Showing papers on "Double bond published in 2004"
TL;DR: In this paper, a review of the recent advances in the asymmetric hydrosilylation of ketones and imines is presented, which leads to very effective and selective protocols for the reduction of prochiral ketones, imines and electrophilic double bonds.
Abstract: This literature review focuses on the recent advances in the asymmetric hydrosilylation of ketones and imines. New catalyst systems based on various transition metals, such as rhodium, titanium, zinc, copper and tin, combined with classical or new ligand structures, are presented. These systems lead to very effective and selective protocols for the reduction of prochiral ketones, imines and electrophilic double bonds.
234 citations
TL;DR: In this article, the authors describe a coupling reaction of vinyl halides with amides or carbamates, which proceeds well at room temperature to 80 °C in dioxane to give enamides using N,N-dimethylglycine as the promoter and Cs2CO3 as the base.
199 citations
TL;DR: In this paper, the short-range structures of fluorine-graphite intercalation compounds with stage-1 structures, C x F ( x ǫ = 2.47, 2.84, 3.61), were analyzed by means of neutron diffraction.
198 citations
TL;DR: The synthesis and heterogenization of new Grubbs-Hoveyda type metathesis catalysts by chlorine exchange is described, and 3 was found to be highly active in RCM at room temperature (20 degrees C), allowing TONs up to 1400.
Abstract: The synthesis and heterogenization of new Grubbs-Hoveyda type metathesis catalysts by chlorine exchange is described. Substitution of one or two chlorine ligands with trifluoroacetate and trifluoromethanesulfonate was accomplished by reaction of [RuCl(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (IMesH(2) = 1,3-bis(2,4,6-trimethylphenyl)-4,5-dihydroimidazol-2-ylidene) with the silver salts CF(3)COOAg and CF(3)SO(3)Ag, respectively. The resulting compounds, [Ru(CF(3)SO(3))(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (1), [RuCl(CF(3)SO(3))([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (2), and [Ru(CF(3)CO(2))(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (3) were found to be highly active catalysts for ring-closing metathesis (RCM) at elevated temperature (45 degrees C), exceeding known ruthenium-based catalysts in catalytic activity. Turn-over numbers (TONs) up to 1800 were achieved in RCM. Excellent yields were also achieved in enyne metathesis and ring-opening cross metathesis using norborn-5-ene and 7-oxanorborn-5-ene-derivatives. Even more important, 3 was found to be highly active in RCM at room temperature (20 degrees C), allowing TONs up to 1400. Heterogeneous catalysts were synthesized by immobilizing [RuCl(2)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] on a perfluoroglutaric acid derivatized polystyrene-divinylbenzene (PS-DVB) support (silver form). The resulting supported catalyst [RuCl(polymer-CH(2)-O- CO-CF(2)-CF(2)-CF(2)-COO)([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (5) showed significantly reduced activities in RCM (TONs = 380) compared with the heterogeneous analogue of 3. The immobilized catalyst, [Ru(polymer-CH(2)-O-CO-CF(2)-CF(2)-CF(2)-COO)(CF(3)CO(2))([double bond]CH-o-iPr-O-C(6)H(4))(IMesH(2))] (4) was obtained by substitution of both Cl ligands of the parent Grubbs-Hoveyda catalyst by addition of CF(3)COOAg to 5. Compound 4 can be prepared in high loadings (160 mg catalyst g(-1) PS-DVB) and possesses excellent activity in RCM with TONs up to 1100 in stirred-batch RCM experiments. Leaching of ruthenium into the reaction mixture was unprecedentedly low, resulting in a ruthenium content <70 ppb (ng g(-1)) in the final RCM-derived products.
165 citations
TL;DR: In this article, the formation of the cyclic carbon trioxide isomer, CO3(X 1A1), in carbon-dioxide-rich extraterrestrial ices and in the atmospheres of Earth and Mars were investigated experimentally and theoretically.
