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Heterocalixarenes. 1. Calix[2]uracil[2]arene:  Synthesis, X-ray Structure, Conformational Analysis, and Binding Character

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posted on 24.09.1999, 00:00 by Subodh Kumar, Geeta Hundal, Dharam Paul, Maninder Singh Hundal, Harjit Singh
1,3-Bis[(1-uracilyl)methyl)]benzene derivatives 3, formed by selective N-1 alkylation of 1,3-bis(trimethylsilyloxy)pyrimidine with 1,3-bis(bromomethyl)benzene derivatives 2, on cyclization with the same or different derivative of 2, provide calix[2]uracil[2]arenes 4. Their conformations, investigated through X-ray, variable temperature 1H NMR, and molecular modeling MM2 calculations, are found to depend on the nature of substituent(s) on the position 2 of 1,3-phenylene rings. 4a exists in equilibrium between various conformations, and 4b, 4d4i adopt an inward flattened partial cone conformation. In 4j, the equilibrium is restricted to two conformations at −60 °C, but the 4j·ethanol complex (2:1), in the solid state, has a cone conformation with ethanol being a H-bond donor through H of OH and CH2 and an acceptor through O of OH. 4d, 4j, and 4k exhibit significant preferences toward alkaline earth metal ions over alkali metal ions though overall bindings are poor.

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