A facile approach to 2,2'-bipyridine based thiacrown ethers and their sulfoxides by DA-rDA reaction of 5,5'-bi-1,2,4-triazine thiamacrocycles. The conformation studies

Diels-Alder/retro Diels-Alder (DA-rDA) reactions of 5,5′-bi-1,2,4-triazine thiamacrocycles 4a–c afforded medium-size 2,2′-bipyridine based thiacrown ethers 5a–c in good yield. The latter were oxidized to non-racemic monosulfoxides 7a–c using Davis oxaziridine and tested as chiral auxilaries in the asymmetric addition of diethyl zinc to benzaldehyde. The theoretical calculations at DFT /B3LYP/6-311G** level were conducted thus establishing cis or trans conformational preferences of the target thiamacrocycles.