The polarity of the carbon-carbon double bond exocyclic to pentafulvenes is a major contributor to the overall dipole moment in monofulvenes. For example, 6, 6- dimethylfulvene, 1, has a dipole moment of 0.44 D.'The exocyclic bond polarizability of pentafulvenes results in ketone-like reactivity. Alkyl-and aryllithium reagents add to the exocyclic carbon-carbon double bond, 2v3 and strong bases