| abstract |
B represents N or X1 and X2 represents O or S(O)n. R, Ra, Rb, Rc, Rd, Re, Rf and Rx represent radicals such as hydrogen, fluorine, chlorine, hydroxyl, (C1-C6)-alkyl, halo-(C1-C6)-alkyl, (C1-C6)-alkyloxy, (C1-C6)-alkylthio and cyano, or Ra and Rb or Rc and Rd or Re and Rf in each case together represent an oxo or a thiooxo group. |