摘要:

AbstractAn account of the most commonly used reagents for the introduction of the benzeneselenyl (phenyl seleno) group is given. The review focuses on the various methods of its introduction as auxiliary, modifying or protective entity, and its subsequent removal, thereby often promoting other reactions as cyclizations or double bond formation. Less emphasis is laid on reactions of the phenylselenenylated intermediates with the PhSe‐group left intact utilizing its stabilizing properties on charged intermediates, on reagents with a modified phenyl group,e.g.chiral derivatives, or on reactions not involving intermediate CSe‐bond form

ISSN:0941-1216    

DOI:10.1002/prac.19983400302

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractReactions of 1‐O‐trimethylsilyl‐glycoses, 1‐O‐acylglycoses and glycosyl fluorides, respectively, with silylated alcohols (glycodesilylations) are summarized. Synthetic strategies toward oligosaccharides using glycodesilylations are discussed as well and some typical experimental procedures

ISSN:0941-1216    

DOI:10.1002/prac.19983400303

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractA series of new 3,1′‐bridged 2‐[2′‐(4″‐dialkylaminophenyl)ethenyl]‐4,6‐diarylpyrylium perchlorates (3), 2‐[2′‐(4″‐dialkylaminophenyl)ethenyl]‐7‐diethylamino‐1‐benzopyrylium perchlorates5–8, 2‐[4′‐(4″‐dialkylaminophenyl)butadien‐1′,3″‐yl]‐, and 2‐[2′‐(7″‐diethylaminocoumar‐3″‐yl)ethenyl]‐7‐diethylamino‐1‐benzopyrylium perchlorates10–12were synthesized and characterized by means of elemental analysis,m.p., Vis/NIR, and1H NMR spectra. Semiempirical MO calculations were performed to elucidate the essential features of the chromophores. The size of the bridging ring strongly affects the geometry of the chromophores which, in turn, determines the extent of charge transfer of the longest wavelength electronic transition. Increasing deviation

ISSN:0941-1216    

DOI:10.1002/prac.19983400304

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractSeveral 4‐ protected D‐glucopyranosides were synthesized and cleaved by sodium metaperiodate. Depending on the protection pattern the resulting dialdehydes showed different types of structures. Predominantly dioxane structures of the hemiacetal or hemialdal type were obtained with preferredtransorientation of theexooxygen groups at C‐1 and C‐2. The dialdehyde derived from methyl 4‐O‐methyl‐α‐D‐glucopyranoside was treated with various C‐nucleophiles. A higher reactivity of the aldehyde function at the former C‐3 in comparison to C‐2 and a special stability of dioxane type structures for glycol cleavage dialdehy

ISSN:0941-1216    

DOI:10.1002/prac.19983400305

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractPentafluorophenyluronium salts and related coupling reagents for the solid‐phase synthesis of peptides and glycopeptides have been developed and employed in the synthesis of a glycopeptide sequence from the cell adhesion molecule E‐CA

ISSN:0941-1216    

DOI:10.1002/prac.19983400306

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe bis(acetone) complex of tetramethylrac‐3,3,7,7‐tetramethyl‐trans‐5‐palladatricyclo[4.1.0.02,4]heptane‐1,2,4,6‐tetracarboxylaterac‐1awas crystallized and investigated by X‐ray structure analysis. Unlike in complexes with bidendate ligands inrac‐1a· 2(acetone), only a small deviation from the square planar coordination of palladium was observed. Efforts to crystallize the analogous pyridine, acetonitrile and benzonitrile complexes failed; but the labile complexesrac‐1a· 2([D5]pyridine) andrac‐1a· 2([D3] acetonitrile) as well asrac‐1a· 2([D6]acetone) could be characterized by1H and13C NMR spectra and a fast ligand exchange was proven by nmr. Then the ability of different 1,2‐disubstituted cyclopropenes to formtrans‐5‐pallada‐tricyclo[4.1.0.02,4] heptanes1was investigated. Only the diesters5c–elead to PTHs, with a diester possessing sterically demanding substituents in 3‐position of the cyclopropene and with other substituents in 1‐ respectively 2‐position of the cyclopropene either the cyclo

ISSN:0941-1216    

DOI:10.1002/prac.19983400307

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

Reactivity and Selectivity in the Oxidation of Styrene Derivatives. IV. Studies on the Oxidation of Substituted β,β‐DimethylstyrenesThe liquid phase oxidation of substitued (p‐MeO‐,p‐Cl‐,m‐CF3‐) 2‐aryl‐3‐methyl‐but‐2‐enes, of 1,1‐diphenyl‐2‐methyl‐propene, of 1‐ethoxy‐2‐methyl‐1‐phenyl‐propene and of 9‐isopropylidene‐fluorene with pure oxygen was investigated in chlorobenzene solution and in presence of cumene and of cumene hydroperoxide in the temperature range 65‐125 °C. The product yields were determined gaschromatographically. The differences of the activation energies of epoxide formation and the parallel reactions were calculated. They amount to 19–48 kJ/mol. The epoxide selectivity increases with increasing temperature and increasing concentration of olefin. The relative chain propagation constants (kpCC) were determined by competitive oxidation with cumene. The kpCCvalues of substitued β,β‐dimethylstyrenes can be correlated b

ISSN:0941-1216    

DOI:10.1002/prac.19983400308

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractThe synthesis and stereochemical characteristics of pyrrolidino‐, isoquinolino‐ and indolo‐enaminones2–11are reported. The inhibition of cyclooxygenase was determined in a bovine thrombocyte intact cell assay and that of 5‐lipoxygenase using intact bovine polymorphonuclear leucocytes. Except compound2c′ which is a well‐balanced dual inhibitor of both enzymes, all other enaminone derivatives are weak inhibitors of both cyclooxygenase and 5‐lipoxygenase. Structure‐activity relationships of the enaminones in relation to known anti‐inflammatory

ISSN:0941-1216    

DOI:10.1002/prac.19983400309

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

Abstract2,3,4,5,6‐Penta‐O‐acetyl‐D‐galactonic acid chloride (1a) andD‐gluconic acid chloride (1b), respectively, react with alkyl acetoacetates and benzoylacetates2, respectively, to yield derivatives3of diuloses with an alkoxycarbonyl group in the branch. Decarboalkoxylation of these compounds gives 1,3‐didesoxy‐nono‐2,4‐diuloses4a,band 2‐deoxy‐octo‐1,3‐diuloses4c, respectively. Compound4aand diazomethane react to furnish the correspondi

ISSN:0941-1216    

DOI:10.1002/prac.19983400310

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY

摘要:

AbstractA new synthesis of sodium cyanodithioformate1and the disodium salt ofcis‐1,2‐dicyanoethylene‐1,2‐dithiol2is reported. The key step involves a nucleophilic thiolation with elemental sulfur starting from a substituted acetonitrile4. This method may serve as a cyanide‐ and carbondisulfide‐free alternative in the preparation of the titl

ISSN:0941-1216    

DOI:10.1002/prac.19983400311

出版商:WILEY‐VCH Verlag GmbH    

年代:1998

数据来源: WILEY