Theoretical study of the imidazolidinone catalyzed 1,4-addition of N,N-dimethyl-3-anisidine with α,β-unsaturated butyric aldehyde

Friedel–Crasfts alkylation reactions of α,β-unsaturated butyric aldehydes with N,N-dimethyl-3-anisidine catalyzed by a (2S,5S)-5-benzyl-2-tert-butyl-3-methylimidazolidin-4-one HCl salt have been carried out at the PCM(CH₂Cl₂)/B3LYP/6-311++G(d,p)//B3LYP/6-31G(d) level. Three reaction processes have been characterized: (I) the formation of an iminium ion intermediate; (II) the 1,4-iminium addition of the iminium ion; and (III) the hydrolysis of the addition product. Moreover, Path 1-1 is the favorable channel in the formation of the iminium ion. From the point of view of energy, the enantioselectivity is controlled by the carbon–carbon bond formation step that is involved in both the intermediate M4 and the transition state TS4. The highest energy barrier of the reaction is the H2 proton transfer from the O10 atom of a water molecule to the N1 atom of the catalyst in the hydrolysis process, which is 23.4 kcal/mol. The presented calculated results may be helpful in understanding the experimental product distribution for the title reaction, and provide a general model to help explain the mechanisms of similar reactions.     

Unexpected fluorous solvent effect on oxidation of 1-thioglycosides

Oxidation of various 1-thioglycopyrano- and furanosides with H₂O₂/Ac₂O/SiO₂ was performed in CH₂Cl₂/aprotic perfluorinated solvent mixtures (100:0 to 1:19, v/v). Reactions appeared much faster at a solvent ratio of 1:1 without significant over-oxidation to sulfones and modification of diastereoselectivity. Nevertheless, the nature of both the glycosyl moiety and the protecting group influenced the (S_S):(R_S) product ratio.     

A concise and efficient synthesis of tetrahydroquinoline alkaloids using the phase transfer mediated Wittig olefination reaction

The present study describes the total synthesis of 1,2,3,4-tetrahydroquinoline alkaloids (±)-galipinine, (±)-cuspareine, (±)-galipeine and (±)-angustureine, in three steps and high yields (78%, 76%, 74%, and 66%, respectively) from common aldehyde and the ylide respectives. The key step of this approach is based on an unusual Wittig reaction by using the phase transfer medium (aq. NaOH/CH₂Cl₂ 1:1 or t-BuOK/t-BuOH/CH₂Cl₂ 1:1), affording olefinic intermediates in high yields.     

The first example of hydrozirconation of alkynes in room temperature ionic liquids

Hydrozirconation of terminal alkynes in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]) at 30 °C gave highly regio- and stereoselectively (E)-vinylzirconium complexes, which underwent a cross-coupling reaction with aryl halides in the presence of Pd(PPh₃)₄ to afford (E)-1,2-disubstituted ethenes in good to high yields. Our system not only avoids the use of easily volatile THF or CH₂Cl₂ as solvent but also solves the basic problem of palladium catalyst reuse.     

The highly stereoselective decarboxylation of (+)-1-bromo-1-chloro-2,2,2-trifluoropropanoic acid to give (+)-1-bromo-1-chloro-2,2,2-trifluoroethane [(+)-halothane] with retention of configuration

The absolute configuration of the title acid 2 has been determined to be S by X-ray crystallography. Thus, decarboxylation of 2 produces (S)-(+)-halothane with 99% retention of configuration. This behavior is compared to other stereoselective decarboxylation reactions of α-haloacids from the literature that also gave high degrees of retention of configuration when in the form of their quaternary ammonium salts, which contain one proton. The proton of the ammonium salt is necessary in order to protonate the anionic intermediate formed from decarboxylation. In the absence of this relatively acidic proton, we had previously found that using triethylene glycol (TEG) as both the solvent and proton source for the decarboxylation reaction of acid 2 caused poor stereoselectivity. This was in contrast to 1,2,2,2-tetrafluoro-1-methoxypropionic acid 6, which showed a high degree of retention of configuration in TEG. In order to rationalize this differing behavior, we report DFT studies at PCM-B3LYP/6-31++G⁷ level of theory (the results were additionally confirmed with 6-311++G⁷ and aug-cc-pVDZ basis sets). The energy barrier to inversion of configuration of the anionic reaction intermediate 11 of acid 2 is 10.23 kcal/mol. However, we find that the anionic intermediate 10 from acid 6 would rather undergo β-elimination instead of inversion of configuration. Thus the planar transition state required for inversion of configuration is never reached, regardless of the rate of proton transfer to the anion.     

