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-arylbenzothiazoles were separated from the reduced DDQ by product 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.