Stable bis(2-chloro-2,2-difluoroethoxy)-fluoromethyl cation at room temperature

A stable carbocation was prepared by reacting bis(2-chloro-2,2-difluoroethyl) difluoroformal with SbF₅. The carbocation's structure was confirmed by ¹⁹F, ¹H and ¹³C NMR measurements. The carbocation is stable at room temperature for more than 2 weeks and was converted into the corresponding carbonate when reacted with water.     

Reaction of N‐(phenyl and methyl)‐C‐arylnitrones with DMAD in ionic liquid: Efficient synthesis of Δ4‐isoxazolines

Facile synthesis of N‐(methyl and phenyl)‐Δ⁴‐isoxazolines via the reaction of (Z)‐N‐(methyl and phenyl)‐C‐arylnitrones with dimethyl acethylenedicarboxylate, DMAD, in ionic liquid is described. (Z)‐N‐methyl‐C‐arylnitrones afforded the high yield of N‐methyl‐Δ⁴‐isoxazolines 4a , 4b , 4c , 4d , 4e in ionic liquid, [bmim]BF₄, at room temperature. However, the reaction of (Z)‐N‐phenyl‐C‐arylnitrones with DMAD afforded the mixtures of cis and trans isomers of related N‐phenyl‐Δ⁴‐isoxazolines ( 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j , 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j ) under these conditions. J. Heterocyclic Chem., (2012).     

Photoactivated 1,3-dipolar cycloaddition for the rapid preparation of F labelled radiotracers

An ¹⁸F-labelled 2,5-diaryl tetrazole reagent has been prepared and reacted with substituted alkene dipolarophiles through a photoactivated 1,3-dipolar cycloaddition reaction. The radiobioconjugation reaction furnished the desired product in 5 min with radiochemical conversions of 85-95% at room temperature. Remarkably, for the activated dipolarophiles, these results were obtained in highly dilute solutions (10-100 μM).     

Regioselective synthesis of quinolone-annulated sulfur heterocycles by aryl radical cyclization

The tin hydride-mediated cyclizations of a number of sulfides and sulfones under mild, neutral conditions, have been investigated accompanied by some amount of β-scission product for sulfides. The sulfides were derived from 4-mercaptoquinolone and 2-bromobenzyl bromides by phase transfer catalyzed reaction and the corresponding sulfones were prepared by treatment of the sulfides with m-CPBA at room temperature. The sulfides and the corresponding sulfones were then reacted with ⁿBu₃SnH-AIBN to give regioselective quinolone-annulated sulfur heterocycles.     

Syntheses and reactions of N‐perfluoroalkanesulfonylimino sulfurous dichlorides

Treatment of N,N‐dichloroperfluoroalkanesulfonylamines with sulfur powder at room temperature gave the title products R_fSO₂N=SCl₂ in good yields. They reacted readily with dimethyl sulfoxide, chloral, DMF, benzophenone, and similar compounds to form to corresponding imines R_fSO₂N=YR¹R² (Y: S, C). A reaction mechanism, one involving formation of a four‐membered intermediate, is proposed. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10: 41–48, 1999     

Acyclic nitronate olefin cycloaddition (ANOC): regio- and stereospecific synthesis of isoxazolines

We report the first demonstrations of intra- and intermolecular acyclic nitronate olefin cycloaddition (ANOC) reactions that enable the highly efficient syntheses of isoxazolines bearing various functional groups. This general approach to accessing γ-lactone fused isoxazolines was hitherto unprecedented. The room temperature transformations reported herein exhibit wide substrate scopes, as evidenced by more than 70 examples, including the generation of five tricyclic isoxazolines. The robustness of this methodology was confirmed by a series of trials that afforded highly functionalized isoxazolines. Both experimental results and density functional theory calculations indicate that these transformations proceed via the in situ formation of acyclic nitronates together with concerted [3+2] cycloaddition and tert-butyloxy group elimination processes to give regio- and stereospecificity.

