Syntheses and crystal structures of a nitro-anthracene-isoxazole and its oxidation product

The syntheses and structures of an unexpected by-product from an iodination reaction, namely, ethyl 5-methyl-3-(10-nitro-anthracen-9-yl)isoxazole-4-carb-oxy-l-ate, C₂₁H₁₆N₂O₅, (I), and its oxidation product, ethyl 3-(9-hy-droxy-10-oxo-9,10-di-hydro-anthracen-9-yl)-5-methyl-isoxazole-4-carboxyl-ate, C₂₁H₁₇NO₅ (V) are described. Compound (I) crystallizes with two mol-ecules in the asymmetric unit in which the dihedral angles between the anthracene fused-ring systems and isoxazole ring mean planes are 88.67 (16) and 85.64 (16)°; both mol-ecules feature a disordered nitro group. In (V), which crystallizes with one mol-ecule in the asymmetric unit, the equivalent dihedral angle between the almost planar anthrone ring system (r.m.s. deviation = 0.029 Å) and the pendant isoxazole ring is 89.65 (5)°. In the crystal of (I), the mol-ecules are linked by weak C-H⋯O inter-actions into a three-dimensional network and in the extended structure of (V), inversion dimers linked by pairwise O-H⋯O hydrogen bonds generate R ₂ ²(14) loops.