The Structures and Stability of HNOS Isomers

Potential energy surface of HNOS system is investigated by means of MP2 method with 6-311 G(d,p) basis set.The energy for each minimum and saddle point on the potential energy surface is corrected at the QCISD(T)/6-311 G(3df,2p) level of theory with zero-point vibrational energy included.As a result ,eighteen isomers are theoretically predicted and cis-HNSO is found to be global minimum on the potential energy surface,Wherein,fourteen isomers are considered as kinetically stable species,and should be experimentally observed.Comparisons are made for HNOS system with its analogues,HNO2 and NHS2.The nature of bonding and isomers‘ stability of HNOS system are similar to HNS2.The obvious similarities and discrepancies among HNOS,HNO2 and HNS2 are attributed to the hypervalent capacity of sulfur,oxygen and nitrogen atoms.     

Synthesis of Chiral 2,5—Bis（oxazolinyl） thiophenes and Their Application as Chiral Shift Reagents for 1,1′—Bi—2—naphthol

A series of C2-symmetrical chiral 2,5-bis (4′-alkyloxazolin-2-yl) thiophenes (thiobox) have been synthesized from thiophene-2,5-dicarboxylic acid by sequential amidation with a chiral ethanolamine,conversion of hydroxyl to chloro group, and base-promoted oxazoline ring formation.As demonstrated by (-)-2,5-bis[4′-(S)-isopropyloxazolin-2′-yl] thiophene,these thiobox systems exhibited remarkable chirality recognition of 1,1′-bi-2-naphthol giving rise to pronounced shifts in the ^1H NMR signals of the latter axial chiral compound at the positions of C-3,C-4,C-5,and C-8.     

Enantio- and Diastereoselective Oxidation of N-Alkylimines Using Chiral α-Bromonitriles and Hydrogen Peroxide System

Chiral α-bromonitriles were prepared with good chemical and optical yields starting from natural α-amino acids by dehydrating the corresponding α-bromoamides with thionyl chloride. The combined system α-bromonitriles/hydrogen peroxide was examined for the enantio- and diastereoselective oxidation of N-alkylimines in basic media at room temperature. The oxidation of N-tertiobutylarylimines leads to optically active oxaziridines with moderate enantiomeric excess. However, the oxidation of (S)-1-phenylethylarylimines affords the corresponding oxaziridines with good diasteromeric excess up to 97/3 as proved by gaseous-phase chromatography.     

The Deuterated “Magic Methyl” Group: A Guide to Site-Selective Trideuteromethyl Incorporation and Labeling by Using CD3 Reagents

In the field of medicinal chemistry, the precise installation of a trideuteromethyl group is gaining ever-increasing attention. Site-selective incorporation of the deuterated “magic methyl” group can provide profound pharmacological benefits and can be considered an important tool for drug optimization and development. This review provides a structured overview, according to trideuteromethylation reagent, of currently established methods for site-selective trideuteromethylation of carbon atoms. In addition to CD₃, the selective introduction of CD₂H and CDH₂ groups is also considered. For all methods, the corresponding mechanism and scope are discussed whenever reported. As such, this review can be a starting point for synthetic chemists to further advance trideuteromethylation methodologies. At the same time, this review aims to be a guide for medicinal chemists, offering them the available C−CD₃ formation strategies for the preparation of new or modified drugs.     

Synthesis and Catalytic Application of Chiral 1, l＇-Binaphthyl Polymers

The synthesis of a new type of polymers with main chain chirality based on BINOL skeleton is described. Titanium-BINOLate catalysts are easily generated from these polymers and applied to the asymmetric reaction of Et2Zn with benzaldehyde. The products are obtained in good yields with moderate enantioselectivities.     

