Asymmetric Synthesis of Inherently Chiral Tetraoxacalix[2]arene[2]pyridines via S<inf>N</inf>Ar-Based Cross-Cyclotetramerization

Potassium phosphate-promoted cross-cyclotetramerization of 2,6-dichloro-3-nitropyridine 1 with resorcinol derivatives 2 gave rise to thermodynamically favored 1,3-alternate tetraoxacalix[2]arene[2]pyridines and kinetically controlled 1,2-alternate isomers. The kinetic product could convert into its 1,3-alternate conformational isomer by a macrocycle to macrocycle conversion pathway. Enantiomerically enriched C2-symmetric inherently chiral tetraoxacalix[2]arene[2]pyridines were synthesized via a Cinchonine-derived chiral phase-transfer catalyst (PTC). This synthesis involved the cross-cyclotetramerization of 1 with 2, featuring a key enantioselective intramolecular aromatic nucleophilic substitution (SNAr) step.