Abstract: The invention relates to a process for preparing immediate precursors for pyroxasulfone and fenoxasulfone preparation of the formula (I). The process comprises a bromination of a benzylic position without light irradiation, followed by thoination, which substitutes the bromine atom and after the protecting group is removed, and the revealed thiol or thiolate reacts with a substituted isoxazoline bearing a leaving group at the 3-position. Alternately, the pyroxasulfone or fenoxasulfone immediate precursor is synthesized from arylmethyl bromide by forming a carbon-sulfur bond at the 3-position of a 2-isoxazoline through displacement of a leaving group at the 3-position by an appropriate thionating reagent. The resulting adducts, which is a S-protected 3-thio-2-isoxazoline, may be treated with base to remove the protecting group, to reveal a thiol or thiolate which may subsequently react with the arylmethyl bromide to form the Pyroxasulfone or Fenoxasulfone immediate precursor.