Palladium‐Catalyzed Cascade Oligocyclizations Involving Competing Elementary Steps Such as Thermal [1,5]‐Acyl Shifts

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 6 π ‐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 ).