TY - JOUR
T1 - Thiophene-Based Double Helices
T2 - Syntheses, X-ray Structures, and Chiroptical Properties
AU - Zhang, Sheng
AU - Liu, Xinming
AU - Li, Chunli
AU - Li, Lu
AU - Song, Jinsheng
AU - Shi, Jianwu
AU - Morton, Martha
AU - Rajca, Suchada
AU - Rajca, Andrzej
AU - Wang, Hua
N1 - Funding Information:
We gratefully acknowledge the support of this research by the National Science Foundation (US, CHE-1362454) and the National Natural Science Foundation of China (21270255, 20972041, and 21404031), as well as Innovation Scientists and Technicians Troop Construction Projects of Henan Province (C20150011).
PY - 2016/8/10
Y1 - 2016/8/10
N2 - We demonstrate facile and efficient construction of conjugated double helical ladder oligomers from the saddle-shaped cyclooctatetrathiophene (COTh) building blocks. The key step involves deprotonation of tetra[3,4]thienylene (β,β-COTh) with n-BuLi which displays remarkably high ipsilateral selectivity. Three racemic double helical ladder oligomers, rac-DH-1, rac-DH-2, and rac-DH-3, containing two, three, and five COTh annelated moieties are efficiently synthesized by diastereoselective coupling of the racemic precursors. The X-ray crystallographic studies of rac-DH-1, rac-DH-2 and rac-DH-3 unambiguously revealed that each double helical scaffold has two single helices intertwined with each other via the C-C single bonds. Following removal of TMS groups, double helical ladder oligomer rac-DH-1-D had sufficient solubility to be resolved via chiral HPLC, thus enabling determination of its chirooptical properties such as CD spectra and optical rotation. (+)-DH-1-D has a large barrier for racemization, with lower limit of ΔG‡ > 48 kcal mol-1, which may be compared to DFT-computed barrier of 51 kcal mol-1. The enantiomers of DH-1-D show 1 order of magnitude stronger chirooptical properties than the carbon-sulfur [7]helicene, as determined by the anisotropy factor g = Δϵ/ϵ = -0.039, based on Δϵmax = -11 and ϵ = 2.8 × 102 L mol-1 cm-1 in cyclohexane at 327 nm.
AB - We demonstrate facile and efficient construction of conjugated double helical ladder oligomers from the saddle-shaped cyclooctatetrathiophene (COTh) building blocks. The key step involves deprotonation of tetra[3,4]thienylene (β,β-COTh) with n-BuLi which displays remarkably high ipsilateral selectivity. Three racemic double helical ladder oligomers, rac-DH-1, rac-DH-2, and rac-DH-3, containing two, three, and five COTh annelated moieties are efficiently synthesized by diastereoselective coupling of the racemic precursors. The X-ray crystallographic studies of rac-DH-1, rac-DH-2 and rac-DH-3 unambiguously revealed that each double helical scaffold has two single helices intertwined with each other via the C-C single bonds. Following removal of TMS groups, double helical ladder oligomer rac-DH-1-D had sufficient solubility to be resolved via chiral HPLC, thus enabling determination of its chirooptical properties such as CD spectra and optical rotation. (+)-DH-1-D has a large barrier for racemization, with lower limit of ΔG‡ > 48 kcal mol-1, which may be compared to DFT-computed barrier of 51 kcal mol-1. The enantiomers of DH-1-D show 1 order of magnitude stronger chirooptical properties than the carbon-sulfur [7]helicene, as determined by the anisotropy factor g = Δϵ/ϵ = -0.039, based on Δϵmax = -11 and ϵ = 2.8 × 102 L mol-1 cm-1 in cyclohexane at 327 nm.
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U2 - 10.1021/jacs.6b05709
DO - 10.1021/jacs.6b05709
M3 - Article
C2 - 27440376
AN - SCOPUS:84981555679
SN - 0002-7863
VL - 138
SP - 10002
EP - 10010
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 31
ER -