Synthesis and biological activities of substituted 4,4,4-trifluoro-3-(indole-3-)butyric acids, novel fluorinated plant growth regulators

Substituted 4,4,4-trifluoro-3-(indole-3-)butyric acids (TFIBAs), novel fluorinated plant growth regulators, were easily synthesized from substituted 2,2,2-trifluoro-1-(indole-3-)ethanols. The synthetic substituted TFIBAs showed marked root growth-promoting activity toward Chinese cabbage, lettuce, and rice plants. 5-MeO-2-Me-TFIBA (2d) had especially strong promoting activity toward Chinese cabbage, while 5-Me-TFIBA (2b) markedly promoted the root growth of all three plants, The promoting activity of TFIBAs halogenated at the 5-position in the indole nucleus of the molecule (5-Br- and 5-Cl-TFIBA (2e and 2g)) was also greater than the activity of TFIBA, the original non-substituted compound. 5-NO2-TFIBA (2h) with a strong electron-withdraw-in group showed only very weak root growth-promoting activity.