Cyclization of 1-arylthiosemicarbazides to benzothiazoles

It is known that 1-arylthiosemicarbazides are cyclized to 2-aminobenzothiazoles in acidic media. This reaction was extended to 1,3- and 1,4-disubstituted thiosemicarbazides. It is shown that the rearrangement proceeds through a step involving the formation of o-aminophenylisothioureas. The reaction conditions and substituents in the benzene ring or attached to the nitrogen atoms of the thiosemicarbazides do not have a substantial effect on the ratio of the resulting 2-amino- and 2-phenyl(methyl)aminobenzothiazoles (11). In the case of m-chlorophenylthiosemicarbazide, 5- and 7-chloro-2-aminobenzothiazoles are obtained in equimolar amounts, whereas the 7 isomer (52) is the major product from m-tolylthiosemicarbazide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 467–475, April, 1978.