The 1,2-alternate conformation, so far the least accessible atropisomer of calixarene, is now easily available on a gram scale. The entire synthetic sequence consists of only two steps—(a) proximal dialkylation (R1-I, NaH/DMF), and (b) another subsequent dialkylation (R2-I, Me3SiOK/THF). The selection of appropriate base/solvent combinations in both stages was the key prerequisite for the successful preparation of the 1,2-alternate conformers, which are available without the use of any protecting groups.
- Conformational mobility
- Partial cone