A Sonogashira coupling of meta-iodocalix[4]arene with various terminal acetylenes confirmed that the meta position of calixarene is well addressable, and that both thermal and microwave protocols led to good yields of alkynylcalixarenes. Alkynes thus obtained were subjected to the ferric chloride and diphenyl diselenide-promoted electrophilic closure. It turns out that the calix[4]arenes give completely different bridging products than those described for the non-macrocyclic starting compounds. This can be demonstrated not only by the isolation of products with a six-membered ring (6-exo-dig), but mainly by the smooth formation of the 5-endo-dig cyclization, which has never been observed in the aliphatic series. An attempt at electrocyclization led to a high yield of the 1,2-diketone (oxidation of the starting alkyne), again in contrast to the reaction described for the acyclic derivatives. The structures of the unexpected products were unequivocally established by X-ray analysis and clearly demonstrate how the preorganized macrocyclic skeleton favors a completely different regioselectivity of cyclization reactions compared to common aliphatic compounds.

• Keywords
• 6-exo-dig and 5-endo-dig cyclization, Sonogashira coupling, X-ray analysis, alkyne cyclization, calixarene, diphenyl diselenide, electrochemistry, meta-substitution, regioselectivity,
• Publication type
• Journal Article MeSH

The formation of inherently chiral calix[4]arenes by the intramolecular cyclization approach suffers from a limited number of suitable substrates for these reactions. Here, we report an easy way to prepare one class of such compounds: calixquinolines, which can be obtained by the reaction of aldehydes with easily accessible aminocalix[4]arenes in acidic conditions (Doebner-Miller reaction). The synthetic procedure represents a very straightforward approach to the inherently chiral macrocyclic systems. The complexation studies revealed the ability of these compounds to complex quaternary ammonium salts with different stoichiometries depending on the guest molecules. At the same time, the ability of enantioselective complexation of chiral N-methylammonium salts was demonstrated.

• Keywords
• calixarene, chiral recognition, complexation, inherent chirality, mercuration, meta-substitution, quinoline formation,
• MeSH
• Aldehydes * MeSH
• Quinolines * MeSH
• Cyclization MeSH
• Quaternary Ammonium Compounds chemistry   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Aldehydes * MeSH
• Quinolines * MeSH
• Quaternary Ammonium Compounds MeSH