The cyclization of 2-amino-6-isoproylphenol (I) with 2-bromo-3-methylbutyryl chloride (II) by means of NaHCO3 in ethyl acetate - water gives 2,8-diisopropyl-2H-1,4-benzoxazin-3(4H)-one (III), which is condensed with methyl bromoacetate (IV) by means of NaH in DMF yielding 2,8-diisopropyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazin-4-acetic acid methyl ester (V). The reaction of (V) with P2S5 in refluxing toluene affords the corresponding thioxo derivative (VI), which is finally hydrolyzed with NaOH in dioxane - methanol.