Preparation of halo-N-aryl-pyrido:pyridone carboxylic acid compounds

Preparation of an N-aryl pyridopyridone carboxylic acid compound (I) of formula (Ia) or (Ib) comprises (a) reacting a halogenated acid chloride (II) of formula (IIa) or (IIb) with an aminoacrylic acid ester of formula (III) to give an intermediate (IV) of formula (A; R3 = R1; R" = R2) or (B; R3 = R1; R" = R2); (b) reacting (IV) with an optionally substituted aniline of formula H2N-Ar (V) to give an intermediate (VI) of formula (A or B; R3 = H; R" = Ar); and cyclising (VI) in the presence of an acid acceptor and optionally saponifying. One of V, W = N and the other = CH; R = H or 1-4C alkyl; Ar = optionally substituted phenyl; X = F, Cl or Br; n = 1 - 3; Y = F or Cl; R' = 1-4C alkyl; R1, R2 = 1-6C alkyl (optionally interrupted by O, S or NH). Compounds (VI) are new.