Stereoselective Addition of Organotitanium and Grignard Reagents to 3,5-O-isopropylidene-L-glucurono-γ-lactone

HowiinolA1',anovellactoneisolatedfromtheethanolicextractsoftherootandstembarkofGoniothamushowiiMerr.(Annonaceae)inourlaboratory,possessessignificantantitumoractivitiesinvitroandinvivowithlowtoxicity.Recently,wehavesynthesized1andits7a-isomer(7-epi-howiinolA)startingfromcommerciallyavailableD-glycer-D-guIo-hepicno-Y-Iactone,but7-epi-howiinoIAhaslesscytotoxicactivitiesinvitrothanI.3'5Inordertoincreasetheyieldof76-isonertargetcompoundsandtoprovidemoresamplesforthestudyontherelationshipofstrU…     

The First Rotational Isomers of Stable Selenobenzaldehydes and their η1-Tungsten Complexes

The first rotational isomers of stable selenoaldehydes are synthesized by deselenation of cyclic polyselenides having an efficient steric protection group, 2, 4, 6-tris[bis(trimetylsilyl)methyl]phenyl (Tbt). Reactions of these selenoaldehydes with W(CO)₅.THF gives the corresponding η¹-selenoaldehyde tungsten complexes, the structures of which are established by X-ray crystallography.     

Synthesis of Chiral N-Ferrocenylmethylaminoalcohols and their Application in Enantioselective Addition of Diethylzinc to Aldehydes

Three chiral N-ferrocenylmethylaminoalcohols were synthesized from readily available natural L-valine, leucine and phenylanine, and used as chiral ligands in the enantioselective addition of diethylzinc to aldehydes.     

Synthesis and Properties of Chiral Molecular Clefts Related to Tröger's Base

The chiral cavities present in 2,3:6,7-dibenzo-9-oxabicyclonona-2,6-diene, dibenzobicyclo[b,f][3.3.1]nona-5a, 6a-diene-6,12-dione, bicyclo[3.3.1]nonane and dibenzobicyclo[b,f],diazocines are reminiscent of Tröger's base, which has been widely used as a molecular cleft in supramolecular chemistry. The synthetic methodology to provide key derivatives for elaboration into new supramolecular structures, efficient resolution methods, the introduction of additional recognition groups and applications in supramolecular chemistry of these structurally related molecular clefts are reviewed.     

Enantiomeric Separation of Epinephrine and Salbutamol by Micellar Electrokinetic Chromatography Using β-Cyclodextrin as Chiral Additive

Introduction The development of chiral substances, especially inthe pharmaceutical field, places increasing demands onanalytical methods for the separation of these kinds ofisomers and the chiral purity control of drugs in phar-macokinetic studies. As the enantiomers of epinephrineand salbutamol have different pharmacological andtoxicological characteristics, separation and quantitationof the single enantiomers are required. Analytical methods used so far for the enantiomerseparation inclu…     

Enantiomeric Separation of Epinephrine and Salbutamol by Micellar Electrokinetic Chromatography Using β-Cyclodextrin as Chiral Additive

Enantiomeric separation of epinephrine and salbutamol was investigated by micellar electrokinetic chromatography employing β-cyclodextrin as chiral additive in ammonium chloride-ammonia solution. The analytes were detected by electrochemistry using gold microelectrode at 0.65 V versus SCE reference electrode. The effects of detection potential,concentration of β-cyclodextrin, concentration of sodium dodecyl sulfate, pH value of electrolyte and applied voltage were discussed.     

The Paramagnetic 2D Chiral—porous Polymer of L—Phenylalanine and Manganese

1 INTRODUCTION Assemblies of chiral and helical structures are common in biology. Molecular materials with chiral porous structures and helical morphology have attracted a great deal of attention in multidiscipli- nary areas such as zeolite-like coordination poly- mers, biomaterials, and chiral chemistry[1～3]. The intensive interest in these materials arises, to a large extent, from their interesting properties and poten- tials in various applications such as electrical con- ductivity, …     

The Optical Resolution of Chiral Tetrahedrone-type Clusters Contai- ning SCoFeM (M=Mo or W) Using High Performance Liquid Chromatography Chiral Stationary Phase

