Pyridines 1-ureido

Bei der thermischen Behandlung cyclokondensieren 2-Oxo-l-ureido-l,2-dihydro-pyridine zu -2-olaten226 ... 

Some ureido- and thioureidopyrazines have been prepared from aminopyrazines with phenyl isocyanate in pyridine, potassium thiocyanate in acid solution, and with phenyl or isopropyl isothiocyanate in pyridine. Thus 2-amino-3-carbamoyl(and jV-benzylcarbamoyl)-5,6-diphenylpyrazines refluxed with phenyl isocyanate in... 

Using hydroxylamine leads to pyridine 1-oxides provided that the 2- and 6-substituents are not too bulky 1119 using semicarbazide leads to 1-ureido-pyridines,1119 and using phenylhydrazine leads to the interesting 1120 l-(aryl-amino)pyridines1120,1121 which cannot be obtained at all in other ways. 

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