(Download) "Combined Coinage Metal Catalysis for the Synthesis of Bioactive Molecules (Report)" by Norbert Aksin-Artok, Ozge Breker, Viola Deutsch, Carl Gockel, Birgit Poonoth, Manojkumar Sawama, Yoshinari Sawama, Yuka Sun, Tao Winter, Christian Krause ~ Book PDF Kindle ePub Free

eBook details

Title: Combined Coinage Metal Catalysis for the Synthesis of Bioactive Molecules (Report)
Author : Norbert Aksin-Artok, Ozge Breker, Viola Deutsch, Carl Gockel, Birgit Poonoth, Manojkumar Sawama, Yoshinari Sawama, Yuka Sun, Tao Winter, Christian Krause
Release Date : January 01, 2010
Genre: Chemistry,Books,Science & Nature,Professional & Technical,Engineering,
Pages : * pages
Size : 85 KB

Description

The coinage metals copper, silver, and gold belong to the seven metals of alchemy. They have been known to mankind for thousands of years, and gold may have been the first metal ever used by humans [1]. Whereas copper enjoys a rich history in organometallic chemistry and organic synthesis, starting with contributions by Kharasch and Gilman in the 1940s and 1950s [1,2], the usage of silver and gold in transition-metal catalysis commenced much more recently. In our research program, we find it particularly interesting to combine the (quite different) reactivities of the coinage metals in the stereo-selective synthesis of bioactive target molecules [3]. Functionalized allenes are ideal substrates for these transformations since they are not only very reactive [4], but also inherently chiral [5]. Copper is the transition element of choice for the synthesis of functionalized allenes by [S.sub.N]2'-substitution of propargyl electrophiles. Whereas various carbon nucleophiles can be introduced by this method, either using stoichiometric cuprates or copper catalysis together with Grignard reagents [6], the smallest nucleophile--the hydride ion--has so far only played a minor role in this chemistry. Recently, we have established a copper-catalyzed [S.sub.N]2'-reduction of propargyl oxiranes 1 which provides an efficient route to [alpha]-hydroxyallenes of the type 2 (Scheme 1) [7]. Key to success is the stabilization of the catalytically active copper hydride species (formed in situ from CuCl and the stoichiometric hydride source polymethylhydridosiloxane [PMHS]) by an N-heterocyclic carbene (e.g., IBiox7). This transformation proceeds with high anti-stereoselectivity by center-to-axis chirality transfer and is compatible with various functional groups (alcohols, esters, ethers, etc.). Extension to propargyl carbonates [8] has broadened the range of allenes available by the method and offers advantages with respect to stereo-selectivity and substrate reactivity.