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131.
132.
John M. Brown 《Angewandte Chemie (International ed. in English)》1987,26(3):190-203
Stereochemical control is a major concern in the application of homogeneous catalysis to organic chemistry. In this context, the directed hydrogenation of olefins employing cationic rhodium or iridium catalysts has considerable potential, for very high selectivity can be attained under mild reaction conditions. The only requirement is a polar functional group in proximity to the double-bond which remains bound to the metal during the catalytic cycle and thereby controls the Stereochemical course of hydrogen delivery through the constraints of chelation. The substituent is most frequently a hydroxy group OH but can also be an ester, amide or carbamate group; other groups remain to be scrutinized. In cyclic compounds, directed hydrogenation can lead to face-selectivity, and the polar substituent may be in the β-, γ-, or δ-position to the double-bond. Acyclic stereoselection ensues with β- or γ-substituents in appropriate compounds, and the configuration of reduced product is predictable on the basis of simple rules. The application of optically active rhodium complexes leads to useful kinetic resolution procedures. 相似文献
133.
Alois Fürstner 《Angewandte Chemie (International ed. in English)》1993,32(2):164-189
Today, the synthetic chemist has a large repertoire of metal activation methods at his disposal. After a first breakthrough was made at the beginning of the seventies with the introduction of the Rieke metals, a series of further, in part more efficient methods were describes, based on which not only classical metal-induced reactions could be substantially improved but also completely new reactions could be discovered. In this article the individual activation methods are discussed and compared as far as is possible using the currently available data. Especially noteworthy are the metal–graphite combinations because of their unsurpassed reactivity and concomitant easy preparation and manipulation. As shown by numerous applications of these reagents on polyfunctional substrates, particularly natural products, high reactivity of the metal and excellent selectivity are by no means precluded. Besides the purely preparative aspects also insights gained so far into the general principles and limits of metal activation are outlined, and attempts at determining the morphology of highly dispersed systems are reported. 相似文献
134.
咪唑环合成方法的新进展 总被引:7,自引:0,他引:7
综述了咪唑环合成方法的新进展,讨论了部分合成方法的特点及反应机理。参考文献41篇。 相似文献
135.
136.
G. Tuchscherer 《Tetrahedron letters》1993,34(52):8419-8422
A chemoselective ligation via oxime bond formation is used for the chemical synthesis of template assembled peptides according to the TASP (Template Assembled Synthetic Proteins) approach. Aminooxyacetylation of the multifunctional partial sequence Lys- Arg- Asp- Ser of lactoferrin and subsequent condensation in aqueous solution with a topological template containing four selectively addressable aldehyde functions as attachment sites gives readily access to the TASP molecule. 相似文献
137.
138.
With the aid of selected examples an overview is given of the development trends in highly discriminative reactions using organoaluminum compounds. (1) Isomerization of substituted oxiranes into allyl alcohols has been effected both stereo- and regioselectively by means of a new organoaluminum reagent, diethylaluminum 2,2,6,6-tetramethylpiperidide (DATMP); this reaction which provides a new route for the regiospecific transformation of allyl alcohols into 1,3-dienes. (2) A novel nonenzymic heterolysis of allylic phosphates of terpenoids has been effected by organoaluminum compounds and has enabled development of a new method for the selective synthesis of cyclic terpenes. (3) The reductive condensation of α-haloketones with carbonyl compounds in the presence of diethylaluminum chloride and zinc affords β-hydroxy-carbonyl derivatives in good yields with exclusion of undesired self-condensations products. 相似文献
139.
140.
Methods for the preparation of thiocarboxamides are described with special reference to progress achieved in the last few years. The discussion is arranged according to the eight most important reaction types. 相似文献