Heterocalixarenes

Molecules related to calixarenes may also form hydrogen bonded network structures. The heterocalixarene (calix[l]benzimidazol-2-one[2]arene) 17 forms... 

S. Kumar, N. Kaur, and H. Singh (Guru Nanak Dev University, Amritsar, India) have followed up their review entitled Syntheses, Structures and Interactions of Heterocalixarenes in Volume 89 of Advances in Heterocyclic Chemistry with a new consideration of metallacalixarenes and their organo-inorganic hybrid molecular architectures. 

An appealing combination of a calixarene with the corresponding calrxpyrrole (a heterocalixarene ) was realized with compounds 111, which were synthesized by condensation of the 2-oxopropyl ethers with pyrrole in 32% and 10% yield, respectivel)f . ... 

The tetranuclear metal complex, [(l,2-diaminoethane)Pt(uracilate-AM,A(3)] , can be considered a special heterocalixarene, a metal analogue of calix[4]arene which functions as hosts for small molecules or ions and possesses metal binding properties, either in the cavity or at the periphery. The bridging unit of the classical calix[4]arene, usually a CH2 group, is replaced by the (en)Pt(II) unit in the Pt-complex. This change, the replacement of the p-phenol by the 2,4-dioxopyrimidine and the positive charge introduced by the metal cations, leads to a number of differences as compared with the classical calix[4]arenes. Their preparation, x-ray crystal structure, and solution behavior have been described <94JA616>. 

These heterocalixarenes possessing unusually crowded cavities with 3 or 4 nitrogen electron lone pairs and having all sp carbons are expected to be essentially planar. But in its X-ray structure, 89 is distinctly non-planar, due predominantly to lone pair-lone pair repulsions. The distortion from planarity leads to a conformation in which two lone pairs tip out of plane on one side of the molecule and the third tips in... 

The above investigations on charged heterocalixarenes were conveniently extended to hexameric and octameric systems with enlarged cavities, employing (5 +1) and... 

The urea unit in the cyclic urea component of these heterocalixarenes is capped with -(CH2)2-, -(CH2)3- and -CH2-N(Bu )-CH2- moieties. In a straightforward synthetic approach, the bisanions of cyclic ureas, tetrahydropyrimidin-2-one (88JCS(P1)13), 5-t-butyltetrahydro-l,3,5-triazin-2-one (92TL1021, 95JOC6946) and imidazolidin-2-one (92TL1021) on reaction with 1,3-Z)A(bromomethyl)benzene... 

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