An efficient method for the preparation of alkylidenecyclopropanes

Yields obtained from Wittig reactions with cyclopropylidenetriphenylphosphorane are greatly improved by addition of the phase-transfer catalyst, TDA-1.     

An efficient method for the preparation of N-phosphinoyl and N-sulphonyl imines directly from aromatic aldehydes

Reaction of phosphinamides and sulphonamides with aromatic aldehydes at 0°C in the presence of titanium tetrachloride and triethylamine provides a simple one-step preparation of N-phosphinoyl and N-sulphonyl imines.     

An efficient method for computing excess free energy of liquid

We present a new theoretical method for efficient calculation of free energy of liquid. This interaction entropy method allows one to compute entropy and free energy of liquid from standard single step MD (molecular dynamics) simulation directly in liquid state without the need to perform MD simulations at many intermediate states as required in thermodynamic integration or free energy perturbation methods. In this new approach, one only needs to evaluate the interaction energy of a single (fixed) liquid molecule with the rest of liquid molecules as a function of time from a standard MD simulation of liquid and the fluctuation of distribution of this interaction energy is then used to calculate the interaction entropy of the liquid. Explicit theoretical derivation of this interaction entropy approach is provided and numerical calculations for the benchmark liquid water system were carried out using three different water models. Numerical analysis of the result was performed and comparison of the computational result with experimental data and other theoretical results were provided. Excellent agreement of calculated free energies with the experimental data using TIP4P model is obtained for liquid water.     

An efficient method for the synthesis of 1-chlorophenazines based on the selective cathodic reduction of 3,3,6,6-tetrachloro-1,2-cyclohexanedione

An efficient method for the synthesis of 1-chlorophenazines has been established. It is based on the use of 3,6,6-trichloro-2-hydroxy-2-cyclohexen-1-one 4 as a synthetic equivalent of 3-chloro-1,2-benzoquinone 3. The intermediate 4 was prepared in near quantitative yield by electroreductive monodechlorination of 3,3,6,6-tetrachloro-1,2-cyclohexanedione 1, which is an inexpensive and easily available starting material. Efficient reactions of 4 with primary 1,2-phenylenediamines provided the corresponding 1,1,4-trichloro-1,2,3,4-tetrahydrophenazines 6, which were directly aromatized by treatment with 2,6-lutidine to give the title compounds in high yields. X-ray crystallographic structures for 1,1,4-trichloro-1,2,3,4-tetrahydro-6-methylphenazine 6f, 8-benzoyl-1,1,4-trichloro-1,2,3,4-tetrahydro-phenazine 6ea, and 1,7-dichlorophenazine 10db have been determined.     

An efficient enzymatic preparation of rhinovirus protease inhibitor intermediates

The development of an efficient route for the preparation of (2S)-2-[3-{[(5-methylisoxazol-3-yl)carbonyl]amino}-2-oxopyridin-1(2H)-yl]pent-4-ynoic acid (4), a key intermediate in the synthesis of a human rhinovirus (HRV) protease inhibitor, is presented. In the presence of 40% acetonitrile, the alkaline protease from Bacillus lentus can catalyze the kinetic resolution of racemic ester 7 to afford (S)-acid 4 in 49% chemical yield/per cycle with 98% ee and >98% HPLC purity. The (R)-ester can then be readily recycled via a DBU catalyzed epimerization. The enzymatic preparation described here is superior to the existing chemical resolution route, exhibiting lower costs as well as higher yields, enantioselectivity, and substrate loads. In addition, this protease displays broad substrate specificity toward this class of compounds and can be easily extended to the preparation of other tripeptide mimetics of rhinovirus protease inhibitors.     

An efficient and simple method for the preparation of symmetrical disiloxanes from hydrosilanes by Lewis acid-catalyzed air oxidation

Symmetrical disiloxanes were prepared in high yields by air oxidation of mono, di, and trihydrosilanes under Lewis acid catalysis.     

