Palladium‐Catalyzed Cascade Oligocyclizations Involving Competing Elementary Steps Such as Thermal [1,5]‐Acyl Shifts |
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| Authors: | Wajdi M Tokan Stefan Schweizer Claudia Thies Frank E Meyer Philip J Parsons Armin de Meijere |
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| Institution: | 1. Institut für Organische und Biomolekulare Chemie, Georg‐August‐Universit?t G?ttingen, Tammannstrasse 2, D‐37077 G?ttingen, (fax: +49‐551‐399475);2. Current address: Al‐Balqa' Applied University, As‐salt, Jordan;3. Department of Chemistry, University of Sussex, Brighton, UK |
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| Abstract: | Palladium(Pd)‐catalyzed oligocyclizations of 2‐bromotetradec‐1‐ene‐7,13‐diynes with an unsubstituted terminal acetylene moiety like 3 and 5 and 15‐bromohexadec‐15‐ene‐3,9‐diyn‐2‐ones like 4 and 6 afforded fulvene derivatives 20 and 21 (Scheme 7) and bis(cyclohexane)‐annulated methylenecyclopentene systems 16 and 18 (Schemes 5 and 6), respectively. These transformations constitute cascades of cyclizing carbopalladation steps with ensuing 1,5]‐sigmatropic H‐atom and acyl shifts, respectively (Scheme 8). In contrast, analogous substrates with one three‐atom and one four‐atom tether between the unsaturated C,C‐bonds, such as 1 and 2 , behave differently in that the Pd‐substituted hexa‐1,3,5‐triene intermediates 12 undergo a 6π‐electrocyclization instead of a 5‐exo‐trig carbopalladation followed by β‐hydride elimination to furnish tricyclic bis‐annulated benzene derivatives 13 and 14 (Scheme 4). |
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| Keywords: | Cascade oligocyclizations Palladium complexes Heck‐type carbopalladations [1 5]‐Sigmatropic rearrangement Fulvene derivatives β ‐Hydride elimination |
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