Synthesis of oxacalixarenes incorporating nitrogen heterocycles: evidence for thermodynamic control.

[structure: see text] Oxacalix[2]arene[2]hetarenes are formed in a single step by cyclooligomerization of meta-diphenols with meta-dichlorinated azaheterocycles. The high selectivity for cyclic tetramer formation results from thermodynamic product control. Macrocycles as large as oxacalix[5]arene[5]hetarenes have been isolated under nonequilibrating conditions.