Abstract: The formation of the cyclic carbon trioxide isomer, CO3(X 1A1), in carbon-dioxide-rich extraterrestrial ices and in the atmospheres of Earth and Mars were investigated experimentally and theoretically. Carbon dioxide ices were deposited at 10 K onto a silver (111) single crystal and irradiated with 5 keV electrons. Upon completion of the electron bombardment, the samples were kept at 10 K and were then annealed to 293 K to release the reactants and newly formed molecules into the gas phase. The experiment was monitored via a Fourier transform infrared spectrometer in absorption-reflection-absorption (solid state) and through a quadruple mass spectrometer (gas phase) on-line and in situ. Our investigations indicate that the interaction of an electron with a carbon dioxide molecule is dictated by a carbon–oxygen bond cleavage to form electronically excited (1D) and/or ground state (3P) oxygen atoms plus a carbon monoxide molecule. About 2% of the oxygen atoms react with carbon dioxide molecules to form the C2v symmetric, cyclic CO3 structure via addition to the carbon–oxygen double bond of the carbon dioxide species; neither the Cs nor the D3h symmetric isomers of carbon trioxide were detected. Since the addition of O(1D) involves a barrier of a 4–8 kJ mol−1 and the reaction of O(3P) with carbon dioxide to form the carbon trioxide molecule via triplet-singlet intersystem crossing is endoergic by 2 kJ mol−1, the oxygen reactant(s) must have excess kinetic energy (suprathermal oxygen atoms which are not in thermal equilibrium with the surrounding 10 K matrix). A second reaction pathway of the oxygen atoms involves the formation of ozone via molecular oxygen. After the irradiation, the carbon dioxide matrix still stores ground state oxygen atoms; these species diffuse even at 10 K and form additional ozone molecules. Summarized, our investigations show that the cyclic carbon trioxide isomer, CO3(X 1A1), can be formed in low temperature carbon dioxide matrix via addition of suprathermal oxygen atoms to carbon dioxide. In the solid state, CO3(X 1A1) is being stabilized by phonon interactions. In the gas phase, however, the initially formed C2v structure is rovibrationally excited and can ring-open to the D3h isomer which in turn rearranges back to the C2v structure and then loses an oxygen atom to ‘recycle’ carbon dioxide. This process might be of fundamental importance to account for an 18O enrichment in carbon dioxide in the atmospheres of Earth and Mars.
160 citations
TL;DR: In this paper, a series of salicylideneaniline (SA) derivatives 1 and 2 were prepared to study the substituent effect on the chromic properties.
Abstract: A series of salicylideneaniline ( SA ) derivatives 1–3 were prepared to study the substituent effect on the chromic properties. Compounds 1 and 3 , introduced naphthyl group on the A ring in the parent compound SA , exhibited the solvatochromism, thermochromism and photochromism, while compound 2 , introduced the naphthyl group on the B ring in SA , did not show the solvatochromism or thermochromism. The discussion in this study is mainly focused on the behaviour of compounds 1 and 2 . The UV absorption spectra of 1 dramatically changed with increasing the solvent polarity as well as cooling temperature, suggesting that 1 takes Z -NH form in polar solvents at room temperature or even in non-polar solvents at below 120 K. Compound 1 emits fluorescence (FL) only at low temperature with small Stokes shift, while 2 exhibits fluorescence emission with considerably large Stokes shift. On UV irradiation, 1 in benzene underwent intramolecular hydrogen atom transfer to give E -NH form. The large Stokes shift observed in 2 indicates that 2 takes E -OH form even at low temperature in any solvents, and underwent intramolecular hydrogen atom transfer in the excited state to give Z -NH form, which emits the fluorescence at low temperature, or undergoes isomerization around CC double bond to give E -NH form. The potential energy diagrams for 1 and 2 were also determined.
146 citations
TL;DR: Reactions with natural acyl chains indicate the involvement of a highly reactive diiron intermediate capable of oxidizing secondary C-H bonds, but also capable of diagnostic O-atom transfer reactions with the appropriate substrate analogues.
Abstract: Stearoyl-acyl carrier protein Delta(9) desaturase (Delta9D) produces oleic acid, a nutritionally valuable fatty acid containing a cis double bond between C-9 and C-10. This multiprotein diiron enzyme complex reacts with stearoyl-acyl carrier protein, reduced [2Fe-2S] ferredoxin, and O(2) to complete the highly regiospecific and stereoselective desaturation reaction. Interactions with the acyl chain provide stability to the enzyme-substrate complex, give an energetic contribution to catalytic selectivity, and help to order the electron transfer, O(2) binding, and C-H bond cleavage steps of catalysis. Reactions with natural acyl chains indicate the involvement of a highly reactive diiron intermediate capable of oxidizing secondary C-H bonds (bond dissociation energy approximately 95 kcal/mol), but also capable of diagnostic O-atom transfer reactions with the appropriate substrate analogues. For soluble Delta9D, the natural reaction may initiate at the C-10 position, in contrast to the well-established initial reactivity of the membrane enzyme homologue stearoyl-coenzyme A (CoA) Delta(9) desaturase at the C-9 position.
145 citations
TL;DR: These experiments all confirm the basic hypothesis that trans fatty acids produce membrane properties more similar toThose of saturated chains than to those of acyl chains containing cis double bonds; i.e., cis double Bonds induce much larger membrane perturbations than trans double bonds.
