The synthetic sequence to make 4-[4′-bis (2 ″-chloroethyl) aminophenyl]-4, 4- difluorobutanoic acid {4, 4-difluorochlorambucil} was not taken beyond the intermediate stage involving methyl 4, 4-difluoro-4-(4′-aminophenyl) butanoate, since this amine was hydrolytically unstable. Reaction of methyl 4-(3′-nitrophenyl)-4-oxobutanoate with sulfur tetrafluoride, followed by hydrogénation, afforded the stable isomer, methyl 4, 4-difluoro-4- ...
