Aromatic nucleophilic substitution. Part 2. Preparation of novel 3‐substituted xanthone and thioxanthone derivatives

The novel 3‐nitro‐9‐oxo‐9H‐xanthene‐ and 3‐nitro‐9‐oxo‐9H‐thioxanthene‐l‐carboxylic acids 2a–d were prepared by intramolecular acylation of 3‐aryloxy‐ and 3‐arylthio‐5‐nitrophthalic anhydrides 1 (Scheme). The 3‐nitro group was readily substituted by O‐ and S‐nucleophiles and halide and azide ions to give a range of 3‐substituted thioxanthone derivatives 3 with varied λmax.