Abstract: The ever-increasing amount of trans fatty acids in the human diet has been linked to a variety of afflictions, most notably coronary heart disease and arteriosclerosis. The mechanism of why the replacement of cis fatty acids with their trans counterparts can be detrimental to the health of an individual remains a mystery. Here, we compare the differences in membrane physical properties including molecular dynamics, lateral lipid packing, thermotropic phase behavior, "fluidity", lateral mobility, and permeability between model membranes (lipid monolayers and bilayers) composed of cis- and trans-containing phosphatidylcholines (PCs). The PCs tested have a total of zero, one, two, or four cis (oleic or linoleic) or trans (elaidic or linoelaidic) double bonds. These experiments all confirm the basic hypothesis that trans fatty acids produce membrane properties more similar to those of saturated chains than to those of acyl chains containing cis double bonds; i.e., cis double bonds induce much larger membrane perturbations than trans double bonds.
141 citations
TL;DR: Of the various levels of theory tried, MP2 calculations with a triple-zeta-valence basis set were found to be the most effective for providing reliable results.
Abstract: The 1H and 13C NMR spectra of a number of push−pull alkenes were recorded and the 13C chemical shifts calculated employing the GIAO perturbation method. Of the various levels of theory tried, MP2 calculations with a triple-ζ-valence basis set were found to be the most effective for providing reliable results. The effect of the solvent was also considered but only by single-point calculations. Generally, the agreement between the experimental and theoretically calculated 13C chemical shifts was good with only the carbons of the carbonyl, thiocarbonyl, and cyano groups deviating significantly. The substituents on the different sides of the central CC partial double bond were classified qualitatively with respect to their donor (S,S < S,N < N,N) and acceptor properties (C≡N < CO < CS) and according to the ring size on the donor side (6 < 7 < 5). The geometries of both the ground (GS) and transition states (TS) of the restricted rotation about the central CC partial double bond were also calculated at the HF ...
131 citations
TL;DR: In this article, a simple qualitative molecular orbital diagram is presented to describe the possible π-interactions of (dxz, dyz) metal orbitals with axially coordinated ImH and periodate in six-coordinate Mn(Por), as the active oxidizing species.
Abstract: Highly selective epoxidation (>95%) of unfunctionalized alkenes was performed by tetrabutylammonium periodate in the presence of six different phenyl substituted manganese(III)
meso-tetraphenylporphyrins [Mn(Por)] and imidazole in CH2Cl2. Electron-withdrawing and bulky substituents on the phenyl groups lowered the catalytic activities of the corresponding Mn(Por). Less bulky alkenes with electron -rich double bonds showed greater reactivity in the epoxidation. Co-catalytic activities of four different classes of axial nitrogen donors are compared in the presence of various Mn(Por). In general no direct correlation was found between co-catalytic activities and the pKa values of the nitrogen donors. Strong σ-donor amines (pKa = 10.6 to 11.123) and weak π-donor pyridines (pKa = 5.25 to 6.65) showed comparable co-catalytic activities. Strong π-donor aminopyridines (pKa = 7 to 9.71) and imidazoles (pKa = 6.95 to 7.86) are generally much better co-catalysts than pure σ-donors, suggesting the importance of π-bonding interactions of the nitrogenous donors. N–H imidazoles with the possibility for N–H⋯B hydrogen bonding are much more effective co-catalysts than 1-methylimidazole. Methylpyridines and aminopyridines with substituents at the 2 or 2,6 positions showed particularly high co-catalytic activities toward manganese(III) meso-tetrakis(pentafluorophenylporphyrin) acetate. This “unusual” observation suggests the occurrence of some attractive hydrogen bonding interactions between ortho-fluorines of the manganese porphyrin and the substituents of these donors. A simple qualitative molecular orbital diagram is presented to describe the possible π-interactions of (dxz, dyz) metal orbitals with axially coordinated ImH and periodate in six-coordinate Mn(Por)(ImH)(IO4), as the active oxidizing species. A catalytic cycle is postulated in which the intermediate involves complexation of an alkene to the coordinated periodate, and attempts have been made to visualize the orbital interactions for this intermediate species.
118 citations
TL;DR: This work shows that relative SOA yields from ozonolysis of cyclic alkenes can be qualitatively predicted from properties of the parent hydrocarbons, and this prediction compares well to measurements of the SOA yield from the ozonallysis of terpinolene.
