Convergent Synthesis, Resolution, and Chiroptical Properties of Dimethoxychromenoacridinium Ions

Abstract

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 (−)-(<i>M</i>) and (+)-(<i>P</i>) enantiomers can be separated by chiral stationary-phase chromatography. Determination of the absolute configuration and racemization barrier (Δ<i>G</i>^⧧ (433 K) 33.3 ± 1.3 kcal·mol^–1) was achieved by VCD and ECD spectroscopy, respectively