Norbornadiene

Norbornadiene is a bicyclic hydrocarbon. The molecule can be envisioned as a 1,4-cyclohexadiene bridged in the para positions by a methylene group. The compound is related to norbornene in which one of the double bonds is saturated. Norbornadiene and related compounds are of great scientific interest because of the unusual geometry and high reactivity.

Synthesis
The norbornadiene framework is based on a Diels-Alder reaction between a cyclopentadiene and an alkyne.


 * [[Image:Norbornadiene synthesis.gif|left|Norbornadiene synthesis]]

Reactions
Quadricyclane is a norbornadiene isomer. It can be obtained from norbornadiene by a photochemical reaction when assisted by a sensitizer such as acetophenone. The norbornadiene quadricyclane couple is of potential interest for solar energy storage when controlled release of the strain energy stored in quadricyclane back to norbornadiene is made possible.1 Quadricyclane is very reactive towards dienophiles in cycloaddition reactions.

Norbornadienes also form organometallic sandwich compounds such as tetracarbonyl(norbornadiene)chromium(0)..3 This complex is a useful reagent which transfers chromium tetracarbonyl to bidentate phosphine ligands.


 * [[Image:Quadricyclane.gif|left|quadricyclane]]

Norbornadiene is also the starting material for the synthesis of diamantane and sumanene and it is used as an acetylene transfer agent for instance in reaction with 3,6-di-2-pyridyl-1,2,4,5-tetrazine.2

Quadricyclane is also highly toxic.4