Abstract
A novel intramolecular oxidative cyclization of the 3,4-diaminophenyl thiourea ( 3) to the 5,6-diaminobenzthiazole ( 4) is reported. This conversion can be brought about by Pd/C in presence of atmospheric oxygen in acid solution. It is likely that the quinone-imine ( 5) is an intermediate in this transformation. Surprisingly catalytic reduction (Pd/C, H 2) of the 4-amino-3-nitrophenyl thiourea ( 2) gave both 3 and 4. A rational ‘one-pot’ reduction-oxidation sequence (iron/acid, ferric chloride) is described for the preparation of this and other such 5,6-diaminobenzthiazoles from the corresponding 4-amino-3-nitrophenyl thioureas.
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