Synthesis, resolution and crystal structures of two enanti-omeric rhodamine derivatives

The title mol-ecule, rac-6'-bromo-3'-di-ethyl-amino-3H-spiro-[2-benzo-furan-1,9'-xanthen]-3-one, C₂₄H₂₀BrNO₃, was synthesized and the two enanti-omers which formed were separated. The structures of all three compounds were determined and compared with those of a variety of related derivatives. A notable feature is the fold of the xanthene portion which ranges from 15.15 (13)° in the racemate to 2.42 (2)° in one mol-ecule of the R enanti-omer with that for the S enanti-omer having an inter-mediate value. The differences are attributed to the number and severity of inter-molecular inter-actions which include C-H⋯O hydrogen bonds, C-H⋯π(ring) and, in the S enanti-omer, a π-stacking inter-action between the carbonyl group and an aromatic ring.