane ring appears to be planar or very close to planar in the crystal, as observed for certain cyclobutanes. However, no significant changes between the IR spectra of the vapour, melt and crystal were detected. No additional IR or Raman bands of the cis compound were detected in the vapour phase, in the melt or in saturated solutions compared to the solid state spectra, suggesting the presence of negligible amounts of the diaxial bromine conformer. The IR and Raman spectra of the trans and cis compounds were assigned and compared with the results of ab initio quantum chemical calculations employing the basis sets STO-3G, HF/3-21G∗ and HF/6-31G∗.

Characterization of vinyl-substituted, carbon-carbon double bonds by GC/FT-IR analysis.

Vapor-phase infrared spectra allow the determination of the stereochemistry of carbon-carbon double bonds conjugated with a vinyl group. Cis and trans isomers of unsubstituted 1,3-alkadienes can be differentiated on the basis of the differences observed in the 900-1000 cm-1 region (spectra of cis isomers show two bands at 993 and 906 cm-1, while those of trans compounds show three absorptions at 998, 949, and 902 cm-1) and the 1590-1650 cm-1 region (the C=C stretch bands are observed at 1595 and 1642 cm-1 for cis compounds and at 1604 and 1650 cm-1 for trans compounds). Compounds bearing CH2=CHC(CH3)=CHCH2- and CH2=CHC(=CH2)-CH2- structural moieties, referred to as alpha- and beta-type compounds, are frequently encountered as natural products. For compounds bearing alpha-type groups, the cis/trans configuration of the trisubstituted double bond can be determined unambiguously. An absorption at 3095-3091 cm-1, for the =CH2 stretch vibration, is common to both of these groups; however, due to the presence of two =CH2 groups, the relative intensity of the band is much higher for beta-type compounds. For alpha-type compounds, a cis configuration at the C-3 carbon atom is characterized by a =CH2 wag absorption at 907-906 cm-1. For beta-type compounds and 3E-alpha-type compounds, this band appears at 899-897 cm-1. In addition, a wavy "fingerprint" pattern with two minima at 1632 (low intensity) and 1595-1594 cm-1 (high intensity) is characteristic for beta-type compounds. Our generalizations are based on spectra of cis and trans ocimene, myrcene, and dehydration products of many 3-methyl-1-alken-3-ols. Six isomers of farnesene can be characterized by GC/FT-IR. Furthermore, gas-phase IR allows the determination of the configuration of the trisubstituted double bond at C-3 in alpha-type farnesene congeners. For example, the homo- and bishomofarnesene isomers from Myrmica ants were shown to include a 3Z bond.

Lewis acid-catalyzed [4+2]type cycloadditions of aldimines bearing α-hydrogens with 2-silyloxy-1,3-butadienes

Abstract Trans-2,6-disubstituted-4-piperidones were synthesized by [4+2]type cycloaddition of chiral aldimines (5) with 2-silyloxy-1,3-butadiene (3) in the presence of Lewis acids. In the cycloaddition, only two 2,6-trans isomers (chelation and nonchelation products) were observed and no cis compounds were detected regardless of the Lewis acid used. Chelation-controlled products 6b, 8b, and 9b were obtained selectively by the use of TiCl4-i-PrCN and 6a was obtained with high selectivity when TMSOTf or Zn(OTf)2 was used as a Lewis acid at 4°C. The scope of the reaction is also described.

All‐TRANS, 13‐CIS and 9‐CIS retinoic acids induce a fully reversible growth inhibition in HNSCC cell lines: Implications for in vivo retinoic acid use

