A convenient method has been developed for the synthesis of a focused library of eight 3-arylimidazo[2,1-b][1,3]thiazoles 4a–h, seven of which have been obtained for the first time. The approach is based on the cyclization of 2-(aroylmethylthio)imidazoles 3a–h under the action of polyphosphoric acid. The structure of the intermediate derivatives of thioimidazoles 3a-h and the imidazothiazoles 4a-h thus obtained was characterized using ¹H, ¹³C NMR spectra and LC-MS. Testing all obtained compounds for antioxidant activity showed that 2-[(1H-imidazol-2-yl)thio]-1-arylethanones 3a–h exhibit a higher ability to inhibit DPPH radicals compared to their cyclic analogues, 3-arylimidazo[2,1-b]thiazoles 4a–h. The highest antioxidant activity was demonstrated by compound 3b (I = 96.3%), which also showed high binding affinity to the Kelch domain of the Keap1 protein in docking studies.