| abstract |
Compounds of formula I, V, VI and II, and processes for their preparation, wherein R1, R2 and R3 are the same or different and signify hydrogens, halogens, alkyl, alkyloxy, hydroxy, nitro, alkylcarbonylamino, alkylamino or dialkylamino group; and R4 is alkyl or aryl. There is also provided a process for preparing a compound of formula B from the compounds of formula V and I. |