Asymmetric Synthesis of Inherently Chiral Tetraoxacalix[2]arene[2]pyridines via SNAr-Based Cross-Cyclotetramerization
Regina Ibragimova1, Qiu-Lin Lu1, Mei-Xiang Wang1
1Key Laboratory of Bioorganic Phosphorus Chemistry and Chemical Biology (Ministry of Education), Department of Chemistry, Tsinghua University, Beijing, 100084, China.
Abstract:
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.
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