macrocycle

class=skin-invert-image|thumb|240px|Erythromycin, a [[macrolide antibiotic, is one of many naturally occurring macrocycles.]] Macrocycles are often described as molecules and ions containing a ring of twelve or more atoms. Classical examples include the crown ethers, calixarenes, porphyrins, and cyclodextrins. Macrocycles describe a large, mature area of chemistry.

== Synthesis == The formation of macrocycles by ring-closure is called macrocyclization. The central challenge to macrocyclization is that few bond-forming reactions give large rings. Instead, medium sized rings or polymers tend to form. Early macrocyclizations were achieved ketonic decarboxylations for the preparation of terpenoid macrocycles. So, while Ružička was able to produce various macrocycles, the yields were low. This kinetic problem can be addressed by using high-dilution reactions, whereby intramolecular processes are favored relative to polymerizations. Reactions amenable to high dilution include Dieckmann condensation and related based-induced reactions of esters with remote halides. High dilution ring-closing metathesis (1mg/1mL solvent) was used to prepare muscone in 76% yield. class=skin-invert-image|550px|left|Synthesis of muscone via high dilution RCM