A convenient approach to 16-, 19-, and 22-membered 2,2′-Bipyridine thiacrown ethers and their conformation preferences

摘要

A convenient, three-step synthesis of 1:1 thiacrown ether macrocycles 5a-c containing a fused cyclopenteno[c]2,2′-bipyridine subunit: has been accomplished through first homocoupling of 1,2,4-triazine bisulfides 3a-c tethered to polyethylene glycol) chains with potassium cyanide and second Diels-Alder/retro-Diels-Alder reaction of such obtained thiamacrocycles 4a-c with 1-pyrrolidino-1-cyclopentene. Macrocycles 5a-c were oxidized to nonracemic monosulfoxides 6ac by using Davis' oxaziridine and tested in the asymmetric addition of the diethylzinc to benzaldehyde, The crystal structure determinations of 5a-c and. 6b and theoretical calculations at the DFT/B3LYP/6-311G** level were used to establish their cis or irons conformations in the solid state and the gas phase.