摘要:

Acylation of Tautomerizable C‐Amino‐Azoles with Amidine or Guanidine StructureAmino‐azoles can react with electrophiles to give different regioisomers. Stable ringacylated isomers were isolated at low temperatures and under neutral conditions. Acyl migrations are obtained at higher temperatures and under basic conditions to form the thermodynamic stable isomers.The different isomers can be characterized by mean of1H‐NMR,13C‐NMR, IR and mass spectrometry.The results obtained enable us to correct some confusions in the literature about the regioselectivity of the acylation of ami

ISSN:0941-1216    

DOI:10.1002/prac.19933350102

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe indolo‐2,3‐quinodimethane (5), generated from 2,3‐bis(bromomethyl)indole (4), was trapped with unsymmetrical carbodienophiles or N, N′‐p‐phenylenedimaleimide to furnish the 1,2,3,4‐tetrahydrocarbazoles (6–9). [4 + 2]‐Cycloaddition of5with tetracyanoethylene gave rise to the tetracyanocarbazole (10) and a subsequent product11aor11b. The Diels‐Alder reaction of5with divinyl sulfone was regiospecific within the detection limits of HPLC analysis. Similarly, the reaction of5with N, N′‐p‐phenylenedimaleimide yielded

ISSN:0941-1216    

DOI:10.1002/prac.19933350103

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Synthesis of New N, N,1,1‐Tetramethyl‐isobenzofuranaminesThe nitrophthalides3a–daimed as intermediates in the synthesis of the title compounds6a–dwere obtained via regioselective reduction of 3‐nitrophthalic anhydride1or by nitration of phthalide and 3,3‐dimethylphthalide, respectively. Reductive methylation of the nitro groups afforded the dimethylaminophthalides5a–dwhich in turn were reacted with MeMgI or in the case of5dreduced by LiAlH4leading finally to the ti

ISSN:0941-1216    

DOI:10.1002/prac.19933350104

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe regioselectivity ratio RS = normal: abnormal opening of activated 2‐methylaziridines2by nucleophiles is found to range from 0.10 to unmeasurable large (only normal opening = substitution at CH2by strongly basic carbanions). RS is assumed to result from SN2 variants differing in the degree to which bond breaking is ahead of bond making including perhaps synchronous SN2. Bond breaking will be more ahead for the N‐CMe bond. High nucleophilic power pushes bond making toward a synchronous process resulting in great RS. The decrease in RS with acyl activation relative to sulfonyl activation is in accord with a flattening of the nitrogen pyramid (planarization effect). The planarization effect is retained in acidic medium by O‐protonation: Rs 0.10–0.14 for methanolysis as compared to RS 0.43 for N‐protonated sulfonylaziridine2h. AM1 calculations support the planarization hypothesis. – No indication for SET with trityl anio

ISSN:0941-1216    

DOI:10.1002/prac.19933350105

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractRecently discovered 4‐trifluoromethyl‐1,3‐oxazin‐6‐ones react with electron‐poor dienophiles as 2‐aza‐1,3‐dienes in Diels‐Alder cycloadditions to give new 2‐trifluoromethyl pyridines (3a–d,4a–c). Regioselectivity is excellent in the case of unsymmetrical dienophiles. These new pyridines permit furth

ISSN:0941-1216    

DOI:10.1002/prac.19933350106

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Photochemistry of Aminoketones. XV. Photochemical Acyl Migration in N‐Tosyl‐β‐aminovinyl‐phenyl‐ketonesN‐Tosyl‐β‐aminovinyl‐phenyl‐ketones1a–iare prepared in good yields from β‐chlorovinyl‐ phenyl‐ketones by reaction with the sodium salts of tosyl amides in dry DMF at room temperature. In contrast to the relatively photostable N, N‐dialkyl‐β‐aminovinyl‐aryl‐ketones the electronically excited1give irreversible chemical reactions within a few minutes. Among other not identified photoproducts the α‐tosyl‐β‐aminovinyl‐phenyl‐ketones2were found. From the experimental results it is evident that the migration of the tosyl group prefers a radical‐type two step reaction thro

