Synthesis, DFT Study and Antibacterial Activity of some Isoxazoline Derivatives Containing 1,4-benzothiazin-3-one Nucleus Obtained Using 1,3-dipolar Cycloaddition Reaction

Novel series of isoxazoline derivatives containing 1,4-benzothiazin-3-one ring (6a-h) were synthesized via 1,3-dipolar cycloaddition reactions of arylnitrile oxides 5a-d on 4-allyl-2-(substituted)-1,4-benzothiazin-3-ones 3 and 4 led to polyheterocyclic. Systems. During our work, we mainly focused on the reactivity of nitrile oxides with carbon-carbon extracyclic double bond of the allyl group. The reaction leads exclusively to cycloadducts 6a-h with a good yield. The compounds were characterized using s spectral data (1H-NMR, 13C-NMR) and for some structures were also confirmed via single-crystal X-ray diffraction techniques. Density Functional Theory (DFT) optimized structures at the B3LYP/ 6–311G(d,p) level are compared with the experimentally determined molecular structure in the solid-state. The HOMO—LUMO behavior was elucidated. The results are in agreement with the experimental data. The newly synthesized compounds 1, 2, 3, 4, 6a-g using cycloaddition reactions were evaluated in vitro for their antibacterial activities against some Gram-positive and Gram-negative microbial strains. Several compounds tested showed significant activity.