A novel acyclic nitronate olefin cycloaddition (ANOC) reaction was successfully established, which enabled facile construction of various isoxazolines.     

Iron(II) Complexes of Chiral Tridentate Nitrogen Donors and their Application in Catalytic Hydrosilylation Reactions

Enantiomerically pure, C₂-symmetric 2,6-bis(pyrazol-3-yl) pyridine ligands were obtained by treatment of diethyl-2,6-pyridinedicarbonate with (1R,4R)-(+)-camphor in the presence of NaH followed by ring closure with hydrazine. After twofold N-alkylation at the pyrazole rings, the addition of iron(II) chloride led to the according pentacoordinate dichloridoiron(II) complexes. All intermediates of the ligand synthesis, the ligands bearing NCH₃ and NCH₂C₆H₅ groups and the derived iron(II) complexes were structurally characterized by means of X-ray structure analysis. In-situ reaction with iron(II) carboxylates resulted in the formation of iron(II) carboxylate complexes, which turned out to be highly active in the hydrosilylation of acetophenone. However, even at room temperature, the enantiomeric excess of the product 1-phenylethanol is poor. ⁵⁷Fe Mössbauer spectroscopy gave an insight into the species formed during catalysis.     

Thermal analytical and infrared spectroscopic investigations on polymorphic organic compounds—I

Seven polymorphic compounds are described, for each of which at least one enantiotropic relationship can be shown. 2-Chloro-ethylamine hydrochloride is a classical example, with two highly reproducible transformation points. Compounds which do not normally occur in their highest-melting form include 3,4-dibenzyloxyphenylacetic acid (3 modifications), 2-chlorotriethylamine hydrochloride (2 modifications) and 3,5-dimethoxbenzamide (3 modifications).N-Benzylphthal-imide and 2-chloro-4-nitrobenzoic acid occur naturally as mixtures of two modifications, the lower-melting of which is metastable at room temperature and the higher-melting is stable, with transformation points between 10 and 20° C. Only 2,4-dinitrophenyl-2,4-dinitrobenzoate (4 modifications) occurs naturally as the pure highest-melting modification, which is stable at room temperature.     

Strong deshielding in aromatic isoxazolines

Very strong proton deshielding was found in di/tri‐aromatic isoxazoline regioisomers prepared from acridin‐4‐yl dipolarophiles and stable benzonitrile oxides (BNO). Three alkenes, (acridin‐4‐yl)‐CH?CH‐R (R = COOCH₃, Ph, and CONH₂), reacted with three BNO dipoles (2,4,6‐trimethoxy, 2,4,6‐trimethyl, 2,6‐dichloro) to give pairs of target isoxazolines with acridine bound to C‐4 or C‐5 carbon of the isoxazoline (denoted as 4‐Acr or 5‐Acr). Regioselectivity was dependent on both the dipolarophile and dipole character. The ester and amide dipolarophile displayed variable regioselectivity in cycloadditions whereas the styrene one afforded prevailing 4‐Acr regioisomers. 2,4,6‐Trimethoxy‐BNO was most prone to form 5‐Acr isoxazolines while mesitonitrile oxide gave major 4‐Acr isoxazolines. Basic hydrolysis of the amide cycloadduct led to an unexpected isoxazolone product. The structure of the target compounds was studied by NMR, MS, and X‐ray crystallography. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterization and application of a new ultraviolet derivatization reagent for amino acids analysis in capillary electrophoresis

A new ultraviolet (UV) labeling reagent, p-acetamidobenzenesulfonyl fluoride (PAABS-F), was designed and synthesized to label and determine the amino acids by capillary electrophoresis (CE) with diode-array detector (DAD). PAABS-F is very stable and easy to synthesize. It reacted with primary or secondary amino acids very quickly under facile conditions to give corresponding derivatives in high yield with excellent sensitivity and stability. No by-products were observed in amino acid derivatives when stored at room temperature under natural daylight for at least 7 days. Both amino acids standard solution and real samples reacted with this new UV labeling reagent smoothly to form high UV-absorption derivatives. The labeled 20 standard amino acids were efficiently separated by CE and the mass detection limits (S/N = 3) were ranged from 59.3 fmol for l-tryptophan to 1.70 pmol for l-histidine.     

