Abstract The condensation behaviour of various fluorine containing 3-indolylimino derivatives with mercaptoacetic acid and with chloroacetyl chloride has been studied. The cyclocondensation of 3-arylimino-2H-indol-2-ones (III; Ar= 4 FC 6 H 4, 3 CF 3 C 6 H 4, 2 Cl 3 CF 3 C 6 H 3, 2, 3, 4, 5-tetra-FC 6 H and 2, 3, 4, 6-tetra-FC 6 H) with mercaptoacetic acid yielded 3′-phenylspiro [3H-indole-3, 2′-thiazolidine]-2, 4′(1H)-diones (IV) in 75– ...