Abstract: The secondary organic aerosol (SOA) yields from the laboratory chamber ozonolysis of a series of cycloalkenes and related compounds are reported. The aim of this work is to investigate the effect of the structure of the hydrocarbon parent molecule on SOA formation for a homologous set of compounds. Aspects of the compound structures that are varied include the number of carbon atoms present in the cycloalkene ring (C_5 to C_8), the presence and location of methyl groups, and the presence of an exocyclic or endocyclic double bond. The specific compounds considered here are cyclopentene, cyclohexene, cycloheptene, cyclooctene, 1-methyl-1-cyclopentene, 1-methyl-1-cyclohexene, 1-methyl-1-cycloheptene, 3-methyl-1-cyclohexene, and methylenecyclohexane. The SOA yield is found to be a function of the number of carbons present in the cycloalkene ring, with an increasing number resulting in increased yield. The yield is enhanced by the presence of a methyl group located at a double-bonded site but reduced by the presence of a methyl group at a non-double-bonded site. The presence of an exocyclic double bond also leads to a reduced yield relative to that of the equivalent methylated cycloalkene. On the basis of these observations, the SOA yield for terpinolene relative to the other cyclic alkenes is qualitatively predicted, and this prediction compares well to measurements of the SOA yield from the ozonolysis of terpinolene. This work shows that relative SOA yields from ozonolysis of cyclic alkenes can be qualitatively predicted from properties of the parent hydrocarbons.
TL;DR: The present photoinitiation procedure can be applied to the iodotrifluoromethylation of unsaturated compounds, when the xenon-lamp-irradiated reactions are conducted under the refluxing conditions of excess CF3-I.
Abstract: Dependent on the selection of the light sources employed, the photoinduced iodoperfluoroalkylation of a variety of unsaturated compounds takes place efficiently via a radical mechanism. Upon irradiation with a xenon lamp through Pyrex (hν >300 nm), terminal alkenes (R−CHCH2) and alkynes (R−C⋮CH) undergo iodoperfluoroalkylation with perfluoroalkyl iodides (RF-I) regioselectively, providing R−CH(I)−CH2−RF and R−C(I)CH−RF, respectively. In the case of terminal allenes (R−CHCCH2), the photoinduced iodoperfluoroalkylation occurs selectively at the terminal double bond, giving the corresponding β-perfluoroalkylated vinylic iodides (R−CHC(I)−CH2−RF) in good yields. The photoinitiated reaction of vinylcyclopropanes (c-C3H5−C(R)CH2) with RF-I proceeds via the rearrangement of cyclopropylcarbinyl radical intermediates to the homoallylic radical intermediates, and the corresponding 1,5-iodoperfluoroalkylated products (I−(CH2)2CHC(R)−CH2−RF) are obtained in high yields. Isocyanides (R−NC), as C−N unsaturated compound...
TL;DR: In this article, the role of steric bulk and π electron release within the ERn substituent in generating tractable borylene complexes has been probed, as has the nature of the counterion.
TL;DR: In this article, it was shown that with a suitably bulky bidentate ligand, three-coordinate, high-spin alkyl complexes of iron(II) are stable.
TL;DR: In this article, the catalytic properties of gold-supported catalysts for the liquid phase reduction of α,β-unsaturated ketones to the corresponding unsaturated alcohols were investigated.
TL;DR: It is proposed that arachidonic acid and its trans isomers can function as biomarkers in membranes for distinguishing the two trans fatty acid-forming pathways.
Abstract: Trans unsaturated fatty acids in humans may be originated by two different contributions. The exogenous track is due to dietary supplementation of trans fats and the endogenous path deals with free-radical-catalyzed cis−trans isomerization of fatty acids. Arachidonic acid residue (5c,8c,11c,14c−20:4), which has only two out of the four double bonds deriving from the diet, was used to differentiate the two paths and to assess the importance of a radical reaction. A detailed study on the formation of trans phospholipids catalyzed by the HOCH2CH2S• radical was carried out on l-α-phosphatidylcholine from egg lecithin and 1-stearoyl-2-arachidonoyl-l-α-phosphatidylcholine (SAPC) in homogeneous solution or in large unilamellar vesicles (LUVET). Thiyl radicals were generated from the corresponding thiol by either γ-irradiation or UV photolysis, and the reaction course was followed by GC, Ag/TLC, and 13C NMR analyses. The isomerization was found to be independent of cis double bond location (random process) in i-P...
TL;DR: Fourteen metathesis initiators that had been designed for use in the living polymerization of diethyl dipropargylmalonate (DEDPM), including the Hoveyda catalyst, were presented.
