Aza-crown ether

In organic chemistry, an aza-crown ether is an aza analogue of a crown ether. That is, it has a nitrogen atom in place of each oxygen atom around the ring. While the parent crown ethers have the formulae, the parent aza-crown ethers have the formulae, where n = 3, 4, 5, 6. Well-studied aza crowns include triazacyclononane, cyclen, and hexaaza-18-crown-6.

Synthesis

The synthesis of aza crown ethers are subject to the challenges associated with the preparation of macrocycles. The 18-membered ring in ₆ can be synthesized by combining two triamine components. By reaction with tosyl chloride, diethylene triamine is converted to a derivative with two secondary sulfonamides. This compound serves as a building block for macrocyclizations.

Variants

Many kinds of aza crown ethers exist.
;Variable length linkers: Aza crowns often feature trimethylene as well as ethylene linkages. One example is cyclam.
;Tertiary amines: In many aza-crown ethers some or all of the amines are tertiary. One example is the tri ₃, known as trimethyltriazacyclononane. Cryptands, three-dimensional aza crowns, feature tertiary amines.
;Mixed ether-amine ligands: Another large class of macrocyclic ligands feature both ether and amines. One example is the diaza-18-crown-6, ₂.
;Lariat crowns: The presence of the amine allows the formation of Lariat crown ethers, which feature sidearms that augment complexation of cation.