摘要:

AbstractChiral copper(I) and rhodium(II) catalysts designed to achieve enantioselection in cyclopropanation reactions have recently been reported. These catalysts react with diazo compounds to form intermediate metal carbenes that subsequently react with alkenes, in both intermolecular and intramolecular transformations, to form cyclopropane derivatives. They are constructed with chiral ligands whose function is to orient carbene substituents and control olefin approach to the carbenoid center. Enantioselectivities that are greater than 95% have been achieved.In this review, the major advances in chiral catalyst design and development are described, and a uniform mechanistic interpretation is advanced to explain the results accumulated in reported investigations. Focus is placed on chiral salicylaldimine and semicorrin/bis‐oxazoline copper catalysts and on the newest class of chiral catalysts for enantioselective carbenoid reactions, rhodium(II) carboxamides. Although early in their development, sufficient advances have been made to justify placement of this catalytic methodology among the most promising for enantioselective cyclopropanation reaction

ISSN:0165-0513    

DOI:10.1002/recl.19911100702

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractCrystals of 1‐amino‐1‐methylcyclopropane, C4H9N, grown from the liquid, are tetragonal, space groupI41/a, a= 18.142(3),c= 5.882(1) Å, (169K),Z= 16. The finalRfor 733 independent observed reflections is 0.040. The molecule has thes‐transpyramidal conformation for the amino group. The bond‐length asymmetry induced by the substituents is small and about equal to that in aminocyclopropane. The average CC bond length is 1.513 Å (corrected f

ISSN:0165-0513    

DOI:10.1002/recl.19911100703

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe kinetic parameters of the reaction of diphenylcarbodiimide with various carboxylic acids have been determined at a temperature interval of 20‐160°C.The classical scheme for the reaction of carbodiimides with carboxylic acids is extended. It has been found that, at high temperatures, amides and isocyanates are the end products of the reactions.N‐Acylureas, initially formed from aromatic carbodiimides and carboxylic acids, dissociate into isocyanates and amides at temperatures above 60°C.N‐Acylureas formed by the reaction of carboxylic acids with aliphatic carbodiimides prove to be more stable: their dissociation temperature is about 50°C higher. Both the formation and dissociation ofN‐acylureas are much faster when the parent acid i

ISSN:0165-0513    

DOI:10.1002/recl.19911100704

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractSulfurization of protected [i.e., 2‐cyanoethyl, methyl and 2‐(4‐nitrophenyl)ethyl] internucleosidic phosphite triesters can be conveniently executed with the easily accessible reagent, phenylacetyl disulfide (1). High‐quality oligodeoxynucleotides containing predetermined combinations of natural and phosphorothioate linkages can be obtained via a solid‐phase approach by using reagent 1 and 2‐(4‐nitrophenyl)ethyl‐protected p

ISSN:0165-0513    

DOI:10.1002/recl.19911100705

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe high‐yield synthesis of four mono‐ and one dideutero‐labelled spheroidene, the carotenoid bound in the reaction centre ofRhodobacter sphaeroides 2.4.1, is described. The all‐Eisomers (14′‐2H)‐, (15′‐2H)‐, (15‐2H), (14‐2H)‐ and (15,15′‐2H2)spheroidenes have been prepared in high purity with more than 95%2H incorporation from C2H3CN and/or Dibal‐2H. The spectroscopic properties of the labelled compounds are discussed; the mass spectra reveal that toluene elimination from spheroidene is restricted to a

ISSN:0165-0513    

DOI:10.1002/recl.19911100706

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractConversion of dilute aqueous solutions of 5‐hydroxymethyl‐2‐furaldehyde and D‐fructose under near‐critical conditions led to the formation of 1,2,4‐benzenetriol in relatively

ISSN:0165-0513    

DOI:10.1002/recl.19911100707

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractElectrochemical oxidation of [Bu4N][Ni(dmise)2] in the presence of Me4NPF6yields [Me4N][Ni(dmise)2]2, the selenone derivative of the superconducting [Me4N][Ni(dmit)2]2. The X‐ray structure of [Me4N][Ni(dmise)2]2reveals a non‐stacking arrangement of paired anions. The [Ni(dmise)2]2diads are connected along thec‐axis via a short intermolecular Se…Se contact of 3.277(3) Å. Preliminary conductivity measurements show a room temperature conductivity of 20 S cm−1with a metallic behavior down to 140 K, at which point a metalinsulator transit

ISSN:0165-0513    

DOI:10.1002/recl.19911100708

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractPhosphorus oxychloride is described as a condensing agent in the preparation of nitroanilides. The condensation was free of racemization with amino acid derivatives of the urethane type and the current amino protective groups can be applied. The yields are high to excellent.

ISSN:0165-0513    

DOI:10.1002/recl.19911100709

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

摘要:

AbstractThe fluorescence of the C70fullerene chromophore in three solvents is reported. Quenching of this fluorescence by organic electron donors occurs as a result of photoinduced electron transfer. With aniline‐type donors ground‐state charge transfer complex formation is evident from curved Stern‐Volmer plots as well as from additional long wavelength absor

ISSN:0165-0513    

DOI:10.1002/recl.19911100710

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY

ISSN:0165-0513    

DOI:10.1002/recl.19911100712

出版商:WILEY‐VCH Verlag    

年代:1991

数据来源: WILEY