Retinoids are a group of vitamin A analogues that have shown promise as chemopreventive and therapeutic agents in many types of malignancy and have been entered in clinical trials with some successful results. To better understand the mechanism that mediates retinoid action and the anti-proliferative effects, we treated 7 human oral squamous-cell carcinoma (SCC) cell lines (FADU, HEp-2, CCL-17, SCC-9, SCC-15, SCC-25 and HN-212) with 10 6 M of all-trans retinoic acid (ATRA), 9-cis and 13-cis retinoic acid (RA) in continuous for different periods of time. We assessed the extent of growth inhibition, the stability of the anti-proliferative effect and the mRNA expression levels (by RT-PCR) of RA receptors (RARs), retinoid X receptors α (RXRα) and cytosolic RA-binding proteins (CRBP I and CRABP II) in treated cells compared with controls. The data obtained showed that all 3 RAs were able to inhibit the cellular growth of the tested cell lines, although to a different extent. The cis compounds were able to inhibit the proliferation of all cell lines, whereas ATRA was ineffective in inhibiting the proliferation of the CCL-17 cell line, which was naturally resistant to ATRA concentrations in the range between 10 5 and 10 6 M. All inhibitory effects were completely reversible since all cell lines restored their normal growth proliferation within few days after drug removal. RT-PCR analysis of the receptor and cell binding protein status of control and treated cells showed a good correlation between growth inhibition and induction of, or increase in, the expression levels of RARβ in RA-treated cells. No differences were observed in RARα and RXRα mRNA expression levels between control and treated cells. CRBP I, CRABP II and RARγ mRNA levels increased in some treated cell lines but not in all. Int. J. Cancer, 70:194–200, 1997. © 1997 Wiley-Liss, Inc.

Tetracyclic analogues of [+]-S 14297: Synthesis and determination of affinity and selectivity at cloned human dopamine D 3 vs D 2 receptors

Starting from the structure of the preferential D 3 antagonist S 14297 ( 1), we have prepared a series of cis and trans tetracyclic derivatives of general formula I in order to improve potency and selectivity for D 3 receptors. The trans oxazino derivative 2c, showed slightly increased affinity at D 3 receptors and double the selectivity for D 3 over D 2 receptors, in comparison to S 14297. Cis derivatives and compounds where R 1 is aralkyl were totally devoid of activity.

Fast-atom Bombardment (FAB) Mass Spectra of Nitrile or Cyanamide Complexes with the {M(Ph2PCH2CH2PPh2)2}n+ (M=Fe or Re) Metal Sites. Application to Reactions Induced under FAB Conditions

The fast-atom bombardment (FAB) mass spectra, in 3-nitrobenzyl alcohol (NOBA) matrices, of the cyanamide or organonitrile complexes trans-[FeH(NCR)(dppe)2][BF4] [1; R=NH2, NMe2, NEt2 or NC(NH2)2; dppe=Ph2PCH2CH2PPh2] and cis- or trans-[ReCl(NCR)(dppe)2] (2; R=aryl), which have a diphosphinic {M(dppe)2}n+ metal centre, are presented and discussed. Molecular ions have been detected for 1, [R=NH2 or NC(NH2)2], and only for the trans isomers of 2 in agreement with the higher stability of their oxidized forms in comparison with those of the cis compounds. Possible fragmentation patterns are proposed, involving the stepwise elimination of ligands from the metal (NCR, H and dppe for 1; Cl, NCR and dppe for 2), preceding (for 1) the fragmentation of the diphosphine ligand which, nevertheless, for complexes 2, can also occur in the presence of the chloride ligand. This is interpreted on the basis of the relative electron donor ability of the ligands. Different fragmentation modes are observed for the dppe ligand, involving, e.g., dehydrogenation and loss of C2H4, Ph·, PPh or P·, in processes involving reductive or oxidative elimination steps. Rhenium fragment ions are more susceptible to oxygenation than the iron ones, in accord with the greater tendency of the former metal to reach higher oxidation states. The identification of reactions induced and monitored by FAB-MS was also essayed and although trans-[FeHCl(dppe)2] (3) the starting material for the synthesis of complexes (1) and NCNMe2 do not react per se in solution, we have detected their reaction under FAB conditions, the spectra being interpreted by considering the addition of the substrate to fragment ions generated in situ from 3; a comparison with the solution chemistry is discussed and suggestions for its further development, towards lower metal oxidation state complexes, are presented on the basis of the FAB-MS reactions detected.