Abstract: Fourteen metathesis initiators that had been designed for use in the living polymerization of diethyl dipropargylmalonate (DEDPM), including the Hoveyda catalyst [RuCl(2)(IMesH(2))([double bond]CH-2-(2-PrO)[bond]C(6)H(4))] (1 a), as well as [Ru(CF(3)COO)(2)(IMesH(2))([double bond]CH-2-(2-PrO)[bond]C(6)H(4))] (1 b), [Ru(CF(3)CF(2)COO)(2)(IMesH(2))([double bond]CH-2-(2-PrO)[bond]C(6)H(4))] (1 c), [Ru(CF(3)CF(2)CF(2)COO)(2)(IMesH(2))([double bond]CH-2-(2-PrO)[bond]C(6)H(4))] (1 d), [RuCl(2)(IMesH(2))([double bond]CH-2,4,5-(MeO)(3)[bond]C(6)H(2))] (2 a), [Ru(CF(3)COO)(2)(IMesH(2))([double bond]CH-2,4,5-(MeO)(3)[bond]C(6)H(2))] (2 b), [Ru(CF(3)CF(2)COO)(2)(IMesH(2))([double bond]CH-2,4,5-(MeO)(3)[bond]C(6)H(2))] (2 c), [Ru(CF(3)CF(2)CF(2)COO)(2)(IMesH(2))([double bond]CH-2,4,5-(MeO)(3)[bond]C(6)H(2))] (2 d), [RuCl(2)(IMes)([double bond]CH-2-(2-PrO)[bond]C(6)H(4))] (3 a), [Ru(CF(3)COO)(2)(IMes)([double bond]CH-2-(2-PrO)[bond]C(6)H(4))] (3 b), [RuCl(2)(IMesH(2))([double bond]CH-2-(2-PrO)-5-NO(2)[bond]C(6)H(3))] (4 a), [Ru(CF(3)COO)(2)(IMesH(2))([double bond]CH-2-(2-PrO)-5-NO(2)[bond]C(6)H(3))] (4 b), [Ru(CF(3)CF(2)COO)(2)(IMesH(2))([double bond]CH-2-(2-PrO)-5-NO(2)[bond]C(6)H(3))] (4 c), and [Ru(CF(3)CF(2)CF(2)COO)(2)(IMesH(2))([double bond]CH-2-(2-PrO)-5-NO(2)[bond]C(6)H(3))] (4 d) (IMes=1,3-dimesitylimidazol-2-ylidene; IMesH(2)=1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) were prepared. Living polymerization systems could be generated with DEDPM by careful tuning of the electronic nature and steric placement of the ligands. Although 1 a, 2 a, 3 a, 3 b, and 4 a were inactive in the cyclopolymerization of DEDPM, and initiators 1 b-d did not allow any control over molecular weight, initiators 2 b-d and 4 b-d offered access to class VI living polymerization systems. In particular, compounds 2 b and 4 d were superior. The livingness of the systems was demonstrated by linear plots of M(n) versus the number of equivalents of monomer added (N). For initiators 2 b-d and 4 b-d, values for k(p)/k(i) were in the range of 3-7, while 1 b, 1 c, and 1 d showed a k(p)/k(i) ratio of >1000, 80, and 40, respectively. The use of non-degassed solvents did not affect these measurements and underlined the high stability of these initiators. The effective conjugation length (N(eff)) was calculated from the UV/Vis absorption maximum (lambda(max)). The final ruthenium content in the polymers was determined to be 3 ppm.
TL;DR: The results presented here provide quantitative insight into RNA catalysis and serve as a first step toward the construction of a high-level quantum database for development of new semiempirical Hamiltonian models for biological reactions.
Abstract: Density functional calculations of a series of metaphosphates, acyclic and cyclic phosphates and phosphoranes relevant to RNA catalysis are presented. Solvent effects calculated with three well-established solvation models are analyzed and compared. The structure and stability of the compounds are characterized in terms of thermodynamic quantities for isomerization and ligand substitution reactions, gas-phase proton affinities, and microscopic solution pK(a)() values. The large dataset of compounds allows the estimation of bond energies to determine the relative strengths of axial and equatorial P-O phosphorane single bonds and P-O single and double bonds in metaphosphates and phosphates. The relative apicophilicty of hydroxyl and methoxy ligands in phosphoranes are characterized. The results presented here provide quantitative insight into RNA catalysis and serve as a first step toward the construction of a high-level quantum database for development of new semiempirical Hamiltonian models for biological reactions
TL;DR: 5H-Alkyl-2-phenyl-oxazol-4-ones, a little-known heterocyclic ring system, are readily available via a microwave-assisted, sodium fluoride catalyst cyclization of mono-alpha-haloimides, which in turn are accessed by N-acylation of benzamides with alpha-bromo acid halides.
