A novel approach to conformationally strained 2,2′-bipyridine thiacrown ethers and their chiral sulfoxides by sequential homo-coupling/DA–rDA reaction of 5,5′-bi-1,2,4-triazine-containing thiamacrocycles

The synthesis of conformationally strained 2,2′-bipyridine thiamacrocycles 5, 6, 9, 10 and their chiral sulfoxides 11–14 is elaborated using, (1) homo-coupling of 1,2,4-triazine sulfide 3 with potassium cyanide and (2) Diels–Alder/retro Diels–Alder (DA–rDA) with 2,5-norbornadiene or 1-pyrrolidino-1-cyclopentene as the key steps. The crystal structure determinations of 4–6 and the theoretical calculations at DFT/B3LYP/6-311G∗∗ level were conducted thus establishing conformational preferences of the target thiamacrocycles