Coronand, subunit

The structure of the coronand subunit, including the e/ido-selectiv-ity of these double Diels-Alder adducts, has been elegantly demonstrated in model reactions. The orientation of the unsymmetrical... 

Myriad polydentate aza-macrocycles have been reported 41. The extent of the subject forces limitation of this discussion to only macrocycles containing a pyridine or dipyridine subunit. Most of these coronands have been synthesized by a SchifF base condensation of an aldehyde or ketone with a hfc-primary amine in the presence of a metal ion. The metal ion acts as a template, resulting in dramatic increases in yield of the desired cyclic product over linear polymerization products42 46. Lindoy and Busch45 have described this effect in two ways, kinetic and thermodynamic. If the metal ion controls the steric course of a series of stepwise reactions, the template effect is considered to be kinetic. If the metal ion influences an equilibrium in an organic reaction sequence by coordination with one of the reactants, the template effect is termed thermodynamic. It is the kinetic effect that is believed to be operative in most metal ion-assisted (in situ) syntheses of... 

As with the aza coronands previously discussed, the majority of the coronands containing oxygen and nitrogen have been synthesized by Schiff base condensation or via a nucleophilic substitution of a halide on a compound processing either pyridine or dipyridine subunits. 

This discussion has covered all the coronands synthesized to date which contain nitrogen and oxygen heteroatoms or strictly nitrogen atoms in addition to a pyridino subunit in the macrocyclic framework. It has also included a discussion of any... 

Klemm and co-workers have applied this double Diels-Alder methodology to the synthesis of novel polymers. Copolymerization of bispyrone 23 with bismaleimide 24 leads to soluble, stable polymers of number-average molecular weights between 10,000 and 34,000. The polymers are composed of coronand structure subunits 25 alternating with alkyl linkers. 

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