Abstract: 5H-Alkyl-2-phenyl-oxazol-4-ones, a little-known heterocyclic ring system, are readily available via a microwave-assisted, sodium fluoride catalyst cyclization of mono-alpha-haloimides, which in turn are accessed by N-acylation of benzamides with alpha-bromo acid halides. Terminally substituted allyl systems serve as excellent substrates for Mo-catalyzed asymmetric allylic alkylation. The resultant products are formed with excellent ees involving a catalyst derived from N,N'-bis-picolinamide of trans-1,2-diaminocyclohexane and cycloheptatriene molybdenum tris(carbonyl). In addition to benzenoid, nonbenzenoid aromatic and vinyl substituents on the allyl carbonate moiety provide good to excellent regio- and diastereoselectivity as well as excellent enantioselectivity. Substituents on the heterocycle include methyl, n-butyl, allyl, isobutyl, isopropyl, and cyclohexyl. The presence of a double bond in the product allows them to be further modified via the chemistry of the double-bond, including metathesis. The products are hydrolyzed under basic conditions to provide alpha-hydroxyamides.
TL;DR: The topological properties of the iminophosphorane illustrate that the formal P=N double bond is better written as a polar P(+)--N(-) single bond.
Abstract: The iminophosphorane Ph 2 P(CH 2 Py)(NSiMe 3 ) (1) was treated with deprotonating alkali metal reagents to give [(Et 2 O)Li{Ph 2 P(CH-Py)(NSiMe 3 )}] (2), {[Ph 2 P(CH 2 Py)(NSi-Me 3 )}Li{Ph 2 P(CHPy)(NSiMe 3 )}] (3) and [{Ph 2 P(CH 2 Py)(NSiMe 3 )}-Na{Ph 2 P(CHPy)(NSiMe 3 )}] (4). We report their coordination behaviour in solid-state structures and NMR spectroscopic features in solution. Furthermore, we furnish experimental evidence against hypervalency of the phosphorus atom in iminophosphoranes from experimental charge-density studies and subsequent topological analysis. The topological properties, correlated to the results from NMR spectroscopic investigations, illustrate that the formal P=N double bond is better written as a polar P + -N - single bond. Additionally, the effects of metal coordination on the bonding parameters of the iminophosphorane and the related anion are discussed.
Patent•
28 May 2004TL;DR: In this paper, a novel condensed ring compound has been proposed for regulating GPR40-receptor function and being useful as an insulin secretion promoter or as a preventive/therapeutic agent for diabetes mellitus.
Abstract: A novel condensed ring compound having the activity of regulating GPR40-receptor function and being useful as an insulin secretion promoter or as a preventive/therapeutic agent for diabetes mellitus, etc. More specifically, a condensed ring compound of the formula: (I) [wherein: Ar is a substituted or unsubstituted cyclic group; ring A is a further substituted or unsubstituted ring (provided that the ring is none of thiazole, oxazole, imidazole and pyrazole); each of Xa and Xb independently is a bond or a spacer of 1 to 5 main chain atoms; Xc is O, S, SO or SO2; is or ; ring B is a 5 to 7-membered ring; Xd is a bond, CH or CH2; ...... is a single bond when Xd is a bond or CH2, and a double bond when Xd is CH; and R1 is a substituted or unsubstituted hydroxyl] or a salt thereof.
TL;DR: In this paper, an N-acyliminium ion generated by thecation pool method adds to an electron-rich carbon−carbon double bond, such as enamine derivatives and vinyl sulfides, to form the second "cation pool" to create the corresponding three-component coupling products.
Abstract: Sequential one-pot three-component coupling reactions have been developed based on the “cation pool” method. An N-acyliminium ion generated by the “cation pool” method adds to an electron-rich carbon−carbon double bond, such as enamine derivatives and vinyl sulfides, to form the second “cation pool”. The addition of nucleophiles such as allylsilanes, enol silyl ethers, Grignard reagents, and organoaluminum compounds led to the formation of the corresponding three-component coupling products.
TL;DR: In this article, the global and local electrophilicity indexes have been used to characterize the reactivity pattern of the CC double bond towards nucleophilic addition reactions.
TL;DR: DSC studies and XRD measurements showed that the aqueous gel 1 maintains an interdigitated bilayered structure with 3.14 nm long-range ordering, and the corresponding organogel maintains an extended bilayer structure for 4.34 nm, indicating a clear difference in the aggregation behavior in different solvents.
