Katalytische selektive Synthese

Abstract

Der Verlauf und das Produkt einer Reaktion lassen sich gezielt über die Katalysatorstruktur steuern, selbst bei nahezu identischen Reaktionsbedingungen. Katalysatorkontrollierte Selektivität ist in der enantioselektiven Synthese gut etabliert, in katalytischen regio‐, chemo‐ und produktselektiven Reaktionen aber wenig verbreitet. Dieser Aufsatz beschreibt, wie eine Ausgangsverbindung lediglich durch die Auswahl des Katalysators selektiv in zwei oder mehr unterschiedliche Produkte umgewandelt werden kann. Wir stellen Beispiele selektiver Katalysen vor und hoffen, dass die bisher erzielten Fortschritte ermutigend für das Gebiet sind. Zugleich wollen auch die noch offenen Fragen beim Entwurf und dem mechanistischen Verständnis selektiver Katalysatoren thematisieren.

Catalytic Asymmetric Diels–Alder Reaction of Quinone Imine Ketals: A Site‐Divergent Approach

“…[9,10] However, using catalyst control to overturn the inherent siteselectivity of as ubstrate is still ac hallenging task. [9,10] However, using catalyst control to overturn the inherent siteselectivity of as ubstrate is still ac hallenging task.…”

“…This study led us to establish ah ighly enantioselective Diels-Alder reaction between av ariety of 3-alkyl quinone imine ketals and diene carbamates catalyzed by axially chiral dicarboxylic acids (R)-1 ( Figure 1c). [9,10] This counter-intuitive selectivity will be explained by considering the E/Z isomerization of the imino functionality which acts as af luxional directing group. This site-divergent strategy enabled the synthesis of cycloadducts having an all-carbon quaternary stereocenter while leaving the lesshindered C = Cb ond for later transformation.…”

Divergent C–H Annulation for Multifused N‐Heterocycles: Regio‐ and Stereospecific Cyclizations of N‐Alkynylindoles

“…[4b,c] Recently,i tw as found that fused aromatic systems bearing internal nitrogen, such as azacorannulene [5] and azafullerenes, [6] have shown interesting electronic and optical properties in energy conversion applications.F or the synthesis of fused N-heterocycles,d ivergent reactions would be ideal if controlled stereospecifically,chemospecifically,and regiospecifically from common starting materials. [7] Further, cyclo-isomerization is aversatile strategy for creating cyclic organic compounds from acyclic starting materials in an atomeconomical manner. [8] If possible,asimultaneous multiple ring fusion will be highly desirable for more complex molecules.…”

“…[15] However,i ntramolecular baddition of aryl groups to ynamine is unprecedented to the best of our knowledge [10a] and these cycloisomerizations occurred regardless of the electronic nature of the C2phenyl ring due to the high reactivity of ynamine.I nterestingly,w hen PdCl 2 was used with external oxidant, [16] ac yclodimerized product 4 was obtained. Alternatively,t he synthesis of as imple benzo [7,8]indolizino[2,3,4,5-ija]quinoline 8 was demonstrated through alkyne addition and sequential double cyclization.…”

Asymmetric γ‐Allylation of α,β‐Unsaturated Aldehydes by Combined Organocatalysis and Transition‐Metal Catalysis

“…[1] Even though the development of catalytic approaches has allowed tremendous progress in the ability to form products in as elective fashion, the ability to access the full array of isomers in ad ivergent fashion remains ac hallenge.F or transition-metal-catalyzed allylic alkylation of nucleophiles,areaction which represents one of the fundamental carbon-carbon and carbon-heteroatom bond-forming reactions (Figure 1a), the most important selectivity issues are the control of regio-and stereoselectivity.I nt he last decades,r emarkable progress has been made in the area of stereoselective allylations of nucleophiles and alarge number of asymmetric versions have been disclosed. In the last decades,catalysis has been established as the stateof-the-art method for performing reactions in an efficient and selective manner.…”