Structural investigations of 5-hydroxy-4,5-dihydroisoxazoles

The X-ray diffraction data determined for eight 3-(R3), 4-(R4), 4,4-(R4/R4′) and/or 5-(R5) 5-hydroxy-4,5-dihydroisoxazoles [where R3 = Ph, R4/R4′ = H/H, R5 = CCl3 (1); R3 = 4-Br-C6H4, R4/R4′ = H/H, R5 = CCl3 (2); R3 = thien-2-yl, R4/R4’ = H/H, R5 = CCl3 (3); R3 = Ph, R4 = Ph, R4’ = OH, R5 = Me (4); R3 = Me, R4/R4′ = N–OH, R5 = Me (5); R3 = CF3, R4/R4’ = H/H, R5 = CMe2CH2OH (6); R3 = H, R4 = 4-I-C6H4, R4’ = H, R5 = 4-I-C6H4 (7); R3/R4 = –(CH2)3–, R4′ = H, R5 = CF2CF2H (8);] are discussed. The crystalline structure of compounds 1–3 is described for the first time and crystalline structure of compounds 4–8 has already been described in literature. It was found that the supramolecular auto-organization of 1–8 is characterized by hydrogen bonds invariably involving the hemiacetal hydroxyl group. Compound 5 is the only exception, where the hydroxyl oxime group is the participant in the hydrogen bond. Compounds 4 and 8 present intermolecular contact between the hydroxyl group of the hemiacetal and the nitrogen atom of the 4,5-dihydroisoxazole ring. Compound 7 presents similar interaction, where the hydroxyl contact is with the oxygen atom of the 4,5-dihydroisoxazole ring. Moreover, the crystal structure of compound 6 was stabilized by O–H⋯O interaction between the hydroxyl group of hemiacetal and the hydroxyl group of the alcohol function attached at the 5-position of 4,5-dihydroisoxazole. The crystal structure of compounds 1–3, as described here for the first time, was similar to that of compounds 4 and 7, showing a hydrogen bond O(51)-H(51)⋯N(2) between the hydroxyl group and the nitrogen atom of the isoxazoline ring. This means that the crystal structure of these compounds was governed by hydrogen bonds O–H⋯N, involving the hydroxyl of the hemiacetal group and the nitrogen atom of the 4,5-dihydroisoxazole ring. This interaction is relatively robust, showing a pattern in the crystal packing. Compounds 1–3 also have their crystal stabilized by more weak interactions of type Cl⋯Cl, involving the chlorine atom of the trichloromethyl group.