Compounds of formula (I):wherein:R1and R2, which may be the same or different, each represent a hydrogen or halogen atom or an alkyl, alkoxy, alkylthio, acyl, alkoxycarbonyl, carboxy, hydroxy, hydroxyalkyl, cyano, nitro, amino, substituted or unsubstituted aminocarbonyl, aminosulphonyl, alkylsulphonylaminoalkyl, N-hydroxycarboximidamide or benzyloxy group,R3represents a hydrogen atom or an alkyl, cycloalkyl or cycloalkylalkyl group,R4represents a hydrogen atom or a substituted or unsubstituted alkyl group本發明係關於一種式(I)化合物:其中:R1及R2可係相同或不同,且各表示氫或鹵原子或烷基、烷氧基、烷硫基、醯基、烷氧羰基、羧基、羥基、羥烷基、氰基、硝基、胺基,經取代或未經取代之胺基羰基、胺磺醯基、烷磺醯胺基烷基、N-羥基-甲醯亞胺醯胺基或芐氧基,R3表示氫原子或烷基、環烷基或環烷基烷基,R4表示氫原子或經取代或未經取代之烷基。