Preparation of Polyester Polyol from Epoxidized Palm Olein

In this work, polyester polyols with high weight average molecular weight (M_w) (M_w?10000–15000) were prepared from epoxidized palm olein (EPO_o) and a series of dicarboxylic acids (C₆–C₁₂) at elevated temperature under non‐catalyzed condition. The optimal reaction conditions were determined as 180°C for 4 h. Longer carbon chain length of dicarboxylic acids was more reactive when reacted with EPO_o. The physical appearance of the product was observed as liquid at room temperature. This palm oil‐based polyester polyol is proposed as starting material for flexible polyurethane. For reaction monitoring purposes, FTIR was used while ¹H NMR analysis was carried out to characterize the important functional groups of the products. The effects of reaction time and temperature on the M_w of the reaction mixture were also studied by GPC.     

Ring functionalization of cyclosiloxanes using electrochemically generated diorganyl silanones

Cathodic reduction of oxygen in the presence of dichloro- or dialkoxydiorganylsilanes R¹R²SiX₂ (X = Cl,OAlk) provides highly reactive intermediates, supposedly diorganyl silanones R¹R²Si=O, which readily react with cyclicpermethylsiloxanes (hexamethylcyclotrisiloxane D₃ and octamethylcyclotetrasiloxane D₄) to form ring-extended products bearing an additional R¹R²SiO fragment. In this way, various groups can beincorporated into the siloxanes framework: Ph, vinyl (Vi), Alk, OAlk, H and substituted alkyls. The process is more selective at low temperature (T ?–10°C) and when using dialkoxysilanes as starting compounds. The electrochemical activation of dichloro- and dialkoxysilanes for the reaction with siloxanes provides an alternative way to prepare functional cyclosiloxanes.     

Introducing difluoromethylene sulfonamide group via nucleophilic addition of difluoromethylene anion with aromatic aldehydes

A new fluorine-containing synthon, R¹COCF₂SO₂R² (2, R¹, R²=morpholino, piperidino, etc.), was developed for the introduction of difluoromethylene sulfonamide or difluoromethylene group. Under different conditions, 2 reacted readily with aromatic aldehydes to give the corresponding difluoromethylene-containing alcohols or diols in moderate to good yields in the presence of potassium tert-butoxide. Difluoromethylene sulfonamide group was introduced into organic compounds directly for the first time by this method.     

Simple Approach to the Highly Stereoselective Synthesis of trans-1,2-Cyclopropane Derivatives

In the presence of KF·2H2O, furoylmethyltriphenylarsonium bromide （1a） or thienoylmethyltriphenylarsonium bromide （1b） reacted with 2-[（un）substituted benzylidene]malononitrile （2） in chloroform at room temperature to give trans-3,3-dicyano-1-furoyl-2-[（un）substituted phenyl]cyclopropane （3a） or trans-3,3-dicyano-1-thienoyl-2- [（un）substituted phenyl]cyclopropane （3b） respectively in good yield with high stereoselectivity. The structures of product 3 were confirmed by IR, MS, 1^H NMR, 1^H-1^H COSY and microanalysis. The relative configuration of product 3 was determined by 1^H-1^H NOESY technique. The mechanism for the formation of product 3 was also proposed.     

Convenient high yield and stereoselective synthesis of O-glycopeptides using N-α-Fmoc-Tyr/Ser[β-d-Glc(OAc)4]OPfp generated in solution

Fmoc-AA-OPfp (AA=Tyr or Ser) (1 equiv) was reacted with β-d-Glc(OAc)₅ (6 equiv) in the presence of BF₃.Et₂O (6 equiv) in CH₂Cl₂ at room temperature for 2 h, and the glycosylation reaction mixture was used directly to couple to the amino group of the peptide resin without isolation and purification of the Fmoc-AA[β-d-Glc(OAc)₄]-OPfp. Moreover, the -OAc protecting groups of glucose was removed just prior to releasing the peptide from the resin using 6 mM NaOMe in 85% DMF-MeOH. The crude product obtained by TFA cleavage contained >90% of the target O-glycopeptide, and the 500 MHz ¹H NMR analysis revealed that the glycosylation reaction was nearly stereoselective (>97% β-anomer). This method is rapid and stereoselective, and can now be exploited for the routine synthesis of O-glycopeptides.     

