Bilden sich aus Pentafulven und Cyclopentadien [6+4]‐Cycloaddukte??

Does [6+4] Cycloaddition between Pentafulvene and Cyclopentadiene Take Place? Reaction of a 1:1 mixture of cyclopentadiene (CPD) and pentafulvene ( 1a ) at 20° gives a complex mixture. The low‐molecular‐weight part mainly consists of pure and mixed dimers ( ca. 73 %) besides corresponding trimers ( ca. 20%) and some corresponding oligomers according to GC/MS investigations ( Fig. 1 ). The 3 predominant ‘mixed dimers’ between CPD and 1a have been separated, and structures 4 – 6 ( Scheme 3 ) are assigned according to 400‐ and 600‐MHz 1 H‐NMR investigations. These results show that HOMO(CPD)‐LUMO(fulvene) interactions are important in pentafulvene cycloadditions. Dimer 6 results from [6+4] cycloaddition followed by [1,5]‐H shifts.