Chemoenzymatic synthesis of enantiomerically pure terminal 1,2-diols

A new practical method for the enzymatic synthesis of 1,2-diols has been developed by employing a lipase catalyzed one-pot transesterification protocol. A series of substituted -acetoxyphenylethanones 3a–g have been reduced to the corresponding alcohols under mild conditions employing sodium borohydride and moist neutral alumina, and further subjected for lipase catalyzed irreversible transesterification in the same pot to give mono- and diacetate diols (R)-4 and (S)-5, which on hydrolysis afforded terminal 1,2-diols, (R)- and (S)-6 in high enantiomeric excess.     

Vanadium-catalyzed selective aerobic alcohol oxidation in ionic liquid [bmim]PF6

A selective aerobic oxidation of alcohols into the corresponding aldehydes or ketones was developed by using two-component system VO(acac)₂/DABCO in the ionic liquid [bmim]PF₆, and the catalysts can be recycled and reused for three runs without any significant loss of catalytic activity.     

Hydrogen substitution effect on the solubility of perhalogenated compounds in ionic liquid [bmim][PF6]

Solubility behaviors of binary mixtures of CFCl₃ (R-11), CFCl₂-CF₂Cl (R-113), CHCl₃ (R-20), CDCl₃ (R-20-d), CHCl₂–CF₃ (R-123) with room-temperature ionic liquid [bmim][PF₆] (1-butyl-3-methylimidazolium hexafluorophosphate) have been investigated using the volumetric and cloud-point methods, since all the systems show liquid–liquid equilibria (LLE). Large immiscibility (LLE) gaps of the perhalogenated compounds (R-11 and R-113) in the ionic liquid have been drastically reduced by the addition of only one hydrogen (or deuterium) in these compounds. The R-123 + [bmim][PF₆] binary system belongs to the Type-V fluid behavior. Noticeably large negative values (−2 to −8 cm³ mol⁻¹) of the excess molar volume in the ionic liquid-rich side solution have been observed for all the present systems. Experimental LLE data have been well correlated by the use of the NRTL (non-random two liquid) activity coefficient model.     

Solvent relaxation of a room-temperature ionic liquid [bmim][PF6] confined in a ternary microemulsion

In this paper we have reported the solvent and rotational relaxation of 1-butyl-3-methyl-imidazolium hexafluorophosphate ([bmim][PF₆]) confined in tween 20/([bmim][PF₆]/water microemulsion using coumarin 153 (C-153) as probe. The most interesting feature of our experiment was that we observed an increase in solvent relaxation time with increase in R (R = tween 20-to-[bmim][PF₆] molar ratio). This is due to the fact that with increase in [bmim][PF₆] content of the microemulsions, the microviscosity of the pool of the microemulsions increases, and motion of ions of [bmim][PF₆] is hindered in the pool of microemulsions. Since motion of ions is responsible for solvation in room-temperature ionic liquids (RTILs), solvent-relaxation time increases with increase in R.     

Influencing the regioselectivity of lipase-catalyzed hydrolysis with [bmim]PF6

An easy preparation of mono-deprotected thioglucopyranosides via a selective Candica cylindracea lipase-catalyzed hydrolysis of a commercially available peracetylated precursor is described. Especially, ethyl 2,3,4-tri-O-acetyl-1-thio-β-d-glucopyranoside and ethyl 2,3,6-tri-O-acetyl-1-thio-β-d-glucopyranoside were obtained in 100% and 54% isolated yields, respectively. The influence of the ratio of [bmim]PF₆/buffer toward the regioselectivity of the deacetylation step and the acyl migration is discussed.     

Microwave-assisted clean synthesis of 6-aryl-2,4-diamino-1,3,5-triazines in [bmim][PF6]

An efficient and green approach was developed to prepare 6-aryl-2,4-diamino-1,3,5-triazines from corresponding arylnitriles and dicyanodiamide in ionic liquid [bmim][PF₆] under computer-controlled microwave irradiation. Particularly valuable features of this method included the short reaction time, good yield, convenient operation and eco-friendly solvent.     

TEMPO-catalyzed oxidation of benzylic alcohols to aldehydes with the H2O2/HBr/ionic liquid [bmim]PF6 system

A selective oxidation of benzylic alcohols to the corresponding aldehydes in room temperature ionic liquid was achieved by using TEMPO/HBr/H₂O₂ system, and both ether-insoluble acetamido-TEMPO and ionic liquid [bmim]PF₆ can be successfully recovered and reused for the oxidation of the same (different) substrate.     

Surface of room temperature ionic liquid [bmim][PF6] studied by polarization- and experimental configuration-dependent sum frequency generation vibrational spectroscopy

Understanding and control of the surface properties such as molecular orientations are of great importance in numerous applications of ionic liquids. However, there remain discrepancies among the previous experimental and theoretical studies on the surface orientation and structures of room temperature ionic liquids(RTIL) systems. In this article, the orientation of 1-butyl-3-methylimidazolium([bmin]) cation at the air/liquid interface of a characteristic RTIL, 1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]), was investigated by the sum frequency generation vibrational spectroscopy(SFG-VS). Detailed polarization and experimental configuration analyses of the SFG-VS spectra showed the possibility of a small spectral splitting in the CH3 symmetric stretching region, which can be further attributed to the probable existence of multiple orientations for the interfacial [bmim] cations. In addition, the(N)–CH3 vibrations were absent, ruling out the prediction by several recent molecular dynamics simulations which state that portions of the [bmim] cations orient with a standing-up(N)–CH3 group at the ionic liquid surface. Hence, new realistic theoretical models have to be developed to reflect the complex nature of the ionic liquid surface.     

离子液体[bmim]PTSA的微波合成

近年来,随着绿色化学的兴起,离子液体作为一种新型的绿色溶剂已成为国内外科研工作者的研究热点之一.离子液体是由有机阳离子和无机阴离子组成的盐,可以根据需要控制阴阳离子的组成和结构,设计合成出不同特性的离子液体[1].     

Selective alkylation of phenol with tert-butyl alcohol catalyzed by [bmim]PF6

Alkylation of phenol with tert-butyl alcohol (TBA) in a room temperature ionic liquid, 1-butyl-3-methylimidazoliumhexafluorophosphate ([bmim]PF₆), has been investigated. The effects of various parameters such as reaction temperature, reaction time, reactant ratio (mol ratio of phenol to that of TBA), and the amount of the ionic liquid used were studied. The [bmim]PF₆ ionic liquid was found to catalyze the reaction with high conversion and good selectivity.     

A novel and green synthesis of kojic acid derivatives in ionic liquid [bmim]BF4

A series of 3-(3-hydroxy-6-methyl-4-oxo-4H-pyran-2-yl)-3-phenylpropanamide derivatives were synthesized efficiently by one-pot condensation of aromatic aldehydes, meldrum’s acid, allomaltol, and ammonium acetate in ionic liquid [bmim]BF₄. The novel synthesis method offers the advantage of operational simplicity, mild reaction conditions, short reaction time, higher yields, and environmental friendliness.     

Synthesis of tetrahydro-β-carbolinediketopiperazines in [bdmim][PF6] ionic liquid accelerated by controlled microwave heating

Because of their negligible vapor pressures and large dipoles, ionic liquids are excellent media for microwave-accelerated organic reactions. Using low-power microwave irradiation in the new [bdmim][PF₆] ionic liquid with temperature controlled at 60 °C, a three-step synthesis (Pictet-Spengler, Schotten-Baumann, and intramolecular ester amidation) of tetrahydro-β-carbolinediketopiperazines starting from tryptophan methyl ester was achieved with good isolated yields (49-69%) in only 5 min.     

Mild synthesis of enantiomerically pure imidazo-[1,2-a]azepines mediated by Yb(OTf)3

The reaction of various chiral 2,2′-diaryldialdehydes with achiral and chiral 1,2-diamines in the presence of Lewis acids to give imidazo[1,2-a]azepines was investigated. Best results were achieved with Yb(OTf)₃; the reaction outcome is strongly dependent upon the geometric features of both reactants. Kinetic resolution of rac-2,2′-dinaphthyldialdehyde with (R,R)-1,2-diphenyl-1,2-diamminoethane (up to 92% e.e.) was achieved.     