A synthetic approach toward taxol analogs: studies on the construction of the CD ring

Tricycle 6, containing the CD ring of taxol, is constructed from (S)-(+)-carvone in 21 steps involving a Diels-Alder reaction with isoprene, a Baeyer-Villiger oxidation, an Oppenaurer oxidation and Meerwein-Ponndorf-Verley reduction, a stereospecific Grignard addition, and an intramolecular S_N2 reaction as the key steps.     

Asymmetric synthesis of 3,4-dihydroxyglutamic acids via enantioselective reduction of cyclic meso-imide

Stereoselective synthesis of (3S,4S)- and (3R,4R)-series of 3,4-dihydroxyglutamic acids was investigated. The key reaction in this synthesis is asymmetric reduction of meso-imide derived from meso-tartaric acid. Lewis acid-promoted cyanation of the obtained optically active lactam via the acyliminium intermediate followed by standard deprotection procedure afforded the desired 3,4-dihydroxyglutamic acids.     

One-pot synthesis of imidazolines from aldehydes: detailed study about solvents and substrates

Imidazolines were prepared in one-pot operation from aldehydes and diamines through oxidation of aminal intermediates by NBS. This method could be applied to various aromatic and aliphatic aldehydes and N-nonsubstituted and N-monosubstituted 1,2-diamines. Furthermore, it was found that CH₂Cl₂ could be altered to TBME, a more environmentally friendly solvent, in the reaction using N-nonsubstituted 1,2-diamines. The reaction conditions were very mild and chemoselective.     

Application of axially dissymmetric ligand recoverable with fluorous solvent as a chiral auxiliary

(Ra)-(R)₂-2,2′-Bis(1-hydroxy-1H-perfluorooctyl)biphenyl ((Ra)-(R)₂-1c), which is an axially dissymmetric ligand with two chiral centers, works as a good chiral auxiliary for asymmetric aldol reaction. Thus, the reaction of monopropanoyl ester of 1c (2) with benzaldehyde in the presence of triethylamine and titanium(IV) chloride gave (2R),(3S)- and (2R),(3R)-3-hydroxy-2-methyl-3-phenylpropanoic acid esters (3a) in an approximate ratio of 4:1 in a total high yield. This result shows that stereoselectivity at 2-position is quite high, while that at 3-position is moderate. Both isomers were easily separated by column chromatography. Methanolysis of the separated isomers gave nearly quantitative recovery of 1c by extraction with a fluorous solvent without any loss of ee, while methyl (2R),(3S)- or (2R),(3R)-3-hydroxy-2-methyl-3-phenylpropanoates were obtained by CH₂Cl₂ extraction quantitatively in >99% ee. Aldol reaction of 2 with various aldehydes gave similar results.     

An efficient and simple Morita-Baylis-Hillman reaction based on the N-methylpyrrolidine-Ba(OH)2 catalytic system

By using of precise catalytic amount of N-methylpyrrolidine (5 mol %) and Ba(OH)₂ (1.5 mol %) in H₂O/CH₃OH 5/1 or CH₃OH/CH₂Cl₂ 3/1 solvent mixtures at T=0 °C a Morita-Baylis-Hillman derivatives could be obtained in good to excellent yield from 2-cyclopenten-1-one, 2-cyclohexen-1-one and formaldehyde and diverse aryl aldehydes after suitable reaction time.     

A novel one-pot synthesis of α-keto-1,3,4-oxadiazole derivatives based on isocyanide-Nef reaction

Various α-keto-1,3,4-oxadiazole derivatives were synthesized through a sequential intermolecular dehydrochlorination/intramolecular aza-Wittig reaction of carboxylic acids and imidoyl chloride intermediates, which were generated by isocyanide-Nef reaction of acyl chlorides and (N-isocyanimine) triphenylphosphorane (1) in CH₂Cl₂ at room temperature.     

