An alternative method for the preparation of the precursor 3-bromo-5-ethylbenzophenone (VI) has been reported. Diazotization of diethyl 5-aminoisophthalate (I), followed by treatment with HBr/CuBr furnishes the bromo isophthalate (II). Partial hydrolysis of diester (II) by means of KOH provides mono-acid (VIII), which is further converted to acid chloride (IX) with PCl5. Subsequent Friedel-Crafts condensation of (IX) with benzene in the presence of AlCl3 leads to benzophenone (X). After protection of ketone (X) as the ethylene ketal (XI), addition of methylmagnesium chloride to (XI) affords the acetyl compound (XII). This is subsequently reduced to the corresponding ethyl derivative (XIII) under Wolff-Kishner conditions. The key benzophenone precursor (VI) is then obtained by acidic hydrolysis of ketal (XIII).

Dimethyl 5-aminoisophthalate (I) is converted into the corresponding 5-bromo derivative (II) via diazotization, followed by Sandmeyer reaction with HBr/CuBr. Addition of methylmagnesium chloride to one of the carboxylate groups of diester (II) leads to methyl 3-acetyl-5-bromobenzoate (III). Ketone (III) reduction with concomitant ester hydrolysis under Wolff-Kishner conditions produces 3-bromo-5-ethylbenzoic acid (IV), which is further chlorinated to (V) by using PCl5 in CCl4. Friedel-Crafts condensation of acid chloride (V) with benzene gives rise to the benzophenone (VI). Finally, palladium-catalyzed coupling of aryl bromide (VI) with vinylsulfonamide (VII) yields the title compound.