The reaction of 4-bromoaniline (I) with potassium thiocyanate and bromine in acetic acid gives the benzothiazole (III) through the intermediate (II). The hydrolysis of (III) with NaOH affords 4-bromo-2-sulfanylaniline (IV), which is cyclized with 4-hydroxy-6-methyl-2-oxo-3-cyclohexene-1-carboxylic acid tert-butyl ester (V) in refluxing toluene.