Stereochemical significance of O to N atom interchanges within cationic helicenes: experimental and computational evidence of near racemization to remarkable enantiospecificity
作者:Geraldine M. Labrador、Céline Besnard、Thomas Bürgi、Amalia I. Poblador-Bahamonde、Johann Bosson、Jérôme Lacour
DOI:10.1039/c9sc02127b
日期:——
Oxygen atoms of cationic dioxa and azaoxa [6]helicenes can be exchanged by amino groups to form azaoxa and diaza [6]helicenes respectively. The mild reaction conditions developed herein allow the construction of libraries of derivatives with sensitive and/or functionalized side chains. Using enantioenriched dioxa or azaoxa helicene precursors, these exchanges lead to either near racemization (es 3%)
A series of water-soluble helicene dyes generating intense electrochemiluminescence (ECL) signal in physiological conditions is reported. Those species were prepared using diaza [4] and [6]helicenes as structural cores modified with sulfonate groups in various positions. Such groups improve their water solubility and can induce a red-shifted emission. Efficient ECL up to the near-infrared is achieved
[6]-appeal: Direct late-stage functionalization at the terminalends of cationic diaza helicenes is readily achieved under thermodynamic control, in polyphosphoric acid or Eaton′s reagent as solvent. This orthogonal regioselectivity can be used to generate extended [5] or [6]helicenes in successive one-pot elongation processes. Retention of configuration and excellent enantiospecificity (up to 99 %) are furthermore
A series of helical tetracenes and pentacenes was synthesized from cationic [6] and [4]heliceneprecursors. These colorful acenes fluoresce in the far red region. While [4]helicene-based pentacenes exhibit chiropticalproperties mainly in the UV region, [6]helicene-derived tetracenes show enhanced ECD in the visible range, in addition to clear CPL responses. This difference is rationalized using first