Here derivatives of imidazo[2,1-b][1,3]thiazines are attractive objects for organic and medicinal chemists. In the present work chemoselective conditions for oxidation of the sulfur atom in the 6-(2-pyridinyloxy)substituted (benzo)imidazo[2,1-b][1,3]thiazines to the corresponding sulfoxides were proposed and their synthesis was performed. Synthesized sulfoxides exist in the diastereomeric mixture and individual diastereomers 2a-e and 3a-e were obtained using a chromatographic technique. The structure of compounds 2a-e and 3a-e were characterized using ¹H, ¹³C NMR, LC-MS spectra, and X-ray analysis for derivative 2b. The anti-inflammatory activity screening in vivo was performed using the carrageenan model of inflammatory paw edema in white rats for all the diastereomeric mixtures and individual diastereomers. Diastereomer 2c possessed an anti-inflammatory effect with an inflammation inhibition index of 46.1% which was equal to the activity of the reference drug diclofenac sodium.