摘要:

AbstractTo illustrate the flexibility of modern asymmetric synthesis six alternative routes are presented for the preparation of the novel antidepressant Rolipram®. The routes are based on optical resolution, on the concept of “ex‐chiral pool synthesis” with lactic or tartaric acid as the starting materials, and on the application of chiral auxiliaries. The relative efficiency of the routes is dis

ISSN:0941-1216    

DOI:10.1002/prac.19943360402

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Investigations on the Conformational Variety of Mono‐ and 2,5‐Dialkoxy Substituted Poly(1,4‐phenyleneethenylene)sThe alkoxy substituted poly(1,4‐phenyleneethenylene)s1and2can principally exist in an enormous variety of conformers (table 1). However, force field calculations (MMX) reveal a far‐reaching restriction to a relatively small number of non planar conformers with minimized steric energy. The decisive criterion is due to the interaction between the oxygen atoms and the olefinic hydrogens. An increasing steric hindrance should lead to higher twist angles θ in the main chain and hence to a shorter effective conjugation length. Such an effect could play a minor role between the unsubstituted parent compound and1/2, but UV/Vis‐ and fluorescence spectra don't give any hints for a change of the effective conjugation length n ≈

ISSN:0941-1216    

DOI:10.1002/prac.19943360403

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Investigations on the Photoconductivity of Alkoxy Substituted Oligo‐ and Poly(1,4‐phenyleneethenylene)sThe photoreactivity and the photoconductivity of the mono‐ and dialkoxy substituted oligo‐ and poly(1,4‐phenyleneethenylene)s1/1′a‐nwere investigated in order to optimize the photoconducting properties of these materials. Increasing the length of the side chains enhances the average length of the main chain during the polycondensation and decreases the band gap till the limit of convergence is reached. The highest photoconductivity was observed for the 2,5‐dipropyloxy system1/1′j. Longer side chains render the charge transfer from chain to chain more difficult. The measurements were performed in dispersion layers and related to the industrial standard3. Compound1mwas also measured in a pure state as transparent film and compared to a poly(N‐vinylcarbazole) film which shows a dye‐sensitized photoconductivity. In both cases the optimized systems1/1′ were markedly superior to the standards. The highest sensitivity could be observed for wavelengths λ lying close to the absorption maxima λmax. The compounds1/1′ have a high photostability on irradiation with visible light; however, they are rapidly des

ISSN:0941-1216    

DOI:10.1002/prac.19943360404

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Ring Transformations of Heterocyclic Compounds. VII. 2,4,5‐Triarylbenzophenones from 2,4,6‐Triarylpyrylium Salts and Arylacetaldehydes: First Pyrylium Ring Transformations with Aldehydes as Carbon Nucleophiles2,4,6‐Triarylpyrylium salts1react with arylacetaldehydes2in the presence of sodium acetate in ethanol by a 2,5‐[C4+C2] ring transformation to give 2,4,5‐triarylbenzophenones3in high yield. Besides the sodium acetate, sodium methanolate, triethylamine, triethylamine/acetic acid or piperidine acetate can be applied as condensing agent. The reaction represents the first pyrylium ring transformation initiated by

ISSN:0941-1216    

DOI:10.1002/prac.19943360405

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Liquid‐phase Oxidation of 1,2‐Ethane DiolThe oxidation rate and the kind of oxidation products in the reaction of 1,2‐ethane diol (1) with molecular oxygen in liquid phase at 150°C were investigated.1has a very low oxidation rate. Cu‐, Zn‐, Fe‐, Co‐ and Al‐acetylacetonates as catalysts increase the reaction rate. The main‐products of the investigated reaction are the 1,3‐dioxolan (2), the 2‐methyl‐1,3‐dioxolan (3) and the 2‐methylol‐1,3‐dioxolan (4). The formation of formic and acetic acids and of the 1,3‐dioxo

ISSN:0941-1216    

DOI:10.1002/prac.19943360406

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractReactions of 2,4‐dichloroquinolines (2a–f) with sodium azide in DMF lead either regioselectively to 4‐azido‐2‐chloroquinolines (3a–f) or with excess of sodium azide and catalysts to 5‐azido‐tetrazolo[1,5‐a]quinolines (4a–f). 2,4‐Dichloroquinolines (2g–i) having electron donating substituents in 3‐position react with sodium azide in DMF to a mixture of 4‐azido‐2‐chloroquinolines (3g–i) and 5‐chlorotetrazolo[1,5‐a]quinolines (5g–i). When the reaction of the 2,4‐dichloroquinolines (2a–i) with sodium azide is carried out in ethanol with addition of methanesulfonic acid, regioselectively 5‐chloro‐tetrazolo[1,5‐a]quinolines (5a–i) are obtained. Structural assignments of3and5have been carried out by13C‐NMR spectra, IR spectra and degradation reactions of the azido‐ and tetrazolo group to aminoquinolines (7and10) via iminophosphoranes (8and9). It could be shown that in 2‐azido/tetrazolo‐quinolines (

ISSN:0941-1216    

DOI:10.1002/prac.19943360407

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Robustness and Susceptibility as Descriptors for the Validation of Analytical SystemsThe use and meaning of robustness and similar terms well known but not defined in quality control and validation are discussed. Susceptibility is recommended as a numerical descriptor. Since limited errors of analytical signals can be tolerated and small deviations of method variables cannot be avoided susceptibility is defined as Ai,j=ΔSi,max/ΔVj, the maximum variation Δ of the analytical signal Sicaused by a variation Δ of the system variable j on its level Vj. The need of rational discussion of and consensus on tolerable variations Δ is stre

ISSN:0941-1216    

DOI:10.1002/prac.19943360408

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractAn improved synthetic access for the construction of 4,6,7‐trimethylbenzofurans (B1–B8) through the one‐electron oxidation of mesityl‐substituted enols (E1–E8) is presented. The transformation can be accomplished in good to excellent yields by using various oxidants; i.e. tris(1,10‐phenanthroline)iron(III) hexafluorophosphate, FeCl3, Ce(NH4)2(NO3)6, Cu(OTf)2/Cu2O or anodi

ISSN:0941-1216    

DOI:10.1002/prac.19943360409

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

Abstractα‐Amidoalkylation of allyltrimethylsilane with (−)‐ and (+)‐menthyl‐2‐(o–Chlorobenzoylamino)‐2‐halogenoethanoate (2, 4aand4b) gave in the presence of zinc chloride, separable mixtures of the diastereomers (−)‐ and (+)‐menthyl‐2‐(o–Chlorobenzoylamino)‐4‐pentenoate (5a, 5band6a, 6b). The absolute configurations of5a, 5band6a, 6bwere determined through conversion of5a

ISSN:0941-1216    

DOI:10.1002/prac.19943360410

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY

摘要:

AbstractThe target compounds21–27were synthesizedviabromination of the N,N,1,1‐tetramethylisobenzofuranamines13, 15and16, subsequent bromine‐lithium exchange and reaction with propanal or propanoyl chloride, respectively. In the course of some model reactions undertaken to test a synthetic strategy based on directedortho‐lithiation governed by the dimethylamino‐group a useful synthesis of the ketone3was

ISSN:0941-1216    

DOI:10.1002/prac.19943360411

出版商:WILEY‐VCH Verlag GmbH    

年代:1994

数据来源: WILEY