Chemoenzymatic synthesis of glycosylated enantiomerically pure 4-pentene 1,2- and 1,3-diol derivatives

1-Dimethylthexylsiloxy-2-chloroacetoxy-4-pentene 2 and 1-dimethylthexylsiloxy-3-chloroacetoxy-4-pentene 3 were saponified with Pseudomonas lipase to give (R)-1-dimethylthexylsiloxy-4-pentene-2-ol (ee=99%) and (S)-2 (ee=99%) and (S)-1-dimethylthexylsiloxy-4-pentene-3-ol (ee=99%) and (R)-3 (ee=98%), respectively. All enantiomers were chemically transformed into the corresponding enatiomerically pure 2-benzoyloxy-4-pentene-1-ols 8 and 3-benzoyloxy-4-pentene-1-ols 14, respectively. Mannosylation of (R)-8 and (S)-14 with 2,3,4,6-tetra-O-benzoyl-a-d-mannopyranosyl trichloroacetimidate afforded the corresponding mannopyranosides.     

An efficient one pot method for synthesis of carboxylic acids from nitriles using recyclable ionic liquid [bmim]HSO4

Environmentally benign ionic liquid [bmim]HSO₄ was found suitable for conversion of nitriles into carboxylic acids under mild conditions with excellent purity.     

Efficient, green and regioselective synthesis of 1,4,5-trisubstituted-1,2,3-triazoles in ionic liquid [bmim]BF4 and in task-specific basic ionic liquid [bmim]OH

Convenient and environmentally benign procedures have been reported for the synthesis of 1,4,5-trisubstituted-1,2,3-triazoles by the reaction of aryl azides with active methylene compounds in ionic liquid [bmim]BF₄ in the presence of l-proline as a catalyst and also in task-specific basic ionic liquid [bmim]OH. The methodologies defined herein avoid the severe conditions as posed by earlier existing methods and proved to be efficient in terms of good yields, operational simplicity, easy workup and short reaction time.     

[Bmim]PF6 and BF4 ionic liquids as novel and recyclable reaction media for aromatic amination

Activated aryl halides undergo smooth nucleophilic substitution reactions with secondary amines in 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) or 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF₄) ionic liquids (ILs) at room temperature to afford the corresponding arylamines in excellent yields under mild and neutral conditions.     

Nonaqueous microemulsion-containing ionic liquid [bmim][PF6] as polar microenvironment

The phase behavior of toluene/Triton X-100 (TX-100)/1-butyl-3-methylimidazolium hexafluorophosphate([bmim][PF6]) was studied. It was demonstrated that the single-phase microemulsion area covered about 75% of the phase diagram at 25 °C. Electrical conductivities of the system with different w ([bmim][PF6]-to-TX-100 molar ratio) values were determined, and the results were used to locate the sub-regions of the single-phase microemulsion. The results showed that a transform from [bmim][PF6]-in-oil ([bmim][PF6]/O) microstructure via a bicontinuous region to an oil-in-[bmim][PF6] (O/[bmim][PF6]) microstructure occurred with the increase of Φ (weight fraction of TX-100 and [bmim][PF6] in the system). The aggregate size of the reverse microemulsions of [bmim][PF6]/O was determined using small-angle X-ray scattering. The results showed that the size of the reverse microemulsions depended markedly on the w values.     

Measurement and correlation of vapor pressure of benzene and thiophene with [BMIM][PF6] and [BMIM][BF4] ionic liquids

An apparatus used to measure vapor pressure of organic solvents was set up, and vapor pressure of mixture of ionic liquids ([BMIM][PF₆] and [BMIM][BF₄]) and aromatic compounds (benzene and thiophene), with mole fraction of organic solute from 0.1 to 0.75 was measured by using saturation vapor pressure method at temperature from 303 K to 343 K. Then NRTL equation was used to correlate the experimental data. The overall average relative deviation of activity coefficients for the whole system is 2.30%, which indicates that NTRL equation can be utilized to correlate vapor pressure of binary systems containing ionic liquids. The results show that ionic liquids can depress the volatility of aromatic compounds.