Abstract: Structurally simple, renewable-resource-based cardanyl (glucoside)s [1, 1-O-3'-n-(pentadecyl) phenyl-beta-D-glucopyranoside; 2, 1-O-3'-n-(8'(Z)-pentadeceenyl)-beta-glucopyranoside; 3, 1-O-3'-n-(8'(Z),11'(Z)pentadecadienyl)phenyl-beta-D-glucopyranoside, 4; 1-O-3'-n-(8'(Z),11'(Z),14'-pentadecatrienyl)phenyl-beta-D-glucopyranoside; and the mixture 5] form thermally reversible transparent gels in a water/alcohol mixture and a number of organic solvents, strongly influenced by the unsaturation of the aliphatic alkyl chain. DSC studies revealed that the Tgel of 1 in water/ethanol (1:1, vol/vol) gel is 69.0 degrees C, while of the introduction of a single double bond reduces the value to 30.0 degrees C in the case of monoene 2, indicating that the stability of the gel is related to the number of double bonds on the lipophilic part of the gelator. Furthermore, XRD measurements showed that the aqueous gel 1 maintains an interdigitated bilayered structure with 3.14 nm long-range ordering, and the corresponding organogel maintains an extended bilayer structure for 4.34 nm, indicating a clear difference in the aggregation behavior in different solvents.
TL;DR: Unexpectedly, the unsaturated FAME and TAG samples were found to elute more slowly at higher temperatures, a result just the opposite to the usual temperature effect noted in gas and most liquid chromatography systems.
TL;DR: The remarkably stable SbF(6)(-) salts of the radical cations of bithiophene 1(2T) and terthiophene 2(3T) were obtained by one-electron oxidation of the neutral precursors with NO(+)SbF (6)(-), and their solid-state structures were determined by X-ray crystallography.
Abstract: The remarkably stable SbF(6)(-) salts of the radical cations of bithiophene 1(2T) and terthiophene 1(3T), completely surrounded by bicyclo[2.2.2]octene (BCO) units, were obtained by one-electron oxidation of the neutral precursors with NO(+)SbF(6)(-), and their solid-state structures were determined by X-ray crystallography. In these radical cations, the presence of quinoidal character was apparent, as shown by the increased planarity and by comparison of the bond lengths with those of the neutral precursors. The shortest intermolecular pi-pi distances in the crystal structure of 1(2T)(*)(+)SbF(6)(-) (distance between two sp(2) carbon atoms, 4.89 A) and 1(3T)(*)(+)SbF(6)(-) (distance between an sp(2) carbon and a sulfur atom, 3.58 A) were found to be longer than the sums of the van der Waals radii of the corresponding atoms. In accord with this, no apparent change was observed in ESR and UV-vis-NIR spectra of solutions of 1(2T)(*)(+) and 1(3T)(*)(+) upon lowering the temperature, indicating that the pi- (or sigma-) dimer formation is inhibited in solution as well as in the solid state. The dications 1(2T)(2+) and 1(3T)(2+) were generated with the stronger oxidant SbF(5) in CH(2)Cl(2) at -40 degrees C and characterized by NMR spectroscopy. In the (1)H NMR spectra, two conformers were observed for each dication of both 1(2T)(2+) (transoid (t) and cisoid (c)) and 1(3T)(2+) (t,t and c,t) at room temperature due to the high rotational barrier around the inter-ring bond(s) between thiophene rings, which was caused by the enhanced double bond character of these bonds following two-electron oxidation. This is supported by DFT calculations (B3LYP/6-31G(d)), which predicted the rotational barriers in the dications of unsubstituted bithiophene and terthiophene to be 27.6 and 22.9 kcal mol(-)(1), respectively. In the case of quaterthiophene and sexithiophene surrounded by BCO frameworks 1(4T) and 1(6T), oxidation with even one molar equivalent of NO(+)SbF(6)(-) afforded the dication salts 1(4T)(2+)2SbF(6)(-) and 1(6T)(2+)2SbF(6)(-), which were isolated as stable single crystals and allowed the X-ray crystallography. In their crystal structures, the cationic pi-systems became planar again due to the great contribution of quinoidal resonance structures, and the pi-systems, which were arrayed in a parallel geometry, were also segregated by the steric effect of BCO units. The degree and tendency of changes in the bond lengths of thiophene rings of 1(4T)(2+) and 1(6T)(2+) as compared with neutral precursors were similar to those of 1(2T)(*)(+)SbF(6)(-) and 1(3T)(*)(+)SbF(6)(-), respectively, implying that the contribution of quinoidal character is modulated by the amount of positive charge per thiophene unit.
TL;DR: The stereochemical course of the oxidation of chiral oxazolidinone-substituted enecarbamates has been studied for singlet oxygen ((1)O(2), dimethyldioxirane (DMD), and m-chloroperbenzoic acid (mCPBA) by examining of the special structural and stereoelectronic features of the enecbamates.
Abstract: The stereochemical course of the oxidation of chiral oxazolidinone-substituted enecarbamates has been studied for singlet oxygen (1O2), dimethyldioxirane (DMD), and m-chloroperbenzoic acid (mCPBA) by examining of the special structural and stereoelectronic features of the enecarbamates. Valuable mechanistic insight into these selective oxidations is gained. Whereas the R1 substituent on the chiral auxiliary is responsible for the steric shielding of the double bond and determines the sense of the π-facial diastereoselectivity, structural characteristic such as the Z/E configuration and the nature of the R2 group on the double bond are responsible for the extent of the diastereoselectivity. Stereoelectronic steering by the vinylic nitrogen functionality controls the mode selectivity (ene reaction vs [2+2] cycloaddition) in the case of 1O2.
