Syntheses and conformations of the p-tert-butylcalix[4] arenethiols

The reaction of dimethyl(thiocarbamoyl) chloride with p-tert-butylcalix[4]arene under various conditions yields mixtures from which most of the conformers of the mono-, bis-, tris-, and tetrakis(dimethyl(thiocarbamoyl))oxy compounds have been isolated and purified. Thermal rearrangement of these compounds produces the (dimethylcarbamoyl)thio compounds which, upon reduction with LiAlH4, afford the tetrathiol 14, the trithiol 16, the 1,3-dithiol 21, and the monothiol24. X-ray crystallographic structure determinations and variable-temperature H-1 NMR studies show that the tetrathiol exists as an immobile 1,3-alternate conformer, the trithiol as a semimobile partial cone/1,3-alternate conformer, the 1,3-dithiol as a mobile flattened cone conformer; and the monothiol as a mobile cone conformer. Although the tetrakis(( dimethylcarbamoyl)thio) compound exists in three noninterconverting forms comprising the 1,2-alternate 13, partial cone 18, and 1,3-alternate 19 conformers, all three yield the same tetrathiol 14 upon reduction. Similarly, the syn 22 and anti 20 conformers of the 1,3-bis((dimethylcarbamoyl)thio) compound yield the same dithiol 21. Molecular mechanics calculations for each of the conformers of the mono-, 1,3-di-, tri-, and tetrathiols show general agreement with the X-ray data.