Sterically hindered N-aryl-2(1H)-quinolones and N-aryl-6(5H)-phenanthridinones: separation of enantiomers and barriers to racemization

The novel N-aryl-4-chloro-3-methyl-2(1H)-quinolones (1)–(4) have been synthesized by condensation of the appropriate diphenylamine with diethyl methylmalonate and subsequent chlorination of the resulting N-aryl-4-hydroxy-3-methyl-2(1H)-quinolones (7)–(10). 5-(1-Naphthyl)-6(5H)-phenanthridinone (5) has been synthesized by the Chapman rearrangement of the 6-(1 -naphthoxy)phenanthridine (11). Separation of the enantiomers (M) and (P) of the quinolones (1)–(4) and phenanthridinones (5), (6) was achieved by liquid chromatography on triacetylcellulose. The barriers to partial rotation about the C–N bond in (1)–(6) were determined by thermal racemization of enantiomers and are compared with those of structurally related molecules.