TL;DR: Several mechanisms have been examined in detail using DFT(B3PW91) calculations and are discussed for this H/F exchange: (a) internal olefin insertion/beta-fluoride elimination, (b) external ole Finney insertion/ beta- fluoride Elimination, and (c) F/H metathesis from either an inside or outside approach.
Abstract: Cp*(2)ZrH(2) (1) (Cp* = pentamethylcyclopentadienyl) reacts with perfluoropropene (2) to give Cp*(2)ZrHF (3) and hydrodefluorinated products under very mild conditions. Initial C-F bond activation occurs selectively at the vinylic terminal position of the olefin to exchange fluorine for hydrogen. Subsequent hydrodefluorination leads to the formation of the n-propylhydride complex Cp*(2)ZrH(CH(2)CH(2)CH(3)), which can be cleaved with dihydrogen to give propane and 1. A theoretical study of the reaction of Cp*(2)ZrH(2) (Cp* = cyclopentadienyl) and CF(2)[double bond]CF(CF(3)) has been undertaken. Several mechanisms have been examined in detail using DFT(B3PW91) calculations and are discussed for this H/F exchange: (a) internal olefin insertion/beta-fluoride elimination, (b) external olefin insertion/beta-fluoride elimination, and (c) F/H metathesis from either an inside or outside approach. Of these, the first case is found to be energetically preferred. Selective defluorination at the terminal carbon has been shown to be favored over defluorination at the substituted and allylic carbons.
TL;DR: A three-step diversityoriented synthetic pathway based on reactive dihydroisoquinoline and dihydropyridine intermediates, which undergo a variety of transformations to generate skeletally diverse alkaloid-like compounds from simple, readily available starting materials is reported.
Abstract: Herein we report a new diversity-oriented synthetic pathway to skeletally diverse alkaloid-like compounds from simple, readily available starting materials. The synthetic strategy involves the generation and isolation of reactive, otherwise unstable dihydropyridines and dihydroisoquinolines on a solid support. A variety of reactions can be performed with the enamine double bond present in the isolated reactive intermediates, thus leading to skeletally diverse alkaloid-like products. Small molecules used in chemical genetic screens can be synthesized with guidance from compounds known to have biological activity or with the desire to distribute the products in chemical descriptor space. In the latter case, it may be advantageous to maximize the representation of different functional groups and conformations in a screen, since in most cases the nature of the small-molecule–target interaction can not be foreseen. Whereas complex molecules with many distinct appendages can be synthesized efficiently by using complexity-generating reactions and appending processes, there have been limited examples of synthetic pathways that yield products with a high degree of skeletal diversity. Herein we report a three-step diversityoriented synthetic pathway (Figure 1) based on reactive dihydroisoquinoline and dihydropyridine intermediates, which undergo a variety of transformations to generate skeletally diverse alkaloid-like compounds. We anticipated that the enamine moiety contained in dihydropyridines and dihydroisoquinolines could be targeted selectively to undergo a variety of transformations known to
TL;DR: Results, the kinetic data, the comparison of the catalytic rates with those for the stoichiometric reactions, and kinetic isotope effects indicate that the oxygen transfer from a dinuclear peroxotungstate to the double bond is the rate-limiting step for terminal allylic alcohols such as 2-propen-1-ol.
Abstract: The highly chemo-, regio-, and diastereoselective and stereospecific epoxidation of various allylic alcohols with only one equivalent of hydrogen peroxide in water can be efficiently catalyzed by the dinuclear peroxotungstate, K2[[W(=O)(O2)2(H2O)]2(mu-O)]2H2O (I) The catalyst is easily recycled while maintaining its catalytic performance The catalytic reaction mechanism including the exchange of the water ligand to form the tungsten-alcoholate species followed by the insertion of oxygen to the carbon-carbon double bond, and the regeneration of the dinuclear peroxotungstate with hydrogen peroxide is proposed The reaction rate shows first-order dependence on the concentrations of allylic alcohol and dinuclear peroxotungstate and zero-order dependence on the concentration of hydrogen peroxide These results, the kinetic data, the comparison of the catalytic rates with those for the stoichiometric reactions, and kinetic isotope effects indicate that the oxygen transfer from a dinuclear peroxotungstate to the double bond is the rate-limiting step for terminal allylic alcohols such as 2-propen-1-ol (1a)