Über die Umsetzung von Adipinsäurediamid mit Phosphorpentachlorid

Reaction of Adipic Acid Diamide with Phosphorus Pentachloride The reaction of adipamide (I) with phosphorus pentachloride in a solvent leads to (Cl₃P?NCCl₂CCl₂CH₂)₂ (II). The stages of the reaction are: 1. chlorination of the keto and methylen groups 2. formation of the ? N?PCl₃ group. This result is a supplement of the existing conception about the course of the reaction of carboxylic acid amides with phosphorus pentachloride. The reaction of (I) with PCl₅ without any solvent has been reproduced and the course of reaction has also been investigated. This reaction gives mainly NC(CH₂)₄CN. The resulting product of a careful hydrolysis of (II) is (Cl₂OPN?CClCl₂CH₂)₂. A total hydrolysis gives back (I).     

A study of the atmospherically relevant reaction between molecular chlorine and dimethylsulfide (DMS): Establishing the reaction intermediate and measurement of absolute photoionization cross-sections

In a study using UV photoelectron spectroscopy (PES) of the atmospherically relevant reaction

CH₃SCH₃ + Cl₂ → CH₃SCH₂Cl + HCl

Kinetics and mechanisms of oxidation of 1-octene and heptanal by crown ether-solubilized potassium permanganate in non-aqueous solvents

The kinetics of oxidation of 1-octene and heptanal by 18-crown-6-ether-solubilized KMnO₄ in benzene and CH₂Cl₂ have been investigated. In benzene, the oxidation of 1-octene is first order with respect to the oxidant and zero order with respect to the substrate, whereas in CH₂Cl₂ the reaction is first order with respect to both substrate and oxidant. The reaction of heptanal followed different kinetics being first order with respect to both substrate and oxidant, regardless of whether benzene or CH₂Cl₂ was employed as the solvent. The values of activation energy E _a, standard enthalpy H ^*, standard entropy change S ^*, and standard free energy G ^*, for the reaction, are reported. Mechanistic pathways for the studied reactions are also proposed.     

Pivotal Role of Holes in Photocatalytic CO2 Reduction on TiO2

Evidence is provided that in a gas-solid photocatalytic reaction the removal of photogenerated holes from a titania (TiO₂) photocatalyst is always detrimental for photocatalytic CO₂ reduction. The coupling of the reaction to a sacrificial oxidation reaction hinders or entirely prohibits the formation of CH₄ as a reduction product. This agrees with earlier work in which the detrimental effect of oxygen-evolving cocatalysts was demonstrated. Photocatalytic alcohol oxidation or even overall water splitting proceeds in these reaction systems, but carbon-containing products from CO₂ reduction are no longer observed. H₂ addition is also detrimental, either because it scavenges holes or because it is not an efficient proton donor on TiO₂. The results are discussed in light of previously suggested reaction mechanisms for photocatalytic CO₂ reduction. The formation of CH₄ from CO₂ is likely not a linear sequence of reduction steps but includes oxidative elementary steps. Furthermore, new hypotheses on the origin of the required protons are suggested.     

New development of Meyers’ methodology: stereoselective preparation of an axially chiral 5,7-fused bicyclic lactam related to circumdatins/benzomalvins and asperlicins

The stereoselective preparation of a new Meyers’ bicyclic lactam-bridged biaryl 1, highly structurally related to circumdatins, benzomalvins and asperlicins, is reported. Using the popular Meyers’ diastereoselective lactamization, under dehydrating conditions (CH₂Cl₂/reflux/MgSO₄), trans-(aS,R,S)-1 was obtained in a rather modest yield of 25% and an excellent diastereoselectivity >95%. An alternative procedure making use of the activating agents of carboxylic acid (Mukaiyama reagent and FEP) allowed the lactamization process to take place under milder conditions (CH₂Cl₂/20 °C) affording trans-(aS,R,S)-1 in fairly good yields (50%–85%) and in up to 65% de.     

