Methylated dihydropentafulvalenes and pentafulvalenides from tetramethylcyclopentadiene derivatives

Treatment of tetramethylcyclopentadienyllithium (1Li) with CuCl2 or bromote tramethylcyclopentadiene (4), respectively, as well as reaction of stannyla ted tetramethylcyclopentadiene with 4 in presence of PdBr2 gave two isomeri c octamethyldihydropentafulvalenes (3 and 5), of which 5 was deprotonated t o a highly substituted cyclopentadienyl anion. Conversion of 1Li to iodotet ramethylcyclopentadiene (7) and reaction of 7 with cyclopentadienyl anion y ielded three tautomers of tetramethyldihydropentafulvalene (8a, 8b,and 8c) or exclusively 8a depending on the conditions. The crystal structures of 3 and 8a have been determined, and the isomers of 8 have been converted into the corresponding dianion.