A pyrimidone derivative of general formula I: ** ** Formula as racemate, diastereomeric mixture or enantiomer, wherein: Ar represents phenyl or phenyl substituted with one or more halogen and / or trifluoromethyl R1 is C1-C4 alkyl R2 is hydrogen or C1-C4 alkyl or R1 together with R2 form a polymethylene chain C2-C4 alkyl R3 represents hydrogen, C1-C4 alkyl, C1-C4 haloalkyl or cyclopropyl A represents a benzene ring or ocíclico heter 5- or 6 members in which one or more of the ring atoms is selected from the group consisting of N, O and S and may be optionally fused said rings with a benzene ring or a heterocyclic ring of 5 or 6 members containing one or more heteroatoms selected from N, O and S, and wherein a can be unsubstituted or have 1, 2, 3 or 4 groups W in any of the rings group W represents C1-C4 alkyl, C3-C6, haloalkyl C1-C4, alkoxy C1-C4 alkyl, haloalkoxy C1-C4, halogen, nitro, cyano, hydroxy, benzyloxy, hydroxymethyl, one -NR4R5 group, a -CONR4R5 group , a group -CH 2 OCO-R4, -CO-R4 group, a -COO-R4 group, -SO2R6 group, a -C (> = NR4) NHR7, a group -C (> = NR7) OR4 and additionally one of the groups W can also represent 1-pyrrolyl, 1-imidazolyl, 1H-1,2,4-triazol-1-yl, 5-tetrazolyl (optionally substituted with C1-C4), 1-pyrrolidinyl, 4 alkylmorpholinyl, N-oxide 4-morpholinyl, -X-R8 group one or a group of formulas (i) - (iv): Formula ** ** in which: R4 represents hydrogen, C1-C4 alkyl, C3 C6 alkyl or arylC 1-4 alkyl wherein aryl represents phenyl or phenyl substituted with one or more alkyl groups C1-C4, halogen, C1-C4 haloalkyl, C1-C4 alkoxy or C1-C4 haloalkoxy R5 represents hydrogen, C1-C4 alkyl, C3-C6 a -COR 4 group or a group-COCF3 R6 represents C1-C4 alkyl n represents 0, 1 or 2 R7 represents hydrogen, -CONH2, -COMe, -CN, -SO2NHR4, -SO2R4, -OR4, -OCOR4 or - (C1-4 alkyl) -NH2 X represents a single bond, -O-, -SOz, -NR4- or -C (> = O) - R9 represents C1-C4 alkyl, C3-C6, haloalkyl C1-C4, alkoxy C1-C4 alkyl, haloalkoxy C1-C4, halogen, nitro, cyano a -NR4R5
