[3.3]Dithia-bridged cyclophanes featuring a thienothiophene ring: synthesis, structures and conformational analysis

• Main Authors: Sabir H. Mashraqui, Yogesh Sanghvikar, Shailesh Ghadhigaonkar, Sukeerthi Kumar, Auke Meetsma, Elise Trân Huu Dâu
• Format: Article
• Language: English
• Published: Beilstein-Institut 2009-12-01
• Series: Beilstein Journal of Organic Chemistry
• Subjects: conformational energy minimization; [3.3]dithia-bridged cyclophanes; dynamic NMR analysis; thieno[2,3-b]thiophene; X-ray crystal structure
• Online Access: https://doi.org/10.3762/bjoc.5.74

The synthesis of [3.3]dithia-bridged cyclophanes 7, 9 and 11 incorporating a fused heterocycle, thieno[2,3-b]thiophene is described. The structures are established by 1H NMR analysis and, in the case of 11, also by single crystal X-ray crystallography. Conformational analysis by variable temperature NMR suggests that cyclophanes 7, 9 and 11 exhibit conformationally rigid bridges and rings at least up to 130 °C. Energy minimization of 11 revealed anti-11 to be the most stable conformation. Although, the computed energy difference between the most stable conformation anti-11 and the next higher energy conformation syn-anti-11 is only 2.98 kJ/mol, it is intriguing that 11 does not exhibit thia-bridge inversion even at elevated temperatures.