View source for Aza-crown ether

{{short description|Ring molecule with several amine (–N– or >N–) groups}}
[[File:Co((CH2CH2NH)6)+++(BIGNOU01).png|thumb|The structure of {{chem2|[Co(III)(CH2CH2NH)6](3+)}}.<ref>{{cite journal |doi=10.1107/S0108768192002714|title=Electron-density distribution in crystals of 1,4,7,10,13,16-hexaazacyclooctadecanecobalt(III) trichloride, meso-&#91;Co(hexaen)&#93;Cl3 at 106 K|year=1992|last1=Morooka|first1=M.|last2=Ohba|first2=S.|last3=Toriumi|first3=K.|journal=Acta Crystallographica Section B: Structural Science|volume=48|issue=4|pages=459–463}}</ref>  Color code: blue = N, gray = C, black = C, white = H.]]
In [[organic chemistry]], an '''aza-crown ether''' is an aza [[Structural analog|analogue]] of a [[crown ether]] (cyclic polyether).<ref>{{cite journal |doi=10.1016/S0010-8545(98)00243-4|title=Proton coordination by polyamine compounds in aqueous solution|year=1999|last1=Bencini|first1=Andrea|last2=Bianchi|first2=Antonio|last3=Garcia-España|first3=Enrique|last4=Micheloni|first4=Mauro|last5=Ramirez|first5=José Antonio|journal=Coordination Chemistry Reviews|volume=188|pages=97–156}}</ref><ref>{{cite journal |doi=10.1039/b106367g|title=Metal complexes of azacrown ethers in molecular recognition and catalysis|year=2002|last1=Reichenbach-Klinke|first1=Roland|last2=König|first2=Burkhard|journal=Journal of the Chemical Society, Dalton Transactions|issue=2|pages=121–130}}</ref> That is, it has a [[nitrogen]] atom ([[amine]] linkage, {{chem2|\sNH\s}} or {{chem2|>N\s}}) in place of each [[oxygen]] atom ([[ether]] linkage, {{chem2|\sO\s}}) around the [[Ring (chemistry)|ring]]. While the [[Parent structure|parent]] crown ethers have the formulae {{chem2|(CH2CH2O)_{''n''} }}, the parent ''aza''-crown ethers have the formulae {{chem2|(CH2CH2NH)_{''n''} }}, where n = 3, 4, 5, 6.  Well-studied aza crowns include [[triazacyclononane]] (n = 3), [[cyclen]] (n = 4),<ref>{{cite journal|journal=Org. Synth. | title = 1,4,7,10-Tetraazacyclododecane | first1= David P.|last1= Reed |first2=Gary R. |last2=Weisman | volume = 78 | pages = 73 | year = 2002 | doi =  10.15227/orgsyn.078.0073}}</ref> and [[hexaaza-18-crown-6]] (n = 6).<ref name = atkins/>
<gallery caption="Selected aza-crowns and their complexes"center >
File:Me3TACN.png|[[1,4,7-Trimethyl-1,4,7-triazacyclononane]], a tridentate ligand used in [[coordination chemistry]].
File:Cyclam.png|[[Cyclam]] is a tetraaza crown ether with alternating {{chem2|(CH2)2}} and {{chem2|(CH2)3}} linkers between amine centers.
File:Plerixafor.svg|[[Plerixafor]], a derivative of cyclam, is used to treat [[lymphoma]] and [[multiple myeloma]].<ref name="DrugsRD">{{Cite journal | title = Plerixafor | journal = Drugs in R&D | volume = 8 | issue = 2| pages = 113–119 | year = 2007 | doi = 10.2165/00126839-200708020-00006| pmid = 17324009 | last1 = <!-- --> }}</ref>
File:Cryptand.svg| [[2.2.2-Cryptand]] is an aza-crown of the mixed ether-amine variety.
</gallery>
==Synthesis==
The synthesis of aza crown ethers are subject to the challenges associated with the preparation of [[macrocycle]]s.<ref>{{cite journal |doi=10.1021/cr00094a008|title=Synthesis of aza-crown ethers|year=1989|last1=Krakowiak|first1=Krzysztof E.|last2=Bradshaw|first2=Jerald S.|last3=Zamecka-Krakowiak|first3=Daria J.|journal=Chemical Reviews|volume=89|issue=4|pages=929–972}}</ref> The 18-membered ring in (CH<sub>2</sub>CH<sub>2</sub>NH)<sub>6</sub> can be synthesized by combining two triamine components.<ref name = atkins>{{cite journal|journal=Org. Synth. | title = 1,4,7,10,13,16-Hexaazacyclooctadecane | first1= T. J.|last1= Atkins|first2= J. E.|last2= Richman|first3= W. F.|last3= Oettle | volume = 58 | page = 86 | year = 1978 | doi = 10.15227/orgsyn.058.0086}}</ref>  By reaction with [[tosyl chloride]], [[diethylene triamine]] is converted to a derivative with two secondary [[sulfonamide]]s.  This compound serves as a building block for [[macrocyclization]]s.
==Variants==
Many kinds of aza crown ethers exist.
;Variable length linkers
Aza crowns often feature trimethylene ((CH<sub>2</sub>)<sub>3</sub>) as well as ethylene ((CH<sub>2</sub>)<sub>2</sub>) linkages. One example is [[cyclam]] (1,4,8,11-tetraazacyclotetradecane).
;Tertiary amines
In many aza-crown ethers some or all of the amines are tertiary. One example is the tri([[tertiary amine]]) (CH<sub>2</sub>CH<sub>2</sub>NCH<sub>3</sub>)<sub>3</sub>, known as [[trimethyltriazacyclononane]]. [[Cryptand]]s, three-dimensional aza crowns, feature tertiary amines.
;Mixed ether-amine ligands
Another large class of macrocyclic ligands feature ''both'' ether and amines.<!--33941-15-0-->.<ref>{{cite journal |doi=10.1021/ja00732a007|title=Stability constants of cyclic polyether complexes with univalent cations|year=1971|last1=Frensdorff|first1=Hans K.|journal=Journal of the American Chemical Society|volume=93|issue=3|pages=600–606}}</ref> One example is the diaza-18-crown-6, [(CH<sub>2</sub>CH<sub>2</sub>O)<sub>2</sub>(CH<sub>2</sub>CH<sub>2</sub>NH)]<sub>2</sub>.<ref>{{cite journal |journal=Organic Syntheses| first1= Vincent J.|last1= Gatto|first2= Steven R.|last2= Miller|first3= George W.|last3= Gokel | title = 4,13-Diaza-18-Crown-6 | volume = 68 | pages = 227| year = 1990 | doi = 10.15227/orgsyn.068.0227}}</ref>
;Lariate crowns
The presence of the amine allows the formation of [[Lariat]] crown ethers, which feature sidearms that augment complexation of cation.<ref>{{cite journal|first1=G. W.|last1= Gokel|first2= L. J. |last2=Barbour|first3= R. |last3=Ferdani |first4=J.|last4= Hu |title=Lariat Ether Receptor Systems Show Experimental Evidence for Alkali Metal Cation Interactions|journal=Acc. Chem. Res. |year=2002 |volume=35|issue= 10|pages= 878–886 |doi=10.1021/ar000093p|pmid= 12379140}}</ref>
==References==
<references />
[[Category:Polyamines]]
[[Category:Secondary amines]]
[[Category:Tertiary amines]]
[[Category:Ethyleneamines]]
[[Category:Chelating agents]]
[[Category:Macrocycles]]