Optical resolution using high performance liquid chromatography chiral stationary phases has been widely used in many modern research fields such as asymmetric synthesis, asymmetric catalytic and separation of racemic pharmaceuticals. In the past years, various chiral stationary phases have been developed and have been commercially available1. Among them, polysaccharide based phases are the widely used CSPs. A wide variety of enantiomeric compounds including chiral aromatic alcohols, enant…     

Enantioseparation of Tropic Acid and Its Esters by CEKC Using Sulfated β-Cyclodextrin as a Chiral Selector

Capillary electrokinetic chromatography was successfully applied to the enantioseparation of tropic acid and its four alkyl esters (methyl, ethyl, propyl and butyl), with the same chiral center, Separation was with sulfated β-cyclodextrin (4%, m/v) containing 20 mM phosphate buffer at pH 3.0 as background electrolyte at 20 °C. The results showed that, besides hydrogen-bonding interactions between these compounds with sulfated β-CD, for tropic acid and its methyl ester the steric hindrance effect was also an important factor. However, for the other esters (ethyl, propyl and butyl), the hydrophobicity effect was higher.     

The Numbers of Configurations, Chiral and Achiral Configurations of Saturated Polybasic Alcohols Containing an Adamantane Skeleton

By using Polya' s theorem, the generating functions of configurations, chiral and achi-ral configurations of saturated polybasic alcohols containing an adamantane skeleton were obtained. Tn order to calculate the generating functions of compounds which are substituted with a limited condition, an exclusive method is used and cycle index is modified.     

Synthesis of Chiral Aminophenols Based on Proline and Their Application in Enantioselective Addition of Diethylzinc to Aldehydes

Three 2-{（3R, 7aS )-1, 1-disubstituted-tetrahydro-lH-pyrrolo [ 1,2- c ] [ 1,3 ] oxazol-3-yl} phenols have been synthesized from salicylaldehyde and amino alcohols derived from L-proline, and used as ligands in enantioselective addition of diethylzinc to aldehydes, the ee values of obtained secondary alcohols were found in the range of 0-90%.     

Enantioselective Synthesis of (E)-δ-Boryl-Substituted anti-Homoallylic Alcohols Using Palladium and a Chiral Phosphoric Acid

(E)-δ-Boryl-substituted anti-homoallylic alcohols are synthesized in a highly diastereo- and enantioselective manner from 1,1-di(boryl)alk-3-enes and aldehydes. Mechanistically, the reaction consists of 1) palladium-catalyzed double-bond transposition of the 1,1-di(boryl)alk-3-enes to 1,1-di(boryl)alk-2-enes, 2) chiral phosphoric acid catalyzed allylation of aldehydes, and 3) palladium-catalyzed geometrical isomerization from the Z to E isomer. As a result, the configurations of two chiral centers and one double bond are all controlled with high selectivity in a single reaction vessel.     

γ‐PCC and γ‐PCC‐SiO2 as Efficient Reagents for Oxidation of Thiols to Disulfides

Abstract

Oxidative coupling of thiols to the corresponding symmetrical disulfides was performed in the presence of γ‐picolinium chlorochromate and its silica gel supported. The reactivity of silica gel supported γ‐picolinium chlorochromate for thiophenol derivatives is more than the reactivity of pyridinium and γ‐picolinium chlorochromates.     

An Efficient Method for Catalytic Asymmetric Reduction of Diketones and Application of Synthesis to Chiral 2,5- Diphenylpyrrolidine and 2,5-Diphenylthiolane

Asymmetric reduction of diketones with borane reagents generated in situ using cheap and available NaBH_4 andSnCl_2 in the presence of(S)-(-)-α,α-diphenyl-2-pyrrolidinemethanol was successfully achieved to yield the corre-sponding chiral diols with excellent stereoselectivity and enantioselectivity.And the chiral diol was transformedinto optically pure C_2-symmetricl chiral amine or thioether.