The preparation and utilization of specific biaryl systems, particularly those which suffer hindered rotation, is a demanding goal not only in the synthesis of natural products and pharmaceuticals, but also for example in the discovery of new reagents for asymmetric synthesis. This article will attempt to provide a topical review of modern, efficient processes for the specific preparation of biaryls. This appears to be of particular urgency, since, under the pressure of continually increasing demand, a wealth of new or modified synthetic approaches to the ever more important biaryl systems has been realized in recent years. The high standard which has been reached in this field is impressively demonstrated by regio-and stereoselective syntheses of important biaryl natural products such as steganone, ancistrocladine, ancistrocladisine, and dioncophylline A. Besides the utilization of asymmetric induction in the actual coupling step, the thermodynamically or kinetically controlled torsion of biaryl axes belongs to the most important concepts discussed.
The practicable synthesis of all imaginable isomeric heterocyclic moieties 8-11 and ent-8-ent-11 of the naphthylisoquinoline alkaloids is described. The stereoinformation at C-3 is induced by asymmetric reductive amination, using 1-phenylethylamines of either enantiomeric series as chiral auxiliaries. The key step of the stereocontrolled construction of the stereocenter at C-1 is the diastereoselective reduction of the corresponding dihydroisoquinolines, as obtained by Bischler-Napieralski synthesis, or the regio-and stereoselective Pictet-Spengler reaction of arylisopropylamines with acetaldehyde, respectively.
Die präparative Bereitstellung insbesondere rotationsgehinderter Biarylsysteme ist ein anspruchsvolles Ziel nicht nur in der Natur‐ und Wirkstoffsynthese, sondern z. B. auch bei der Erschließung neuer Reagentien für die asymmetrische Synthese. Dieser Aufsatz gibt eine aktuelle Übersicht über moderne, leistungsfähige Verfahren zum gezielten Aufbau von Biarylen. Dies scheint besonders dringlich, weil in den letzten Jahren eine Fülle neuer oder modifizierter Zugänge zu den immer wichtiger werdenden Biarylsystemen erarbeitet worden ist. Der inzwischen erreichte Standard spiegelt sich eindrucksvoll in kürzlich publizierten regio‐ und stereoselektiven Synthesen wichtiger Biarylnaturstoffe wider, darunter Steganon, Ancistrocladin, Ancistrocladisin und Dioncophyllin A. Zu den wichtigsten Konzepten zählt dabei neben der Nutzung asymmetrischer Induktion im eigentlichen Kupplungsschritt neuerdings auch die thermodynamisch oder kinetisch kontrollierte Verdrillung von Biarylachsen.
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