The Friedel Krafts reaction of fluorobenzene (I) and 3-nitro-4-chlorobenzoyl chloride (II) by means of AlCl3 gives 3-nitro-4-chloro-4?fluorobenzophenone (III), which by reaction with NH3 in ethylenglycol at 130 C yields 3-nitro-4-amino-4?fluorobenzophenone (IV). The reduction of (IV) with H2 over Pd/C in methanol affords 3,4-diamino-4?fluorobenzophenone (V), which is finally cyclized with S-methylthiourea (VI) and methyl chloroformate by means of NaOH in water