One-way EZ-isomerization of bis(n-butylammonium) (Z,Z)-muconate under photoirradiation in the crystalline state

One-way EZ-isomerization of bis(n-butylammonium) (Z,Z)-muconate [(Z,Z)-hexa-2,4-diene-1,6-dioate] to the corresponding (E,E)-isomer quantitatively proceeded in the crystalline state under photoirradiation with a high-pressure mercury lamp, being a new type of crystal-to-crystal reaction.     

Quantitative analyses of shape-selective intercalation of isomeric mixtures of muconates into [LiAl2(OH)6]Cl.yH2O layered double hydroxide

Quantitative investigation of the shape selectivity for the competitive intercalation reaction of isomeric mixtures in the interlayer of LDH was achieved by analyzing the solid phases synthesized by the reaction of [LiAl(2)(OH)(6)]Cl.yH(2)O with various compositional mixtures of (E,E)- and (Z,Z)-muconates. The apparent partition constant K' for the anion-exchange reaction between (E,E)- and (Z,Z)-muconates was quite dependent on the mole fraction of muconates in solution. The only single phase saturated with [LiAl(2)(OH)(6)](2)[(E,E)-C(6)H(4)O(4)].zH(2)O could be obtained in the range of the initial mole fraction of (E,E)-muconate larger than 0.6 in the starting solution, while mixed phases intercalated with (E,E)- and (Z,Z)-muconates could be obtained at lower mole fractions of (E,E)-muconate. The shape selectivity for the competitive reaction of two muconates on the [LiAl(2)(OH)(6)](+) lattice could be ascribed to thermodynamic processes, and the conditions under which that pure (E,E)-muconate was efficiently separated from isomeric mixtures of two muconates were successfully evaluated.     

Chemistry of the diazeniumdiolates: Z right harpoon over left harpoon E isomerism

Here, we explore the chemistry of the previously undocumented E form of diazeniumdiolates having the structure R(1)R(2)NN(O)=NOR(3). Reported crystallographic studies have uniformly revealed the Z configuration, and our attempts to observe a Z --> E conversion through thermal equilibration or photochemical means have, until now, consistently failed to reveal a significant amount of a second conformer. As a typical example, the NMR spectrum of trimethyl derivative Me(2)NN(O)=NOMe revealed no evidence for a second configuration. Electronic structure calculations attribute this finding to a prohibitively high interconversion barrier of approximately 40 kcal/mol. A similar result was obtained when we considered the case of R(1) = Me = R(3) and R(2) = H at the same levels of theory. However, when MeHNN(O)=NOMe was ionized by dissociating the N-H bond, the barrier was calculated to be lower by approximately 20 kcal/mol, with the E form of the anion being favored over Z. This circumstance suggested that an E isomer might be isolable if a Z anion were formed and given sufficient time to assume the E configuration, then quenched by reaction with an electrophile to trap and neutralize the E form and restore the putatively high interconversion barrier. Consistent with this prediction, basifying iPrHNN(O)=NOCH(2)CH(2)Br rapidly led to a six-membered heterocycle that was crystallographically characterized as containing the -N(O)=NO- functional group in the E configuration. The results suggest an approach for generating pairs of Z and E diazeniumdiolates for systematic comparison of the rates at which the individual isomers release bioactive NO and of other physicochemical determinants of their biomedical utility.     

New synthesis of (Z,E)-2,7-bis(4-cyanobenzylidene)cycloheptan-1-one under stereospecific constraints induced by host-guest interactions

A selective, efficient, and fast access to (Z,E)-2,7-bis(4-cyanobenzylidene)cycloheptan-1-one (BCBCH), precursor of the synthetic antagonist of tissue-plasminogen activator (t-PA), is reported using a solid/solid aldolisation-crotonisation reaction on a supramolecular complex under microwave irradiation. The underlying mechanism is investigated from the crystal structure of the intermediate host-guest complex formed between permethylated gamma-cyclodextrin and (Z)-2-(4-cyanobenzylidene)cycloheptan-1-one.     

Synthesis and Crystal Structure of the Optical Activity of （Z）-Nitromethylene Neonicotinoid Analogue

A novel (Z)-nitromethylene neonicotinoid analogue (C23H27Cl2N5O4·2H2O) (II) with optical activity has been synthesized, the structure was characterized by elemental analysis, IR and 1H NMR spectra, and the (Z)-configuration was confirmed by single-crystal X-ray diffraction. The crystal belongs to triclinic, space group P1 with a = 7.4638(3), b = 12.6232(5), c = 15.2990(6), α = 71.907(1), β = 89.397(2), γ = 80.314(1)°, V = 1349.28(9)3, Z = 2, Dc = 1.340 g/cm3, μ = 0.286 mm-1, Mr = 544.43, F(000) = 572, S = 1.056, R = 0.0801 and wR = 0.2366 for 4998 unique reflections with 3012 observed ones (I > 2σ(I)). In the crystal, the dihedral angle between the pyridine and 4-Cl-phenyl rings is 58.13°. Intermolecular O–H···O, C–H···O and C–H···Cl hydrogen bonds involving water molecules stabilize the crystal structure.     

