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 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.
thioformanilide - solution phase - cyclization - 2,6-dichloro-3,5-dicyano-1,4-benzoquinone
- benzothiazole - sulfanyl radical
