摘要:

AbstractReductive amination, amide formation using BOP [(1H‐1,2,3‐benzotriazol‐1‐yloxy)tris(dimethylamino)‐phosphonium hexafluorophosphate] and esterificationviaDCC (dicyclohexylcarbodiimide) were the key synthetic steps to generate an advanced intermediate in the preparation of a didemnin B analog based on a sugar scaffolding (2). This analog should provide insight into the bioactive conformation of d

ISSN:0009-4536    

DOI:10.1002/jccs.200100001

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe 1,2‐H shift reactions of simple carbenes (CH2Y‐C‐X) have been studied using density functional theory (DFT). The influence of the substituent X and Y groups on the activation energy (Ea) of 1,2‐H shifts were examined. The ‘by stander’ Y substituents lower Eain the order of Me, F>Cl, Br>H. Our analysis shows that the X effect is more significant than the by stander Y effect. X substitutions increase Eaof carbenes in the order of F>Cl>Br>Me>H. The influence of X on Eais governed by the singlet‐triplet energy separation (ΔES‐T) of the carbene, i.e., Eaof a carbene is larger as its ΔES‐Tin creases due to an X substitution. The X effect was also found to be related to the magnitude of the exothermicity: Ea of reaction is smaller when the reaction is more exothermic. Origin of the Y effect is attributed to the inter play between two factors: ‘lateness’ of transition state on the potential energy surface, and the exothe

ISSN:0009-4536    

DOI:10.1002/jccs.200100002

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractDiamino‐carbene ligand transfer between various metalions is studied, particularly with Pd (II) to Rh(I), Rh(I) to Au(I). Reactions of various carbene complexes with AgPF6result in the cleavage of the M=C bond to give the protonated carbene species, imidazolidin‐2‐ylidinium salt, indicating the presence of free carbene ligand in the reaction medium. When the carbene transfer process was carried out in tetrahydrofuran, the polymerization of tetrahydrofuran occ

ISSN:0009-4536    

DOI:10.1002/jccs.200100003

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractMacrocyclic polyethers, e.g., crown ethers and cryptands, were prepared and employed as phase transfer catalysts for free radical polymerization of acrolein, a vinyl monomer, with persulfates (S2O82–) as initiators. The catalytic abilities of various macrocyclic polyethers as catalysts for the free radical polymerization of acrolein were found to be in the order: benzo‐15‐crown‐5>dibenzo‐18‐crown‐6>12‐crown‐4>15‐crown‐5>18‐crown‐6>cryptand‐22 with sodium persulfate (Na2S2O8) as initiator. Sodium persulfate proved to be a better initiator than ammonium persulfate or potassium persulfate with benzo‐15‐crown‐5 as a catalyst. Effects of solvents and temperature on the catalytic polymerization were also investigated. The polymerization rates in various solvents were in the order: dioxane>benzene>acetonitrile>acetone>dichloromethane>hexane>water. Comparison between bulk polymerization and solution polymerization was also made. Higher polymerization rate was observed at higher temperature. The molecular weights of polyacrolein and the conversion of monomer in reaction period were determined with gel permeation chromatography and ultra‐violet spectrophotometry, respectively. Concentration effects of crown ether and initiator w

ISSN:0009-4536    

DOI:10.1002/jccs.200100004

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe electrochemical character of polyaniline/thiokol rubber (PANI/TR) composite film on a Pt electrode was investigated in a cysteine sulphuric acid solution by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The significant change of the peak current and peak potential in the cyclic voltammograms was observed. The irreversible peaks of cyclic voltammetry for cysteine/cystine redox couple at a platinum electrode have turned into one pair of nearly reversible peaks at the above electrode; the reversibility of the redox couple has been greatly improved. We found that thiokol rubber could improve the electrocatalysis of the PANI film to the electrochemical reaction with S‐S bonds, as well as the adhesion of the PANI film to the Pt substrate. Several effective factors, such as the concentration of thiokol rubber in the nonaqueous electrodeposition solution, different potential scan rate, immersing time of the film electrode in the studied electrolyte were all taken into accoun

ISSN:0009-4536    

DOI:10.1002/jccs.200100005

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractA new reagent system using rhodamine‐B dye for the determination of selenium is described. The method is based on the reaction of selenium with acidified potassium iodide to liberate iodine. The liberated iodine bleaches the pink colour rhodamine‐B, which is measured at 555 nm. Beer's law is obeyed over the concentration range of 1–10 μg of selenium final solution volume of 25 mL (0.04–0.4 ppm) and the apparent molar absorptivity and Sandell's sensitivity was found to be 1.96× 105l mol−1cm−1and 0.0004 μg cm−2, respectively. The method is simple, sensitive, and selective and is satisfactorily applied to micro‐level determination of selenium in various environmental an

ISSN:0009-4536    

DOI:10.1002/jccs.200100006

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThis paper describes the synthesis of some pyrimido[2,1‐b]benzothiazol‐8‐yl sulphones (7, 9, 11, 13, 14, 16) starting from bis[2‐aminobenzothiazol‐6‐yl)sulphone 1. Reaction of 1 with acetic anhydride and/or benzoyl chloride gave substituted amino derivatives2a,b, whereas its reaction with phenacyl bromide and/orp‐chlorophenacyl bromide gave imidazo benzothiazol‐7

ISSN:0009-4536    

DOI:10.1002/jccs.200100007

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe synthesis of α‐pyrazolylglycine derivatives(7a‐d) with different substituents, starting from glycine have been pre pared. The spectroscopy of intermediate compounds and the final amino acids have been discu

ISSN:0009-4536    

DOI:10.1002/jccs.200100008

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractThe recently described pressure reaction in the presence of trithylamine with subsequent thermal (200°C) cyclization provided 13N‐pyridylcantharidinimides4a‐4mfrom aminopyridines and cantharidin in yields of 15–83%. 2‐Amino‐3,5‐dichloropyridine faile

ISSN:0009-4536    

DOI:10.1002/jccs.200100009

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY

摘要:

AbstractSeveralC‐butenyl linked disaccharides were pre pared in high yields by olefin cross‐metathe

ISSN:0009-4536    

DOI:10.1002/jccs.200100010

出版商:WILEY‐VCH Verlag    

年代:2001

数据来源: WILEY