Stereoselective preparation of (E)- and (Z)-alpha-fluorostilbenes via palladium-catalyzed cross-coupling reaction of high E/Z ratio and (Z)-1-bromo-1-fluoroalkenes

A highly stereoselective method to prepare both (E)- and (Z)-alpha-fluorostilbenes is described. 1-Bromo-1-fluoroalkenes (E/Z approximately 1:1), a readily available starting material, isomerizes to high E/Z ratios by storage at -20 degrees C or by photolysis at 254 nm. Stille coupling between these high E/Z 1-bromo-1-fluoroalkenes and aryl stannanes gave (Z)-alpha-fluorostilbenes in high stereoselectivity. (Z)-1-Bromo-1-fluoroalkenes, which were kinetically separated from 1-bromo-1-fluoroalkenes (E/Z approximately 1:1), can participate in Suzuki coupling reactions to give (E)-alpha-fluorostilbenes stereoselectively.     

Crystalline-state Z,E-photoisomerization of a series of (Z,E,Z)-1,6-diphenylhexa-1,3,5-triene 4,4'-dicarboxylic acid dialkyl esters. Chain length effects on the crystal structure and photoreactivity

[reaction: see text] Crystalline-state Z,E-photoisomerization of a series of (Z,E,Z)-1,6-diphenylhexa-1,3,5-triene 4,4'-dicarboxylic acid dialkyl (R) esters [(Z,E,Z)-1a, R = Me; (Z,E,Z)-1b, R = Et; (Z,E,Z)-1c, R = n-Pr; (Z,E,Z)-1d, R = n-Bu] was investigated. All Z,E,Z isomers underwent one-way isomerization to the corresponding E,E,E isomers. The reaction efficiency was strongly enhanced as the length of the alkyl chain increased. Single-crystal X-ray analyses of (Z,E,Z)-1a-d showed that the alkyl chain part of the crystals became larger as the chain length increased. The conformational flexibility of the alkyl chains made the large change in the triene geometry in the lattice possible, leading to the enhancement of the photoreactivity in the crystalline state.     

对甲氧基苯甲醛肟晶体结构、红外光谱及分子间相互作用的实验与理论研究

从实验和理论两个方面研究了Z型和E型对甲氧基苯甲醛肟晶体的熔点、 结构、 红外光谱和分子间相互作用. 在E型和Z型晶体中, 对甲氧基苯甲醛肟分子分别呈二聚体重复单元和双链Zigzag结构排列. 研究结果表明, 电荷分布变化引起的静电相互作用差别、 形成氢键的方式和强度以及晶体中分子排列方式导致的范德华作用不同是造成Z型和E型对甲氧基苯甲醛肟固体熔点、 红外光谱等物理性质差别的根本原因.     

Synthese der (1Z,3E) und (1Z,3Z)-isomeren des wisanins

The (1Z,3E)- and (1Z,3Z)-isomers of wisanine were synthesized and characterized by their spectroscopic data.     

Experimental and Computational Studies of the Isomerization between Z and E Isomers of Benzaldoximes

The isomerization between Z and E isomers of benzaldoximes in different solvents were measured by TLC method. The experimental results show that acid solvents catalyze this inter‐conversion process dramatically. Solution state NMR measurements also show very different spectra for Z and E isomers of benzaldoximes in different solvents. All this suggests that the acidity of solvent is a very important factor to affect the inter‐conversion process. Theoretical investigations of Z to E inter‐conversion of benzaldoximes in different solvents were carried out by DFT calculations at B3LYP/6–3 11+G** level. The calculations show that the barrier from Z to E in the presence of acid is much lower than that without acid. This agrees with the experimental data very well. The calculated structure in the transition state is helpful for the understanding of the inter‐conversion mechanism.     

Synthesis of the N-((1E)-alkenyl)-(2Z,4Z)-heptadienamide side chain of salicylihalamide A and apicularens A and B

[reaction: see text] The unstable N-((1E)-alkenyl)-(2Z,4Z)-heptadienamide side chain of salicylihalamide A (1) and apicularens A and B (3 and 4) has been prepared in one pot by the addition of (1Z,3Z)-hexadienylcuprate, prepared in situ from EtLi, CuBr.SMe2, and acetylene, to a (1 E)-alkenyl isocyanate.     

