Synthesis of 2-Arylbenzothiazoles by DDQ-Promoted Cyclization of Thioformanilides; A Solution-Phase Strategy for Library Synthesis

Several substituted benzothiazoles were synthesized by the intramolecular cyclization of thioformanilides using 2,6-dichloro-3,5-dicyano-1,4-benzoquinone (DDQ) in dichloromethane at ambient temperature in high yields. The resulting 2-arylbenzothi-azoles were separated from the reduced DDQ byproduct 4,5-dichloro-3,6-dihydroxyphthalonitrile by treatment of the reaction mixture with a strongly basic ion-exchange resin. This protocol offers a high degree of flexibility with regard to the functional groups that can be placed on the benzothiazole ring or 2-aryl moiety, which in turn generates scaffolds for parallel synthesis.