A facile synthesis of 2-aminothiazolo[5,4-b]pyridines and2-aminobanzoxazoles via cyclization of thioureas

2-Aminothiazolo[5,4-b]pyridines and 2-aminobenzoxazoles havebeen synthesized from 2-hydroxy-3-thioureidopyridine and 2-hydroxy-3-thioureidobenzene respectively via acid catalyzed cyclization, which were prepared by the reaction of isothiocyanates with 2-hydroxy-3-aminopyridine or 2-aminophenol. The hydroxyl group of N-(2-hydroxy-5-phenyl)-N′-phenyl thiourea reacted as nucleophile to thioureido carbon to give 2-aminobenzoxazoles, whereas that of N-(2-hydroxypyridino)-N′-phenylthiourea was reacted as leaving group upon nuclephillic sulfur of thiourea group in the presence of trifluoroacetic acid or phosphoric acid.