ISSN:0941-1216    

DOI:10.1002/prac.19933350107

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Conversion and Selectivity in Hydroformylation of Hex‐1‐en with Silica‐Gel‐, Silica‐Alumina‐Gel and Alumina‐Oxide‐ Supported Dicobalt Octacarbonyl and Cyclopentadienylcobalt DicarbonylThe catalytic influence of silica‐gel‐, silica‐alumina‐gel‐ and alumina‐oxide‐supported Co2(CO)8and CpCo(CO)2on the conversion and selectivity in hydroformylation of hex‐1‐en has been studied at 353 K under 120 bar syngas pressure in acetonitrile. The support systems were prepared by impregnation of SiO2(Grace), SiO2/4% Al2O3(Kali Chemie), SiO2/11% Al2O3(Kali Chemie) and Al2O3(Kali Chemie) using Co2(CO)8and CpCo(CO)2solutions in pentane, dichlormethane and 2‐chlorpropane.The results are discussed with regard to some measured relevant support characteristics. The turn over numbers especially those of silica‐gel‐ and silica‐alumina‐gel supported Co2(CO)8and CpCo(CO)2show positive effects in relation to a heterogeneo

ISSN:0941-1216    

DOI:10.1002/prac.19933350108

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Preparation of Organic Dications by Protonation of Iminium‐Salts. – NMR‐Spectroscopic Evaluation of the Topomerisation Barriers in the Bis(dimethylamino)‐dimethylammonio‐carbeniumion1,3‐Bis(dimethylamino)‐2‐aza‐2‐propenylium‐chloride (4a) is protonated by inorganic acids as HCl, HBr, HI, H2SO4, HBF4and HClO4to give the corresponding 1,3‐bis(dimethylamino)‐2‐azapropan‐1,3‐diylium‐salts (7a–f) which are isolated and characterized by elemental analysis and their1H‐NMR‐spectra.N, N, N′, N′, N″, N″‐Hexamethylguanidinium‐chloride (5a) can be protonated only by super acid systems e.g. HFSO3/SbF5. The dication thus formed presents3topomerisation barriers. Two of them are explained as restricted rotations, whereas the

ISSN:0941-1216    

DOI:10.1002/prac.19933350109

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Metalorganic Synthesis of Modified Polycarbosilanes. I. Benzylidene Bridged PolycarbosilanesBy single step reaction of the monomeric silanes diphenyl‐, phenylmethyl, dimethyl‐, methyl‐vinyl‐ and methyldichlorosilanes with α,α‐dibromotoluene as carbosilane bridge builder and magnesium as reducing agent a series of modified linear polycarbosilanes was prepared. This new synthetic route – a simple variation of the Grignard method – allowed the synthesis of the oligomeric products in large amounts. In addition, the sensitive functional groups SiH and SiCH  CH2were completely preserved during the course of the reaction, in contrast to the direct synthesis with sodium as reductive agent.The structures of the viscous polycarbosilanes were characterized by a highly rate of alternating Si‐C‐systems.The modified polycarbosilanes were analysed and investigated by IR‐,1H‐,13C‐ and29Si‐NMR‐spectroscopy. The weight and number averages Mwand Mn, which were determined by gel‐permeation chromatography, clearly reflected the oligom

ISSN:0941-1216    

DOI:10.1002/prac.19933350110

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe reaction of nitrosubstituted aryl fluorides1with cyclic β‐diketones2proceeds at 20–80°C in the presence of bases, such as KOH, KF or NaOEt, leading to the aryl ethers3a–m. Depending on the base the reaction of dimedone2aor 1,3‐cyclohexanedione2bwith 2,4‐dinitrofluorobenzene1aor 4‐fluoro‐3‐nitrobenzonitrile1bfurnishes C‐ and/or O‐arylated products. Upon heating of3g,eand3mat 40–100°C in DMF/K2CO3, the C‐arylated ketones4a–care formed in good yields. Starting from3awe obtained the chromenedio

ISSN:0941-1216    

DOI:10.1002/prac.19933350111

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY