摘要:

AbstractA multistep procedure for the conversion of ergosterol into the tetrahydropyranyl ether of (24R)‐24,25‐dihydroxyprovitamin D3using 1,4‐dihydrophthalazine‐1,4‐dione as diene protecting agent was compared with an established route, which uses 4‐phenyl‐1,2,4‐triazoline‐3,5‐dione for the protection of the diene system. The disclosed reaction sequence allows to double the overall yield. The 1,4‐dioxo‐1,2,3,4‐tetrahydrophthalazin‐2,3‐ylene group proved to be the better diene protecting group in the ozonolytic degradation of the ergosterol side chain. Maintaining the protecting group in the next reaction steps offered further advantages by diminishing the air and light sen

ISSN:0021-8383    

DOI:10.1002/prac.19883300402

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

Free Radical Reactions of N‐Heterocyclic Compounds. VIII. ESR‐Investigations on the N,N‐Bond Cleavage Reaction of Cylic 2,2‐Diacyclhydrazinoxyls2,2‐Diacylhydrazinoxyls (2) undergo decomposisition to new nitroxides3in the presence of bis (acetylacetonato) cobalt (II), tert.‐butyl hydroperoxide and an alcohol (i.e. methanol, ethanol, i.‐propanol). These new radials3are spin trap products of nitrosoarenes, formed by a fragmentation process of 2 and of ligand radicals, generated from bis (acetylacetonato) cobalt (II) by oxidation with tert.‐butyl hydroperoxide. The e. s. r. data of the radicals2,3and of the3‐isomeric radicals

ISSN:0021-8383    

DOI:10.1002/prac.19883300403

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

Pyrazolinone Ring Closure with Alkoxy MigrationAlkyl 3‐(4‐nitro‐phenylazo)‐2‐brom‐2‐butenoates (1a,b) with morpholine undergo substitution of the bromo group and ring closure connected with a migration of the alkoxy group forming 4‐alkoxy‐3‐methyl‐4‐morpholino‐1‐(4‐nitro

ISSN:0021-8383    

DOI:10.1002/prac.19883300404

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractMonothiomalonamides (1a,b) coupled with arenediazonium salts yield the α‐arylhydrazone derivatives (2a—c), Reaction of1a,bwith α‐haloketones afforded polysubstituted thiazoles6a—c. Compounds6condensed with p‐nitrosodimethylaniline and coupled with arenediazonium salts yield the azomethine derivatives7a—dand the arylhydrazones8a—h, respectively.Compounds1a,bbehave differently towards hydrazonyl chlorides, they yielded arylazodimethylthiazoles13a—cand thiazolylacetanilides

ISSN:0021-8383    

DOI:10.1002/prac.19883300405

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractThe reaction of phenyl isocyanate with n‐butanol in the presence of tertiary amines has been kinetically studied as a model process for the polyurethane formation under conditions similar to those of industrial scale production. The rate‐determining step is believed to be the nucleophilic attack of tertiary amine on an associate of isocyanate with alcohol which is then converted into a very reactive uronium salt. This salt reacts fast with alcohol giving the final product, the ureth

ISSN:0021-8383    

DOI:10.1002/prac.19883300406

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractA comparative kinetic study for the reaction of aryl isocyanates with alcohols in the presence of organotin compounds has been performed. It has been found that the transfer of an alkoxide ion from tin to isocyanate is the rate‐determining step. This transfer occurs within a complex formed in two rapid preequilibrium processes between either tin compounds and alcohol or isocyanate, respectivel

ISSN:0021-8383    

DOI:10.1002/prac.19883300407

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractA series of 5‐substituted aryloxymethyl‐1,3,4‐oxadiazole‐2‐thione (3a–e) and their Mannich bases4–8are synthesized and subjected to fungitoxic screening. The structures of these compounds are established on the basis of elemental analysis1H‐n.m.r. and mass spectral data. The mass spectral fragmentation pathways of these compound

ISSN:0021-8383    

DOI:10.1002/prac.19883300408

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractReaction of C‐ethoxycarbonyl‐N‐arylnitrilimines (2a–d) with α, β‐disubstituted acrylonitriles (3a–f) in refluxing benzene affords the corresponding substituted pyrazoles5a–fand6a–crespectively in good yield. However, reaction of2a–ewith3ggives the 2‐pyrazoline derivatives7a–d. The assigned structures for the products5–7were confirmed by their spectra (i.r.,1H‐n.m.r.) and elemental analyses. Also the structures of the pyrazoles5were substantiated by compariso

ISSN:0021-8383    

DOI:10.1002/prac.19883300409

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

AbstractSolvatochromic and halochromic behaviour in the u.v.‐vis absorption spectra of some substituted 4‐arylidene‐2‐aryloxazol‐5‐ones (1–5) are studied. Positive and negative solvatochromism, depending on the substituent present, are observed in different hydrogen bonding donoracceptor (HBD‐A) and hydrogen bonding acceptor (HBA) solvents. However, in non hydrogen bonding (NHB) solvents all compounds show a positive solvatochromism. A considerable intramolecular charge transfer interaction, between the donor and acceptor parts in the oxazolones studied, is observed. Small fluorescence quantum yields are observed for the oxazolones. In triethanolamine‐acetone mixtures, the visible absorption spectra of the hydroxy substituted oxazolone shows an additional long‐wavelength band suggesting the existance of prototropic equilibria. The prototropic equilibrium constants at different temperat

ISSN:0021-8383    

DOI:10.1002/prac.19883300410

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY

摘要:

Water Soluble Disulphonated Aromatic Ketones — Photophysical and Photochemical PropertiesBy the sulphonation of benzophenone, xanthone, thioxanthone, acridone, and methylacridone the disulphonated derivatives BPS, XS, TXS, AcS and MAcS are produced. Their disodium salts are well soluble in water. The absorption and the emission spectral data of these ketones are similar to those of the respective parent compounds. The S1state of BPS alone is of n — π* type, in all the other cases it possesses mainly π — π* character. The S1states can serve as donors in electron transfer reactions with iodonium salts. The kinetic curves of flash photolysis of these ketones in water show two decay processes, which are attributed to the triplet state and the long living ketyl radical. The triplet absorption spectra of the disulphonated ketones are very close to those of the unsubstituted ketones, but the life times of the former are much higher. The T1are quenched through onium salts by electron transfer reactions. Acryl amide, too, acts as a quencher for the

ISSN:0021-8383    

DOI:10.1002/prac.19883300411

出版商:WILEY‐VCH Verlag GmbH    

年代:1988

数据来源: WILEY