Editing Diene (section)

== Reactivity and uses==

===Polymerization===
The most heavily practiced reaction of alkenes, dienes included, is [[polymerization]].  1,3-Butadiene is a precursor to [[Synthetic rubber|rubber]] used in tires, and [[isoprene]] is the precursor to [[natural rubber]].  [[Chloroprene]] is related but it is a synthetic monomer.

===Cycloadditions===
An important reaction for conjugated dienes is the [[Diels–Alder reaction]].  Many specialized dienes have been developed to exploit this reactivity for the synthesis of [[natural product]]s (e.g., [[Danishefsky's diene]]).

===Other addition reactions===
Conjugated dienes add reagents such as [[bromine]] and [[hydrogen]] by both 1,2-addition and 1,4-addition pathways.  Addition of polar reagents can generate complex architectures:<ref>{{OrgSynth | author = Roger Bishop | collvol = 9 | collvolpages = 692 | prep = CV9P0692
| title =9-Thiabicyclo[3.3.1]nonane-2,6-dione}}{{cite journal | title =2,6-Dichloro-9-thiabicyclo[3.3.1]nonane: Multigram Display of Azide and Cyanide Components on a Versatile Scaffold | first4 = M. G. | last4 = Finn | first3 = K. Barry | last3 = Sharpless | journal = [[Molecules (journal)|Molecules]] | first2 = Antonella | year = 2006 | volume = 11 | last2 = Converso | pages = 212–218 | doi = 10.3390/11040212 | author = Díaz, David Díaz | issue = 4| pmid = 17962753 | pmc = 6148556 | doi-access = free }}</ref>
::[[Image:CODSCl2.png|450px|2,6-Dichloro-9-thiabicyclo[3.3.1]nonane, synthesis and reactions]]

===Metathesis reactions===
Nonconjugated dienes are substrates for [[ring-closing metathesis]] reactions.  These reactions require a metal [[catalyst]]:
::[[File:RCM cyclophane example.png|520px]]

===Acidity===
The position adjacent to a double bond is [[acid]]ic because the resulting [[allyl]] anion is stabilized by resonance. This effect becomes more pronounced as more alkenes are involved to create greater stability. For example, deprotonation at position 3 of a 1,4-diene or position 5 of a 1,3-diene give a [[pentadienyl]] anion. An even greater effect is seen if the anion is aromatic, for example, deprotonation of [[cyclopentadiene]] to give the [[cyclopentadienyl anion]].<!-- TODO: chart of pKa for methylene in alkane, singly and doubly allylic, and Cp -->

[[File:HayashiChiralNBD.svg|thumb|left|122px|[[C2-Symmetric ligands|C<sub>2</sub>-symmetric]] diene ligand used in [[asymmetric catalysis]].<ref>{{cite journal|vauthors=Hayashi T, Ueyama K, Tokunaga N, Yoshida K|title=A Chiral Chelating Diene as a New Type of Chiral Ligand for Transition Metal Catalysts: Its Preparation and Use for the Rhodium-Catalyzed Asymmetric 1,4-Addition|journal=J. Am. Chem. Soc.|year=2003|volume=125|issue=38|pages=11508–11509|doi=10.1021/ja037367z|pmid=13129348}}</ref>]]

===As ligands===
Dienes are widely used chelating [[ligand]]s in [[organometallic chemistry]].  In some cases they serve as placeholder ligands, being removed during a catalytic cycle.  For example, the cyclooctadiene ("cod") ligands in [[bis(cyclooctadiene)nickel(0)]] are labile.  In some cases, dienes are spectator ligands, remaining coordinated throughout a catalytic cycle and influencing the product distributions.  [[Chirality|Chiral]] dienes have also been described.<ref>{{Cite journal |last1=Huang |first1=Yinhua |last2=Hayashi |first2=Tamio |date=2022-09-28 |title=Chiral Diene Ligands in Asymmetric Catalysis |url=https://pubs.acs.org/doi/10.1021/acs.chemrev.2c00218 |journal=Chemical Reviews |language=en |volume=122 |issue=18 |pages=14346–14404 |doi=10.1021/acs.chemrev.2c00218 |issn=0009-2665 |pmid= 35972018}}</ref>  Other diene complexes include [[(Butadiene)iron tricarbonyl|(butadiene)iron tricarbonyl]], [[cyclobutadieneiron tricarbonyl]], and [[cyclooctadiene rhodium chloride dimer]].