Department of Chemistry, Graduate School of Science, Hiroshima University , 1-3-1 Kagamiyama, Higashi-Hiroshima 739-8526, Japan.
J Org Chem. 2017 Dec 15;82(24):13220-13230. doi: 10.1021/acs.joc.7b02301. Epub 2017 Nov 30.
Bisresorcinarenes 1a-d were obtained in excellent yields, and 1e was finally obtained in 50% yield. X-ray diffraction analysis showed that 1a and 1b adopted helical conformations, whereas the two resorcinarenes of 1c-e were in parallel orientations in which the clefts of the aliphatic chains entrapped one or two solvent molecules. The conformational study revealed that the helix interconversion between the (P)- and (M)-helical conformers depended on the length of the aliphatic chains. 1a had the largest energetic barrier to helix interconversion, while in 1b, its more flexible aliphatic chains lowered its energetic barriers. The P/M interconversion of 1a was coupled with the clockwise/anticlockwise interconversion of the interannular hydrogen bonding of the two resorcinarenes. The large negative entropic contributions indicate that the transition state is most likely more ordered than the ground states, suggesting that the transition state is most likely symmetric and is solvated by water molecules. Calculations at the M06-2X/6-31G(d,p) level revealed that the more stable (P)-conformation has clockwise interannular hydrogen bonding between the two resorcinarenes.
双[间苯二酚]轮烷 1a-d 以优异的产率得到，最终以 50%的产率得到 1e。X 射线衍射分析表明，1a 和 1b 采用螺旋构象，而 1c-e 的两个间苯二酚轮烷则呈平行取向，其中脂肪链的裂缝夹带一个或两个溶剂分子。构象研究表明，（P）-和（M）-螺旋构象之间的螺旋互变取决于脂肪链的长度。1a 具有最大的螺旋互变能垒，而在 1b 中，其更灵活的脂肪链降低了其能垒。1a 的 P/M 互变与两个间苯二酚轮烷中环间氢键的顺时针/逆时针互变偶联。大的负熵贡献表明过渡态比基态更有序，这表明过渡态很可能是对称的，并被水分子溶剂化。在 M06-2X/6-31G(d,p)水平上的计算表明，更稳定的（P）构象在两个间苯二酚轮烷之间具有顺时针的环间氢键。
