title: Fulvenes
text: # Fulvenes
  
  Fulvenes are the class of hydrocarbon obtained by formally cross-conjugating one ring and methylidene through a common exocyclic double bond.
  
  The name is derived from fulvene, which has one pentagonal ring. Other examples include methylenecyclopropene (triafulvene) and heptafulvene.
  
  ## Subclasses
  
  Several types of fulvenes are defined. They are:
  
  * triafulvene
  * pentafulvene
  * heptafulvene
  * nonafulvene
  
  ## Preparation
  
  Fulvenes are readily prepared by the condensation of cyclopentadiene and aldehydes and ketones:
  
      $C_5H_6$ + $R_2C=O$ → $C_4H_4C=CR_2$ + $H_2O$
  
  Thiele is credited with discovering this reaction.
  
  Modern synthesis of fulvenes employ buffer systems.
  
  ## Ligand in organometallic chemistry
  
  Fulvenes are common ligands and ligand precursors in organometallic chemistry. 2,3,4,5-Tetramethylfulvene, abbreviated $Me_4Fv,$ results from the deprotonation of cationic pentamethylcyclopentadienyl complexes. Some $Me_4Fv$ complexes are called tuck-in complexes.
  
  