Fulvenes
# 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.

