Does Cycloaddition between Pentafulvene and Cyclopentadiene Take Place?

Article abstract of DOI:10.1002/hlca.19900730817

Reaction of a 1:1 mixture of cyclopentadiene (CPD) and pentafulvene (1a) at 20 deg C gives a complex mixture.The low-molecular-weight part mainly consists of pure and mixed dimers (ca. 73percent) besides corresponding trimers (ca. 20percent) 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 1H-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.