Fulvenes, fulvalenes, part 72. Exploring a new general pathway to parent hydrocarbons heptafulvene, heptapentafulvalene, and heptafulvalene

A new general pathway to the parent cross-conjugated hydrocarbons heptafulv ene (1) (Scheme 3), sesquifulvalene (2) (Scheme 4), and heptafulvalene (3) (Scheme 5 has been explored, starting with essay available 7,7-dibromobicyc lo[4.1.0]hept-3-ene (13). Promising precursors have been synthesized by hal o/lithio exchange of 1,1-dibromocyclopropane 13 --> 14, followed by methyla tion (--> 1), cyclopentadienylation (-->2) and CuCI2-induced 'carbene dimer ization' (--> 3) of the carbenoid 14 So far the main obstacle of all three sequences (cf: Schemes 3, 4, and 5) is the final base-induced dehydrobromin ation of precursors 17, 24 and 27, which should be investigated in more det ail.