In the title compound, C15H13NO2S, the benzothia­zole unit is essentially planar [maximum deviation = −0.0099 (5) Å for the S atom] and is oriented at a dihedral angle of 4.8 (5)° with respect to the benzene ring. An intra­molecular O—H⋯N hydrogen bond generates an S(6) ring motif. The crystal packing is stabilized by C—H⋯π inter­actions.

Copper­(II) catalyzed and uncatalyzed oxidation of ornithine by peroxomonosulfate (PMS) was studied in acetic acid–sodium acetate buffered medium (pH 3.6–5.2). The catalyzed reaction was 2.6 times faster than the uncatalyzed reaction. The catalytic constant k c obtained in this study was 0.15 mol–1 dm3 s–1. A negative value of entropy of activation obtained in this reaction revealed that the transition state was more rigid than the reactants. ESR spectral data ruled out the participation of free radical intermediate. Cyclic voltammetric and absorption studies confirmed the formation of copper–ornithine–PMS complex. HPLC analysis revealed that the product formed in this reaction was 4-aminobutanal, which was confirmed by NMR spectra.

This comprehensive study portrays that p-toluenesulfonic acid is a more efficient catalyst for the reaction between p-quinones and 3,4-dihydro-2H-pyran, than the Lewis acids. The products were accomplished by the Diels-Alder cycloaddition reaction and their mechanistic pathways have been formulated. The impact of C and C substituents of the p-quinones on the cycloaddition reaction has been explored. Remarkably, it is the first report to explore this kind of in situ generated diene for the Diels-Alder cycloaddition reaction.

The complete molecule of the title compound, C 16 H 22 O 4 , is generated by crystallographic inversion symmetry. The oxane ring system adopts a chair conformation with the exocyclic C-C bond in an axial orientation; the dihedral angle between the oxane ring (all non-H atoms) and the benzene ring is 73.45 (1) . A short intramolecular C-HÁ Á ÁO contact occcurs. In the crystal, a very weak C-HÁ Á Á interaction generates [010] chains. Structure descriptionThe 4H-pyran nucleus occurs in molecules possessing a wide spectrum of biological and pharmacological activities (Shehab & Ghoneim, 2016). As part of our studies in this area, we have undertaken the X-ray crystal structure analysis of the title compound (Fig. 1).The title compound contains a half of the molecule in an asymmetric unit; the complete molecule is generated by crystallographic inversion symmetry with the inversion point at (1, 0, 1) for the asymmetric molecule. The oxane ring (C1-C5/O1) adopts a chair conformation: the mean plane of the oxane ring makes a dihedral angle of 73.45 (1) with the benzene ring. A short intramolecular C-HÁ Á ÁO contact occurs. In the crystal, a very weak C-HÁ Á Á interaction (Table 1) generates [010] chains (Fig. 2). Synthesis and crystallizationA solution of p-quinone (2.0 mmol), 3,4-dihydro-2H-pyran (5.0 mmol) and pTsOH (1.0 mmol) in 1,2-dichloroethane (5 ml) was stirred at 83 C under an oxygen atmosphere. The progress of the reaction was monitored by TLC (20% ethyl acetate/hexane). After completion, it was concentrated and the residue was subjected for separation of the