摘要:

AbstractSultones are readily prepared by intramolecular Diels–Alder reaction of vinylsulfonates in an often highly stereoselective fashion. Various methods for the synthetic elaboration of these heterocycles have been developed and applied to the total synthesis of biologically active natural product

ISSN:0941-1216    

DOI:10.1002/prac.19983400102

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

ISSN:0941-1216    

DOI:10.1002/prac.19983400103

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractStarting from 3‐acylaminobenzo[b]furan‐2(3H)‐ones (2) 3‐arylthio substituted derivatives (3) were preparedvianovelN‐acylimines (5). Compounds of type3and5were found to show visible chemiluminescence upon base‐induced oxidation in the presence of an oxygen source. A mechanistic interpretation for this chemiluminescence reaction

ISSN:0941-1216    

DOI:10.1002/prac.19983400104

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractReductive cyclization of the 1‐hydroxy‐3‐(3‐oxoalkyl)‐9,10‐anthraquinones2, 9and10yields the angularly condensed cyclopenta[a]anthraquinones3, 21and22aunder neutral conditions (DMF/Na2S2O4). By contrast, the linear cyclopenta[b]anthraquinone23is isolated from10applying the usual alkaline Marschalk conditions (aqueous methanol, NaOH, Na2S2O4). The linearly condensed 5,12‐naphthacenequinones24–28of different degree of saturation are obtained in good combined yield from the corresponding 1‐hydroxy‐3‐(4‐oxoalkyl)‐9,10‐anthraquinones19and20under the condition

ISSN:0941-1216    

DOI:10.1002/prac.19983400105

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractA series of 2‐amino‐substituted 5,6‐benzo‐2H‐pyrans14, 2‐alkylidene‐5,6‐benzo‐2H‐pyrans15, and their dimers17are obtained, depending on the condition used, by the reaction of 2‐hydroxy‐benzaldehydes1with enamines9derived of (cyclo)aliphatic ketones. Compounds14, 15, and17can be transformed into 2‐alkyl‐benzopyrylium salts16or 2‐[1‐(2‐hydroxyphenyl)‐alken‐2‐yl]‐benzopyrylium salts23by treatment with mineral acids. With aromatic aldehydes or the Vilsmeier reagent the compounds14, 15, or17are transformed into deeply colored 2‐(aryl‐alkenyl)‐benzopyrylium perchlorates25or 2‐(2‐dialky

ISSN:0941-1216    

DOI:10.1002/prac.19983400106

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

Investigations on Adhesion of Pigment Printings by UV‐Laser TreatmentInvestigations on the influence of UV‐laser treatment of polyethyleneterephthalate and polyamide fibers and foils on the adhesion properties of pigment printings are presented. It could be shown that even irradiation with low energy densities and low number of pulses applied increases binder film adhesion very efficiently. Some interpretations of the laser action upon adhesion improvement related to surface modification are presen

ISSN:0941-1216    

DOI:10.1002/prac.19983400107

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

Abstract2‐Amino‐4,5‐dihydro‐3‐furancarbonitriles (1) react with a slight excess of dibenzoyldiazomethane in the presence of rhodium(II) acetate to give 1,3‐oxazin‐4‐ones (2). With three equivalents of dibenzoyldiazomethane compounds1react to afford furo[2,3‐b]pyran‐3a‐carbonitriles (3). Compound3awas also obtained by treatment of2awith two equivalents of

ISSN:0941-1216    

DOI:10.1002/prac.19983400108

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

The Decomposition of Acidic Karl Fischer Reagent in MethanolThe reaction between sulfur dioxide and iodine in methanol is started by traces of water in the solvent. Hydrogen iodide is formed and reacts with methanol to produce more water until all iodine is used up. An addition compound between iodine and hydrogen sulfite was found as an intermediate and characterized by Raman spectroscopy. Elementary sulfur is formed in a second reaction.

ISSN:0941-1216    

DOI:10.1002/prac.19983400109

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

1,3‐Dithienium and 1,3‐Dithiolenium Salts. IX. Reactions of 1,3‐Dithiane‐2‐ylium Tetrafluoroborates withC‐Nucleophiles1,3‐Dithian‐2‐ylium tetrafluoroborates (1), which can be easily obtained by variable methods, react in good to excellent yields with variable C‐nucleophiles to new geminal disubstituted 1,3‐dithianes. The latter compounds are potential precursors of interesting synthetic building blocks. Reactions are described with 2‐lithio‐1,3‐dithianes2, sodium cyanide4, sodium salts of the nitro alkanes7and CH‐acids of the type of the 1,3‐dicarbonyl compounds9. The reduction of 3‐oxo‐2‐(2‐phenyl‐1,3‐dithian‐2‐yl)‐ethoxybutanoat–following a diastereoselective pathway – leads to the Cram product11. Further presented is the crystal structure of

ISSN:0941-1216    

DOI:10.1002/prac.19983400110

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

Concerning the Products of the Reaction of Methyl Bromide and Ethyl Bromide with Potassium Hydroxide in Aqueous Methanolic Solutions and the Progress of this SN2‐ReactionInvestigations of the reaction of methyl bromide and ethyl bromide with potassium hydroxide in methanolic and aqueous methanolic solutions show that the main products of these reactions are dimethyl ether and ethylmethyl ether. The reaction rates measured in methanolic or aqueous methanolic solutions are the same whether potassium hydroxide or potassium methoxide are used. These results are caused by an equilibrium between hydroxide and methoxide ions with which we could establish the equilibrium constant near 0.6. This means that a solution of sodium hydroxidec= 0.1 moll−1in methanol contains roughly 99.8% of methoxide ions. The reaction rates in methanolic as well as in aqueous methanolic solutions are strict second order. The reaction rate measured at several temperatures permitted the calculation ofEA≠, ΔH≠, ΔS≠and ΔG≠. Furthermore the kinetic investigations show that the nucleophilicity of methoxide ions is lower compared to hydroxide ions. The calculation of the Swain–Scott‐parameternresults in a nucleophilicity scale in order to methoxide, hydroxide, ethoxide ions. The kinetic investigations of the reaction of ethyl bromide with methoxide and hydroxide ions in methanolic solutions demonstrate that at high temperatures the rate constant of methoxide ions is higher than that of hydroxide ions. The opposite case can be observed at lower temperatures. At the temperature of 20 °C the rate constants of both reactions are equal. This is to do with the isokinetic effect which one is rarely able to observe a

ISSN:0941-1216    

DOI:10.1002/prac.19983400111

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY