Azacalix[4]arene tetramethyl ether with inherent chirality generated by substitution on the nitrogen bridges

The first inherently chiral azacalix[4]arene has been prepared by introducing three benzyl groups onto the nitrogen bridges. The highly enantioenriched compound was easily obtained via a moderately enantioselective cyclization followed by a simple crystallization procedure. NMR and X-ray crystallographic studies revealed that easy access to the enantiomer was permitted by the non-racemizable 1,3-alternate conformation in solution, up to 110 °C, as well as by the preferential crystallization of a racemic compound.

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2,8,14-Tribenzyl-5,11,17,23-tetra-tert-butyl-25,26,27,28-tetramethoxy-2,8,14,20-tetraazacalix[4]areneC65H78N4O4[α]D27=-122.5 (c 0.1, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: undetermined