The chlorination of 6-choro-1,4-naphthoquinone (I) with Cl2 in acetic acid gives 2,3,6-trichloro-2,3-dihydro-1,4-naphthoquinone (II), which is treated with sodium acetate and Cl2 in refluxing acetic acid yielding 2,3,6-trichloro-1,4-naphthoquinone (II) The reaction of (III) with sodium methoxide in reftuxing methanol affords 6-chloro-2,3-dimethoxy-1-4-naphthoquinone (IV), which is finally reduced with H2 over Pd/C IP THF, and acetylated with acetic anhydride in pyridine (I).

The chlorination of 6-choro-1,4-naphthoquinone (I) with Cl2 in acetic acid gives 2,3,6-trichloro-2,3-dihydro-1,4-naphthoquinone (II), which is treated with sodium acetate and Cl2 in refluxing acetic acid yielding 2,3,6-trichloro-1,4-naphthoquinone (II) The reaction of (III) with sodium methoxide in reftuxing methanol affords 6-chloro-2,3-dimethoxy-1-4-naphthoquinone (IV), which is finally reduced with H2 over Pd/C IP THF, and acetylated with acetic anhydride in pyridine (I).

The metalation of 4-chlorobromobenzene (I) with lithium gives 4-chlorophenyllithium (II), which is condensed with dimethyl squarate (III) in THF at -78 C giving 4-(4-chlorophenyl)-4-hydroxy-2,3-dimethoxy-2-cyclobuten-1-one (IV). The isomerization of (IV) in refluxing xylene (38 C) affords naphthohydroquinone (VI) through the intermediate ketene (V). Finally, compound (VI) is acetylated with acetic anhydride in pyridine - dimethylaminopyridine.