Crystal engineering for topochemical polymerization of muconic esters using halogen-halogen and CH/pi interactions as weak intermolecular interactions

We now report the molecular and crystal structure design of muconic ester derivatives on the basis of crystal engineering using halogen-halogen contacts and CH/pi interactions. The solid-state photoreaction pathway of the dibenzyl (Z,Z)-muconates as the 1,3-diene dicarboxylic acid monomers depends on the structure of the ester groups. The substitution of a halogen atom for the aromatic hydrogen of a benzyl group induces topochemical polymerization to produce stereoregular polymers in a crystalline form, whereas the unsubstituted benzyl derivative isomerizes to yield the corresponding E,E isomer under similar conditions. The topochemical polymerization process is directly confirmed by the fact that the single-crystal structures before and after the polymerization are very similar to each other. From the crystal structure analysis for a series of substituted benzyl (Z,Z)- and (E,E)-muconates, it has been revealed that the planar diene moieties are closely packed to form a columnar structure in the crystals. The stacking of the polymerizable monomers is characterized by a stacking distance of 4.9-5.2 A along the columns. This structure is supported by a halogen-halogen interaction between the chlorine or bromine atoms introduced at the p position of the benzyl groups in addition to an aromatic stacking due to the CH/pi interaction between the benzylic methylene hydrogens and aromatic rings. The design of a monomer packing corresponds to the type and position of the introduced halogen atom and also the polymorphs. To make a stacking distance of 5 A using both halogen-halogen and CH/pi interactions as supramolecular synthons is important for the molecular design of muconic ester derivatives appropriate for topochemical polymerization.     

E versus Z Diazeniumdiolation of Acetoacetate-Derived Carbanions

Nitric oxide adds to methyl acetoacetate in the presence of KOH in methanol at room temperature to form potassium acetylsydnonate N-oxide (K1) with an (E)-diazeniumdiolation and potassium acetate diazenium diolate (K(2)2) from a (Z)-diazeniumdiolation. A study of the reaction with LiOH, NaOH, and NMe(4)OH and with ethyl acetate substrate reveals that the temperature of the reaction greatly influences the nitric oxide reactivity. At 23 °C, nitric oxide adds to give both E and Z products, whereas at -5 °C the gas reacts almost exclusively to give Z addition. The (Z)-diazeniumdiolation products, namely, the alkali metal and NMe(4)(+) salts of methyl and ethylbutenoate-2-diazeniumdiolate-3-hydroxylate (3(2-) and 4(2-)), are isolated in good yields. The alkali metal salts are not amenable for recrystallization because of their ready decomposition in aqueous solutions. However, [NMe(4)](2)[MeC(O)C(N(2)O(2))CO(2)Me] is readily recrystallized from a methanol/acetonitrile solvent mixture. The crystals are unambiguously characterized by X-ray crystallography. NMR spectra for all of the 3(2-) and 4(2-) salts reveal the presence of two isomers in aq solutions. But the structure of the NMe(4)(+) salt contains only one of the isomers. Our attempts to cyclize the isolated and purified butenoatediazeniumdiolates from the (Z)-diazeniumdiolation to the E-containing sydnonate products were unsuccessful. TGA/DSC data for all of the products demonstrate the thermal instability of the salts at high temperatures. The salts decompose exothermally possibly with the release of N(2)O among other gases.     

(Z)-2-羟基-3-苯甲酰丙烯酸甲酯的合成及晶体结构

标题化合物C11H10O4的晶体结构用X-射线单晶衍射法测定。晶体属单斜晶系, P21/c空间群, 晶胞参数a = 12.136(1), b = 5.559(1), c = 14.615(2) ? b = 96.758(3), V = 979.1(3) ?, Z = 4, Mr = 206.19, Dc = 1.399 g/cm3, F(000) = 432, m(MoKa) = 0.107 mm-1。晶体结构用直接法解出, 经全矩阵最小二乘法对原子参数进行修正, 最终的偏离因子为R = 0.0453, wR = 0.0990。标题化合物形成了1个大的共轭体系, 含有1个稳定的烯醇结构。结构测定表明还存在着1个分子内氢键的结构, 它使烯醇结构更加稳定。     

Highly stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters and (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated amides from 1-bromo-1-fluoroalkenes via palladium-catalyzed carbonylation reactions

