Syntheses and conformational structures of functionalized tetraoxacalix[2]arene[2]triazines

The syntheses and conformational structures of various functionalized tetraoxacalix[2]arene[2]triazines were studied. Applying the fragment coupling approach and the post-macrocyclization chemical manipulations, a number of tetraoxacalix[2]arene[2]triazines that contain, on the lower rim, one or two aldehyde, ester, carboxylic acid, hydroxymethyl, and aminomethyl functional groups were prepared in moderate to high chemical yields from cheap and commercially available materials. On the basis of X-ray crystallography and NMR spectroscopy, all tetraoxacalix[2]arene[2]triazines containing electron-withdrawing group(s) adopted 1,3-alternate conformation both in solution and in the solid state, while tetraoxacalix[2]arene[2]triazines bearing hydroxymethyl and aminomethyl substituent(s) existed as pinched or distorted partial cone conformers due to the formation of intramolecular hydrogen bond between hydroxyl or amino group and triazine ring.