Synthesis and study of Pt(II)–nitrile complexes. Multinuclear NMR spectra and crystal structures of compounds of the types [Pt(R-CN)Cl3]− and cis and trans-Pt(R-CN)2Cl2

Complexes of the type [Pt(R-CN)Cl3]− were synthesized and studied by 1H, 13C, and 195Pt NMR spectroscopies. The 2J(195Pt-13C) coupling constants are about 240 Hz. The signals due to the cyano carbon atoms of the coordinated ligands were observed at higher fields than those of the free ligands. The shielding on the cyano carbon increases as the alkyl chain lengthens and also when the branching increases. The 195Pt signals of all the complexes were observed around −2000 ppm. The crystal structures of (NMe4)[Pt(C3H7-CN)Cl3] (1) and (NMe4)[Pt(p-HO-C6H4-CN)Cl3] (2) were determined. Compound 1 is monoclinic, P21/c, a = 8.384(5), b = 15.336(19), c = 11.759(9) Å, β = 99.52(6)°, Z = 4, R = 0.054, and wR = 0.051. Crystal 2 is tetragonal with a = 16.222(6), c = 12.052(5) Å, Z = 8, R = 0.059, and wR = 0.044. The Pt—CL bond trans to the nitrile ligand is shorter than normal (2.276(3) Å for 1 and 2.264(7) Å for 2) while the two other bonds are normal (2.293(4), 2.287(3) Å for 1 and 2.320(7), 2.275(8) Å for 2). The Pt—N bonds are 1.97(1) Å (1) and 1.92(2) Å (2) and the segments Pt-N≡C-C are linear. Disubstituted compounds were also synthesized and studied by multinuclear NMR. The 195Pt signals of the cis isomers were observed at lower fields than those of the trans isomers (Δ ≈ 65 ppm), while the 13C signals of the cyano carbons of the trans isomers were observed at lower fields than those of the cis compounds (Δ ≈ 0.6 ppm). The cis complexes isomerize to the trans compounds upon heating. The crystal structures of cis-(3) and trans-Pt(C2H5-CN)2Cl2 (4) and also of cis-Pt(p-HO-C6H4-CN)2Cl2 (5) were determined. Crystal 3 is monoclinic, P21/c, a = 7.506(5), b = 9.539(5), c = 14.823(7) Å, β = 92.31(4)°, Z = 4, R = 0.050, and wR = 0.042. The trans isomer 4 is monoclinic with the Pt atom on an inversion centre, P21/c, a = 5.149(4), b = 9.394(8), c = 10.944(10) Å, β = 97.84(7)°, Z = 4, R = 0.017 and wR = 0.020. Finally, compound 5 is triclinic, P-1, a = 7.464(3), b = 10.712(6), c = 12.291(5) Å, α = 75.63(4)°, β = 75.63(4)°, γ = 80.32(4)°, Z = 2, R = 0.045, and wR = 0.056. The Pt—Cl bond distances for the cis isomers are 2.269(5), 2.270(4) Å for 3 and 2.274(2), 2.279(3) Å for 5 while they are 2.289(3) Å for the trans isomer (4). The Pt—N bonds are 1.962(14), 1.988(11) Å (3), 1.972(7), 1.976(7) Å (5) and 1.969(5) Å for 4. Key words: platinum, nitrile, NMR, isomerization, crystal structure.

5467492 Dry-cleaning of garments using liquid carbon dioxide under agitation as cleaning medium

The polarographic behaviour of trans azodioxycyclohexane and trans α,α'-azodioxytoluene has been investigated in ethanol-water solutions.In acid medium, a preprotonation of the molecule and the cleavage of an oxygen are first observed, leading to the corresponding azoxy compound (2 electron step). A second reduction step leads to the hydrazo compound through the intermediate azo compound (4 electron step). In neutral medium, a single 6 electron reduction wave is observed.The neutral molecule is reduced in alkaline medium; an unstable intermediate is formed which dehydrates very fast into cis and trans azoxy compounds. In the case of trans α,α'-azodioxytoluene, both cis and trans azoxy compounds are reduced to α,α'-hydrazotoluene which is the final reduction product. In the case of trans azodioxycyclohexane, the corresponding trans azoxy compound is no longer reducible and a mixture of azo, hydrazo and trans azoxy compounds is obtained.

