Microwave-assisted synthesis of s-triazino[2,1-b][1,3]benzoxazoles, s-triazino[2,1-b][1,3]benzothiazoles, and s-triazino[1,2-a]benzimidazoles

2-Amino-4-oxo-derivatives of s-triazino[2,1e][1,3]benzoxazoles, s-triazino[2,1,b][1,3]benzothiazoles, and s-triazino[1,2-a]benzimidazoles were synthesized by carbonylation of 2-benz-oxazolylguanidines, 2- benzothiazolylguanidines, and 2-benzimidazolylguanidines with phenyl isocyanate under microwave irradiation (180°C, 15 minutes). Using phenyl isothiocyanate instead of phenyl isocyanate under the same conditions led to the successful ring closure via thiocarbonylation of 2-benzoxazolylguanidines. However, the formation of 2-imino-4-phenylimino-s-triazino[2,1-b][1,3]benzothiazoles from 2-benzothiazolylguanidines was observed instead under microwave irradiation conditions.