Thiophene-Based Double Helices: Syntheses, X-ray Structures, and Chiroptical Properties

Sheng Zhang, Xinming Liu, Chunli Li, Lu Li, Jinsheng Song, Jianwu Shi, Martha Morton, Suchada Rajca, Andrzej Rajca, Hua Wang

Research output: Contribution to journalArticle

18 Scopus citations

Abstract

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.

Original languageEnglish (US)
Pages (from-to)10002-10010
Number of pages9
JournalJournal of the American Chemical Society
Volume138
Issue number31
DOIs
StatePublished - Aug 10 2016

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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