160. Convergent Synthesis, Resolution, and Chiroptical Properties of Dimethoxychromenoacridinium Ions
     Jérôme Gouin, Thomas Bürgi, Laure Guénée, Jérôme Lacour
     Org. Lett. 2014, 16, 3800-3803

Cationic azaoxa[4]helicenes can be prepared in a single step from a common xanthenium precursor by addition of nucleophilic amines under monitored conditions (160 °C, 2 min, MW). The (−)-(M) and (+)-(P) enantiomers can be separated by chiral stationary-phase chromatography. Determination of the absolute configuration and racemization barrier (ΔG^‡ (433 K) 33.3 ± 1.3 kcal·mol^–1) was achieved by VCD and ECD spectroscopy, respectively.

DOI : 10.1021/ol501692r 

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