An efficient method for the calculation of quantum mechanics/molecular mechanics free energies

The combination of quantum mechanics (QM) with molecular mechanics (MM) offers a route to improved accuracy in the study of biological systems, and there is now significant research effort being spent to develop QM/MM methods that can be applied to the calculation of relative free energies. Currently, the computational expense of the QM part of the calculation means that there is no single method that achieves both efficiency and rigor; either the QM/MM free energy method is rigorous and computationally expensive, or the method introduces efficiency-led assumptions that can lead to errors in the result, or a lack of generality of application. In this paper we demonstrate a combined approach to form a single, efficient, and, in principle, exact QM/MM free energy method. We demonstrate the application of this method by using it to explore the difference in hydration of water and methane. We demonstrate that it is possible to calculate highly converged QM/MM relative free energies at the MP2/aug-cc-pVDZ/OPLS level within just two days of computation, using commodity processors, and show how the method allows consistent, high-quality sampling of complex solvent configurational change, both when perturbing hydrophilic water into hydrophobic methane, and also when moving from a MM Hamiltonian to a QM/MM Hamiltonian. The results demonstrate the validity and power of this methodology, and raise important questions regarding the compatibility of MM and QM/MM forcefields, and offer a potential route to improved compatibility.     

ortho-Alkynylphenyl thioglycosides as a new type of glycosylation donors under the catalysis of Au(I) complexes

ortho-Alkynylphenyl thioglycosides, prepared readily via Sonagashira coupling of ortho-bromophenyl thioglycosides with alkynes, could undergo glycosidation effectively under the catalysis of a gold(I) complex.     

An efficient procedure for preparation of 2-monoalkyl or 2-monoaryl-3-ethoxycyclobutanones

Optimized reaction conditions for the preparation of various 2-monosubstituted 3-ethoxycyclobutanones are described. 2-Monoalkyl 3-ethoxycyclobutanones were efficiently prepared by the reaction of the corresponding carboxylic acid chlorides and an excess amount of ethyl vinyl ether in the presence of diisopropylethylamine at 90 °C in a sealed tube. 2-Monoaryl 3-ethoxycyclobutanones were prepared by using 2,6-lutidine as a base in the above-mentioned procedure.     

A one-step procedure for facile, selective synthesis of protected d-glucopyranosides with free 2-C hydroxyl group starting from peracetylated β-D-glucopyranose

An important field in carbohydrate chemistry is to look for regioselective re-actions of saccharides to simplify the chemical synthesis of oligosaccharides. Oneof such efforts nowadays is directed to the convenient preparation of protected D-     

Facile and efficient method for preparation of schiff bases catalyzed by P2O5/SiO2 under free solvent conditions

A simple and convenient method for the preparation of Schiff bases is developed. In this method, the Schiff base compounds were prepared from the reaction of carbonyl compounds with primary amines. In this reaction, P₂O₅/SiO₂ have catalyzed the Schiff base formation in dry media under solvent‐free conditions. Advantages of this method are use of an inexpensive and efficient catalyst, high yields of products, short reaction times, and simpli‐city of the reaction and workup. © 2008 Wiley Periodicals, Inc. Heteroatom Chem 19:43–47, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20383     

4-Hydroxy-2-quinolones 127. Simple method for exchanging chlorine for hydroxyl in 1-R-4-chloro-3-ethoxycarbonyl-2-oxo-1,2-dihydroquinolines

Treatment of ethyl 1-R-4-chloro-2-oxo-1,2-dihydroquinoline-3-carboxylates with sodium nitrite in DMSO is a convenient method for their conversion to the corresponding 4-hydroxy derivatives. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1359–1364, September, 2007.     

An efficient method for the preparation of tertiary esters by palladium-catalyzed alkoxycarbonylation of aryl bromides

The palladium-catalyzed alkoxycarbonylation of aryl bromides is described for the efficient preparation of tertiary esters. The protocol proved compatible with a wide variety of functionalized (hetero)aromatic bromides, as well as several different sterically hindered tertiary alcohols, affording the alkoxycarbonylated products in high yields. Finally, the formation of aromatic trityl esters is discussed.     

A new method for inversion of hydroxyl group of carbocyclic nucleosides

The hydroxyl group of carbocyclic nucleosides was inversed when the compounds were treated with Me_3SiCl,KCN and a catalytic amount of NaI in DMF/CH_3CN.     

An efficient and convenient method for preparation of disulfides from thiols using air as oxidant catalyzed by Co-Salophen

Disulfides have been synthesized by oxidation of thiols using air as oxidant catalyzed by Co-Salophen with high yields,mild and neutral conditions,and easy procedures of the catalyst.The products were confirmed by ~1H NMR and IR.