β-Enaminones and organic salts from 3-benzoyl-4‑hydroxy-6-phenyl-2H-pyran-2-one: Synthesis, X-ray crystal structural studies and antimicrobial activity

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The reactivity of pyran-2,4‑dione 1 towards primary amines (propylamine and p-toluidine) and secodary amines (morpholine and piperidine) were investigated. The reactions were proceeded by replacement of the external alcoholic hydroxyl group with primary amine accompanied by loss of water molecule to give β-enamino-pyran-2,4-diones 2 and 3. In case of secondary amines, a transfer of the phenolic proton of pyrone ring to the secondary amine nitrogen leading to the formation of the corresponding quaternary ammonium salts of morpholine 4 and piperidine 5, respectively. The X-ray single crystal structures of 2 and 4 proved with no doubt the proposed structure based on the spectral characterization. The percentages of the H…H, O…H, and C…H interactions are in the range of 49.2–50.6 %, 19.6–19.8 and 27.6–28.6 %, respectively in case of 2 based on Hirshfeld topology analysis. For the two cationic units in 4, the C…H (15.9–18.5 %), H…H (42.9–43.1) and O…H (38.2–40.5 %) are the most important. The two anionic units showed different types of intermolecular interactions. In one unit, the O…H (23.4 %), C…H (28.4 %) and C…C (1.3 %) contacts are the most important while in the other anionic unit the O…H (23.3 %), C…H (26.7 %), C…O (5.7 %) and C…C (1.6 %) interactions are the most significant. The inhibition zones of 1 (18 mm), 4 (22 mm), and 5 (20 mm) indicated greater activity against S. aureus, compared to streptomycin (16 mm) and neomycin (13 mm). Compounds 1–5 showed nearly two-fold as much antifungicidal activity against C. albicans compared to some conventional medicines such as Neomycin and Streptomycin.