The highly stereoselective synthesis of (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated esters and (E)- and (Z)-alpha-fluoro-alpha,beta-unsaturated amides is described. 1-Bromo-1-fluoroalkenes (E/Z approximately 1:1), which are readily available starting materials, have been found to isomerize to high E/Z ratios after storage at -20 degrees C for 1 week or by photolysis at 254 nm. Since the (E)-isomers have been found to react faster than the corresponding (Z)-isomers at room temperature in Pd(0)-catalyzed reactions, the palladium-catalyzed carboalkoxylation of high E/Z 1-bromo-1-fluoroalkenes lead to a high Z/E (Z/E >/= 98:2) ratio of the alpha-fluoro-alpha,beta-unsaturated esters. When 1-bromo-1-fluoroalkenes (E/Z approximately 1:1) were reacted with HCOOH/NBu(3)/Pd(II)/DMF, the (E)-isomer was selectively reduced, and the remaining (Z)-1-bromo-1-fluoroalkenes were recovered in essentially pure isomeric form. The resulting mixture of (Z)-1-bromo-1-fluoroalkenes and the reduced products underwent similar palladium-catalyzed carboalkoxylation reactions at 70 degrees C, and the (E)-alpha-fluoro-alpha,beta-unsaturated esters were stereospecifically obtained. This methodology was also successfully applied for the stereospecific synthesis of (Z)- and (E)-alpha-fluoro-alpha,beta-unsaturated amides: the palladium-catalyzed carboamidation reaction of high E/Z and (Z)-1-bromo-1-fluoroalkenes lead to pure (Z)- and (E)-alpha-fluoro-alpha,beta-unsaturated amides, respectively.     

Stereoselective synthesis of (Z)-alkene-containing proline dipeptide mimetics

In peptides and proteins, the peptide bond between an amino acid and proline exists as an equilibrium mixture of the cis-imide and trans-imide due to the low energy barrier in their interconversion. This feature greatly influences the structure and function of the proline-containing peptides and proteins. Therefore, restricting the amide bond with an (E)- or (Z)-alkene should provide a promising method for elucidating the structure-activity relationships of the peptide and the proteins. In this report, the regio- and stereoselective synthesis of cis-alanylproline (Ala-Pro) type (Z)-alkene dipeptide mimetic is described. The key steps of this synthesis are to introduce a C3 unit onto a gamma-phosphoryloxy-alpha,beta-unsaturated-delta-lactam with an organocopper-mediated anti-S(N)2' reaction and subsequently construct a five-membered proline-like cyclic structure with an intramolecular Suzuki coupling reaction. Hydrolysis of the amide bond in the resulting bicyclic lactam yields the desired cis-Ala-Pro type (Z)-alkene dipeptide isostere. The presented synthetic methodology should be applicable to the general syntheses of other cis-aminoacylproline type (Z)-alkene dipeptide mimetics.     

(Z)-3-三苯基锡基-1,1-二苯基烯丙醇的合成、晶体结构和性质研究

合成并表征了5种新的有机锡化合物.测定了(Z)-3-三苯基锡基-1,1-二苯基烯丙醇的晶体结构.晶体属于P2₁/n空间群,晶胞参数α=1.2357(3)nm,6=0.9874(2)nm,c=2.2081(2)nm,β=95.23(3).,z-4.分子结构是以锡为中心的畸变四面体构型,双键为顺式构型.并对其性质进行了研究.     

Synthesis and reactivity of E,Z butadiene-iron tricarbonyl complexes.

The synthesis, structure and thermal stability of the E,Z butadiene-iron tricarbonyl complex 1 is reported. This complex reacts with organometallic nucleophiles in a stereoselective synthesis of functionalized E,Z dienes.     

Single-crystal-to-single-crystal E-->Z and Z-->E isomerizations of 3-chloroacrylic acid within the nanocavities of a supramolecular framework

Single-crystal-to-single-crystal E-->Z and Z-->E photo-isomerizations of 3-chloroacrylic acid (HClA) take place with full retention of the crystal lattice in the framework cavities of the supramolecular crystals CECR.HClA.2MeOH.1.5H(2)O (CECR = C-ethylcalix[4] resorcinarene); their progress has been monitored as the reaction proceeds.     

The kinetics of Z/E isomerization of methyl oleate catalyzed by photogenerated thiyl radicals.

The reaction of beta-mercaptoethanol with methyl oleate in tertbutyl alcohol was investigated under photochemical conditions. The time-dependent Z/E isomerization of the unsaturated moiety as well as the thiol-adduct formation were analyzed on the basis of radical generation rates and established rate constants. This provides precise room-temperature rate constants for the reversible thiyl radical addition to both Z and E isomers. The rate constants for HOCH2CH2S* addition to the Z and E forms were found to be 1.6 x 10(5) and 2.9 x 10(5) M(-1) S(-1), respectively. For the beta-elimination of the thiyl radical from the alkyl radical adduct, the rate constants were 1.7 x 10(7) and 1.6 x 10(8) S(-1), the faster associated with the formation of the E isomer. DFT-BB1K calculations on 2-butene assign this large preference of fragmentation for the E isomer to a lower activation barrier for the formation of the E transition state from the equilibrium radical adduct structure.