摘要:

AbstractThe aldol addition is the classical method for the construction of carbon chains with oxygen functionality in 1,3‐distance. Depending on whether an α‐substituted or an α‐unsubstituted enolate is allowed to react with an aldehyde, two or one stereogenic centers are created. A large number of stereoselective variants developed in recent years enable to obtain nonracemic β‐hydroxy‐carbonyl compounds. This article reports on aldol additions of carboxylic esters and thioesters which deliver nonracemic β‐hydroxycarboxylic acids in a stereoselective manner. In this context, the report emphasizes on aldol additions with triphenylglycol derived acetates

ISSN:0941-1216    

DOI:10.1002/prac.19933350802

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Synthesis of Bis(1‐phenoxy‐propen‐2‐yl)‐sulfanes derived from Bis(1‐chloro‐3‐phenoxy‐prop‐2‐yl)‐sulfanes with Potassium‐tert.‐butoxid – Determination of the E,E‐ConfigurationBis(1‐chloro‐3‐phenoxy‐prop‐2‐yl)‐sulfanes (1), anti‐MARKOVNIKOV 2:1‐adducts of allylphenyl ethers with sulfur dichloride at low temperature are transformed in the presence of potassium‐tert.‐butoxid by dehydrohalogenation / prototropic rearrangement to phenoxyvinyl sulfanes, the E,E‐bis(1‐phenoxy‐propen‐2‐yl)‐sulfanes3. Sulfanes3are of special interest as a model for unsaturated macrocyclesBderivated from dithiacrown ethersA. The configuration was assigned using1H‐n.m.r.‐ and13C‐n.m.r.‐spectroscopy. The molecular structure was determinded by X‐ray diffraction techniques. Rearrangement of sulfur‐substituted allyl ethers2to the propenyl isomers3aproceeds in a

ISSN:0941-1216    

DOI:10.1002/prac.19933350803

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

On the Structural Analytical Application of „Anomalous”︁ Multiplets in Off‐resonance Decoupled13C NMR Spectra of CH  CHFragmentsThe theoretical background of “anomalous” splitting of signals of molcular fragments CHCH in off‐resonance decoupled13C NMR spectra is described. The use of these splitting phenomena on the determination of vicinal H,H and geminal C,H coupling constants is demonstrated using simple examples. The possibilities to determine the configuration of double bonds are shown by other examples from the field of natur

ISSN:0941-1216    

DOI:10.1002/prac.19933350804

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

AbstractThe chosen silane coupling agents consist of a polybutadiene skeleton with Si(CH3)2OCH3or Si(OCH3)3pendent groups hydrolyzable on the glass surface. Their number, and therefore the amount of potential bonds, can be varied. These modified polybutadiene polymers act as primer compatible with the polybutadiene coating to be deposited.The subsequent cross‐linking of the double bonds of the silane primed surface with polybutadiene is initiated by benzoyl peroxide, creating chemical bonds between the solid support and its coating.The strength of the adhesion of polybutadiene to glass is measured by the 180° peel test and the values are compared with a non‐modified glass

ISSN:0941-1216    

DOI:10.1002/prac.19933350805

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Organic Syntheses Based on 2‐Oxoglutaric Acid. III. Synthesis and Reactions of Dimethyl (E)‐2‐oxoglutaconateDimethyl (E)‐2‐oxoglutaconate1obtained by dehydrobromination of dimethyl 3‐bromo‐2‐oxoglutarate reacts with o‐phenylendiamine to form the quinoxalin‐2(1H)‐one2, and with phenylhydrazine to yield the 4,5‐dihydropyrazole3. Furthermore, a Doebner‐von Miller‐type reaction affords the 8‐carboxy quinoline derivative4. Finally, addition of bromine leads diastereoselectively to the racemate of dimethyl 3S,4R‐ an

ISSN:0941-1216    

DOI:10.1002/prac.19933350806

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

α‐Methylated Fencholenic and α‐Campholenic Aldehyde – Synthesis and ReactionsThe syntheses of α‐methylated fencholenic (6a) and α‐campholenic aldehyde (6b) via the corresponding azomethines (5) are reported. Aldol condensations of6a, bwith following reductions give the allylic alcohols (12–16) and hydrogenation the saturated alcohols (17–21) with strong woody odors, some of the allylic alcohols resembling that of sandal wood. Simple reduction or oxidation of6a, bgive the alcohols (24, 27), ethers (26), esters (23, 25, 28) and ketones (29) which have interesting woody odors with spicy, earthy and

ISSN:0941-1216    

DOI:10.1002/prac.19933350807

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

Acyclic Stereochemical Analysis. III. Estimation of the Preferred Conformers of Substituted γ‐Chloropropyl‐methyl Ethers by NMR Spectroscopy and Molecular ModellingThe conformers of the various stereoisomers of a series of γ‐chloropropyl methyl ethers1–4with 1, 2 and 3 chiral centres have been estimated byMolecular Modelling (MOBY)and the results compared with the data of previous1H and13C NMR studies. The calculations corroborate former NMR results and the remarkable potential of both NMR spectroscopy and Molecular Modelling to assign even four diastereomers of acyclic molecules with three chira

ISSN:0941-1216    

DOI:10.1002/prac.19933350808

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

摘要:

The Mutual Promotion Effect of Molybdates in Multicomponent Molybdate CatalystsMulticomponent molybdate catalysts (e.g. of the composition Bi2Fe1,5Co7Cr10Mo19Oy) are produced by coprecipitation, drying and calcination. These catalysts exhibit high activity and selectivity in the ammoxidation of propene to acrylonitrile. The individual molybdates (Co‐, Fe‐ and Cr‐molybdate) exhibit no selectivity in the ammoxidation of propene. Therefore a mutual promotion effect of these molybdates exists. The cause of the promotion effect is the formation of the active and selective phase from the β‐phase of Co‐molybdate by exchange of protons with ions of Fe3+and Cr3+from the molybdates of Fe and Cr. The structure of this catalytic active and selective phase is similar to the structure of the β‐phase of

ISSN:0941-1216    

DOI:10.1002/prac.19933350809

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

ISSN:0941-1216    

DOI:10.1002/prac.19933350810

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY

ISSN:0941-1216    

DOI:10.1002/prac.19933350811

出版商:WILEY‐VCH Verlag GmbH    

年代:1993

数据来源: WILEY