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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. |