Syntheses and Structures of S4N4(OCH3)2 and CH3OS4N4(O)Cl

The reaction of S₄N₄Cl₂ with CH₃OH gives S₄N₄(OCH₃)₂, a simple dimethoxoderivative of S₄N₄. Its overall geometry is analogous to other compounds of the S₄N₄X₂ type. The chlorination of S₄N₄(OCH₃)₂ leads to the oxidation of one sulfur atom to S^VI and CH₃OS₄N₄(O)Cl is formed. The compounds were characterized by ir spectroscopy and their crystal structures were determined from single crystal diffraction data collected at ?153°C. The presence of S^VI in the molecule of CH₃OS₄N₄(O)Cl is manifested by a marked shortening of the bonds formed by this atom as compared with S₄N₄Cl₂ and S₄N₄(OCH₃)₂.     

A kinetic investigation of reaction of [Os(N)(CH2SiMe3)4][NBun4] with methyl iodide

A high oxidation state alkylnitridoosmium complex, [Os(N)(CH₂SiMe₃)₄][NBuⁿ₄] acts as a nucleophile in reactions with alkyl halides. Alkylimido complexes, Os(NR)(CH₂SiMe₃)₄, are produced. The reaction between [Os(N)(CH₂SiMe₃)₄]⁻ [NBuⁿ₄] and MeI is second order with k₂= 9.5 x 10⁻⁵ sec^t̄1 M⁻¹ at 23°C in CD₂Cl₂ under pseudo first order conditions. The entropy of activation, ΔS^≠, was found to be −10.6 ± 0.5 cal M⁻¹ K⁻¹ and the enthalpy of activation, ΔH^≠, was found to be 19.6 ± 0.2 kcal M⁻¹. The reaction proceeds faster in polar, non-coordinating solvents than in either non-polar solvents or in solvents which can coordinate to the osmium center.     

Investigation of molecular order in liquid-crystalline solutions of cellulose triacetate using PMR spectroscopy

Liquid-crystalline solutions of cellulose triacetate (CTA) in trifluoroacetic acid (TFA)–CH₂Cl₂, TFA–1.2-dichloroethane (1,2-DCE) solvent mixtures were examined by means of PMR spectroscopy. CTA forms both cholesteric and nematic phases in these solvents depending on the CTA concentration. In cholesteric solutions the CH₂Cl₂ signal is initially a singlet and then splits into a doublet. The time dependence of the splitting and the effect of CTA concentration are reported. The results suggest that the cholesteric phase slowly changes into a nematic phase in the magnetic field. The splitting of the CH₂Cl₂ proton signal into a doublet and the 1,2-DCE signal into a quartet are due to direct magnetic dipole-dipole interactions. Rotation of the sample in the magnetic field results in the disappearance of the doublet or quartet and suggests that the solvent molecules are originally oriented in the direction of the magnetic field. In the biphasic region, immediate splitting of the CH₂Cl₂ proton signal suggests that the anisotropic phase is nematic.     

Synthese und Kristallstruktur von (PPh4)2[Mo2(S2)2Cl8] · 2 CH3CN und seine topotaktische Umwandlung zu (PPh4)2[Mo2(S2)2Cl8]

Synthesis and Crystal Structure of (PPh₄)₂[Mo₂(S₂)₂Cl₈] · 2 CH₃CN and its Topotactic Transformation to (PPh₄)₂[Mo₂(S₂)₂Cl₈] MoS₂Cl₃ was prepared from molybdenum and S₂Cl₂ at 200 °C. Its reaction with PPh₄Cl in acetonitrile yielded (PPh₄)₂[Mo₂(S₂)₂Cl₈] · 2 CH₃CN. In vacuum or upon warming, it loses the acetronitrile without degradation of the crystals. According to the X-ray crystal structure determinations both compounds, with and without acetonitrile, are triclinic. They contain the same [Cl₄Mo(μ-S₂)₂MoCl₄]^2– ions, in which the Mo atoms are joined by two disulfido groups and an Mo–Mo bond. Details of the crystal packings and their topotactic transformation are given.