Editing Azulene (section)

==Organic synthesis==
Synthetic routes to azulene have long been of interest because of its unusual structure.<ref>{{cite journal |last1=Gordon |first1=Maxwell |title=The Azulenes |journal=[[Chemical Reviews]] |date=1 February 1952 |volume=50 |issue=1 |pages=127–200 |doi=10.1021/cr60155a004}}</ref> In 1939 the first method was reported by St. Pfau and Plattner <ref>{{Cite journal |doi = 10.1002/hlca.19390220126|title = Zur Kenntnis der flüchtigen Pflanzenstoffe VIII. Synthese des Vetivazulens|journal = [[Helvetica Chimica Acta]]|volume = 22|pages = 202–208|year = 1939|last1 = St. Pfau|first1 = Alexander|last2 = Plattner|first2 = Pl. A.}}</ref> starting from [[indane]] and [[ethyl diazoacetate]].

An efficient [[one-pot synthesis|one-pot]] route entails [[annulation]] of [[cyclopentadiene]] with unsaturated C<sub>5</sub>-[[synthon]]s.<ref>{{cite journal |last1=Hafner |first1=Klaus |last2=Meinhardt |first2=Klaus-Peter | doi= 10.15227/orgsyn.062.0134| title= Azulene| journal=[[Organic Syntheses]] | volume= 62| pages= 134| year= 1984}}</ref> The alternative approach from [[cycloheptatriene]] has long been known, one illustrative method being shown below.<ref>{{Cite journal | doi=10.1002/anie.200501276| pmid=16013070| title=Approach to the Blues: A Highly Flexible Route to the Azulenes| journal=[[Angewandte Chemie International Edition]]| volume=44| issue=32| pages=5130–5133| year=2005| last1=Carret| first1=Sébastien| last2=Blanc| first2=Aurélien| last3=Coquerel| first3=Yoann| last4=Berthod| first4=Mikaël| last5=Greene| first5=Andrew E.| last6=Deprés| first6=Jean-Pierre}}</ref><ref name="Lemal" >{{cite journal |journal=[[Journal of Chemical Education]] |title=Synthesis of azulene, a blue hydrocarbon |volume=65 |issue=10 |year=1988 |page=923 |doi=10.1021/ed065p923|bibcode=1988JChEd..65..923L |last1=Lemal |first1=David M. |last2=Goldman |first2=Glenn D. }}</ref>

[[File:Azulenesynthesis.png|center|720px]]

Procedure:
# [[cycloheptatriene]] 2+2 [[cycloaddition]] with dichloro [[ketene]]
# [[diazomethane]] [[insertion reaction]]
# [[dehydrohalogenation]] reaction with [[dimethylformamide|DMF]]
# [[Luche reduction]] to alcohol with [[sodium borohydride]]
# [[elimination reaction]] with [[Burgess reagent]]
# [[organic oxidation|oxidation]] with [[p-chloranil]]
# [[dehalogenation]] with [[polymethylhydrosiloxane]], [[palladium(II) acetate]], potassium [[phosphate]] and the [[DPDB ligand]]
Another synthesis route starts from the of [[pyridinium]] or [[pyrylium]] salts with [[cyclopentadienyl anion]]:<ref name=":0">{{Cite journal |last1=Shoji |first1=Taku |last2=Ito |first2=Shunji |last3=Yasunami |first3=Masafumi |date=2021-10-01 |title=Synthesis of Azulene Derivatives from 2H-Cyclohepta[b]furan-2-ones as Starting Materials: Their Reactivity and Properties |journal=International Journal of Molecular Sciences |language=en |volume=22 |issue=19 |pages=10686 |doi=10.3390/ijms221910686 |doi-access=free |issn=1422-0067 |pmc=8509482 |pmid=34639027}}</ref>
[[File:Azulene synthesis 1.png|thumb|center]] 
Azulene can also be synthesized via a [[Diels–Alder reaction|Diels Alder]] and [[Retro-Diels–Alder reaction|retro-Diels Alder reaction]]:<ref name=":0" />
[[File:Azulene synthesis 2.png|thumb|center]] 
The starting material of the above reaction can be generated through the [[flash vacuum pyrolysis]] of phenyl propiolate.