STEREOCHEMISTRY IN THE PROTONATION OF ENOLATES GENERATED FROM 2-SUBSTITUTED 2-CYCLOPENTEN-1-ONES BY THE 1, 4-ADDITION OF TRIALKYLSILYL AND TRIBUTYLSTANNYL ANIONS

Abstract The 1, 4-addition of trialkylsilyl anions to 2-(phenylseleno)-2-cyclopenten-1-one affords trans cyclopentanone derivatives. A similar trans selectivty was observed in the protonation of enolates derived from phenylseleno-or phenylthiocyclopentenones by the addition of the vinyl anion corresponding to the prostaglandin ω-chain. On the other hand, the 1, 4-additions of trialkylsilyl and tributylstannyl anions to 2-(2-propenyl)-2-cyclopenten-1-one lead to a predominant formation of the cis compounds.

Gas-Phase Infrared Spectroscopy for Determination of Double Bond Configuration of Monounsaturated Compounds

Gas-phase Fourier-transform infrared spectra allow unambiguous determination of the configuration of the double bonds of long-chain unsaturated compounds bearing RCH=CHR' type bonds. Although the infrared absorption at 970-967 cm-1 has been used previously for the identification of trans bonds, the absorption at 3028-3011 cm-1 is conventionally considered to be incapable of distinguishing cis and trans isomers. In this paper, we present a large number of gas-phase spectra of monounsaturated long-chain acetates which demonstrate that an absorption, highly characteristic for the cis configuration, occurs at 3013-3011 cm-1, while trans compounds fail to show any bands in this region. However, if a double bond is present at the C-2 or C-3 carbon atoms, this cis=CH stretch absorption shows a hypsochromic shift to 3029-3028 and 3018-3017 cm-1, respectively. Similarly, if a cis double bond is present at the penultimate carbon atom, this band appears at 3022-3021 cm-1. All the spectra of trans alkenyl acetates showed the expected C-H wag absorption at 968-964 cm-1. In addition, the spectra of (E)-2-alkenyl acetates show a unique three-peak "finger-print" pattern which allows the identification of the position and configuration of this bond. Furthermore, by synthesizing and obtaining spectra of appropriate deuteriated compounds, we have proved that the 3013-3011 cm-1 band is representative of the C-H stretching vibration of cis compounds of RCH=CHR' type.

Fluorinated pyrimidines. Part 4. Synthesis, properties and stereochemical conversion of the cis and trans isomers of 6-alkoxy-5-fluoro-5,6-dihydrouracils

The reaction of 6-acetoxy-5-fluoro-5,6-dihydrouracil with ROH (R = Me, Et, Pr, Pri, Bu, But) under acidic conditions has been investigated using 18F as a tracer. The quantitative replacement of the OAC-group proceeded predominantly with cisoid(gauche) stereochemistry, but upon prolonged heating the amount of the trans compound increased. This isomerization did not originate from epimerization at C5. The trans compounds—apart from being more stable towards substitution and elimination than the corresponding cis compounds—gave invariably substitution products with inversion of configuration, while the cis compounds mainly retained their configuration. Within the concept of the unifying ion-pair mechanism it is proposed that the trans compound reacts via an intimate protonated intermediate and the cis compound via a solvent-separated protonated intermediate. As a result, it was not the gauche attraction between the fluorine atom and the incoming nucleophile, but the poor π-donor ability of the C–F bond that was the determining factor in the cisoid stereochemistry of 5-fluoro-5,6-dihydrouracil adducts.

Gas phase infrared spectroscopy in characterization of unsaturated natural products

Abstract