Abstract: The invention relates to a process for preparing a key intermediate of Formula (I) in the synthesis of pyroxasulfone. The process comprises reacting an isoxazole of Formula (II) with a thionating reagent to create an S-substituted thioisoxazole of Formula (III); and combining the S-substituted thioisoxazole of Formula (III) with a pyrazole of the Formula (IV) by introducing a methylene bridge, to obtain a compound of Formula (I). The invention also relates to novel S-substituted thioisoxazole of Formula (III) and processes of preparation thereof, wherein L1 is halogen or an anionic residue derived from an acid; R is an organic residue derived from a suitable thionating reagent: dimethyl thioformamide, thiosulfate salts, dithiooxamide, alkyl xanthate salts, thiobenzamide, V-substituted thiourea and thioacetate salts.

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.

Abstract: The invention provides a process which comprises the step of thiomethylating a pyrazole, to create R2—C(O)—S—CH2— functionality at position 4 of the pyrazole ring. The process is useful in preparing Pyroxasulfone. The invention also provides intermediates.