. . . . . "A process for producing a compound of general formula (II) wherein each of X1 and X2 is a hydrogen atom, a halogen atom, an amino group, a mono(lower alkyl)amino group, a di(lower alkyl)amino group, a hydroxyl group, a lower alkoxy group, an aralkoxy group, a carboxyl group, a lower alkoxycarbonyl group, a lower alkanoyloxy group or a lower alkyl group; and R is a hydrogen atom, an amino group, a" .