Kristallstrukturbestimmung von N-Trimethylsily-N′-methylimidazoliumbromid

Crystal Structure Determination of N-Trimethylsilyl-N′-Methylimidazolium Bromide The reaction of Trimethylbromosilane and N-Methylimidazole (NMI) led to a 1:1 compound stable at room temperature. The reaction was carried out at room temperature and colorless single crystals were obtained by sublimation. The addition compound crystallizes in the orthorhombic space group Pbnb (No. 56) with lattice constants a = 1218.3(2)pm, b = 1333.6(1)pm, c = 1360.2(2)pm, Z = 8, D_calc = 1.414 g/cm³. For 1506 independent reflections, measured at 21°C the structure could be refined to R = 0.067 and R_w = 0.062.     

Highly diastereoselective aminoalkylation of naphthols with chiral amines mediated by lithium perchlorate solution in diethyl ether

One-pot, three-component, Mannich reaction of naphthols with in situ prepared imines in 5 M ethereal lithium perchlorate at room temperature affords the corresponding aminoalkylated products in high yields with high diastereoselectivities. The process is exemplified by the reaction of 2-naphthol with (R)-1-phenylethylamine and an aromatic aldehyde in concentrated ethereal lithium perchlorate solution, which affords a highly diastereoselective access to the requisite 2-aminoalkylated product.     

Efficient synthesis of cis-thiazolidinethiones derived from ephedrines

The reaction of chlorodeoxypseudoephedrine or chlorodeoxynorpseudoephedrine hydrochlorides with sodium dithiocarbonate in stirring ethanol at 0 °C to stereoselectively afford the corresponding cis-thiazolidinethiones in good yields (81% and 95%) is reported. The in situ formation of a cis-aziridine to explain the presence of trans-thiazolidinethione as a side product is proposed when the same reaction was carried out at room temperature. In addition, a 70:30 mixture of trans-isomers of a thiazolidinethione/isothiazolidinethione was formed when a cis-aziridine NH was reacted with carbon disulfide in refluxing ethanol. The analogous reaction with cis-aziridine N-Me stereoselectively affords the corresponding cis-thiazolidinethione. The ¹H and ¹³C NMR data of the thiazolidinethiones were assigned. cis-3,4-Dimethyl-5-phenylthiazolidine-2-thione was crystallized from ethanol and its X-ray diffraction structure was analyzed.     

Synthesis and structural characterization of a dichloro zinc complex of N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane: Application to ring opening polymerization of rac-lactide

A novel dichloro zinc complex (L¹)ZnCl₂, where L¹ is N,N′-bis-(2,6-dichloro-benzyl)-(R,R)-1,2-diaminocyclohexane, has been synthesized and characterized. The dimethyl derivatives, generated in situ from the well characterized dichloro zinc complexes (L¹)ZnCl₂ and (L²)ZnCl₂, where L² is N,N′-bis-(benzyl)-(R,R)-1,2-diaminocyclohexane, were employed as initiators for the ring opening polymerization (ROP) of rac-lactide (rac-LA). The complexes were found to be highly efficient initiators yielding the polylactide (PLA) with a narrow molecular weight distribution. The catalytic activity and heterotactic selectivity of the Zn(II) complexes were affected by the substituents on the phenyl groups of benzyl moieties in (R,R)-1,2-diaminocyclohexane. The dimethyl derivative of (L²)ZnCl₂ produced highly stereocontrolled PLA with P_r = 0.75 at −25 °C.