Synthesis and structures of three isoxazole‐containing Schiff bases

The synthesis and structures of three isoxazole‐containing Schiff bases are reported, namely, (E)‐2‐{(isoxazol‐3‐yl)imino]methyl}phenol, C₁₀H₈N₂O₂, (E)‐2‐{(5‐methylisoxazol‐3‐yl)imino]methyl}phenol, C₁₁H₁₀N₂O₂, and (E)‐2,4‐di‐tert‐butyl‐6‐{(isoxazol‐3‐yl)imino]methyl}phenol, C₁₈H₂₄N₂O₂. All three structures contain an intramolecular O—H…N hydrogen bond, alongside weaker intermolecular C—H…N and C—H…O contacts. The C—O(H) and imine C=N bond lengths were consistent with structures existing in the enol rather than the keto form. Despite having dihedral angles <25°, none of the compounds were observed to be strongly thermochromic, unlike their anil counterparts; however, all three compounds showed a visible colour change upon irradiation with UV light.