Convergent Synthesis, Resolution, and Chiroptical Properties of Dimethoxychromenoacridinium Ions
摘要:
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 degrees 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 (Delta G(double dagger) (433 K) 33.3 +/- 1.3 kcal.mol(-1)) was achieved by VCD and ECD spectroscopy, respectively.