Synthesis of Cyclic Dipeptidyl Ureas via Ugi Three-Component Reaction

Significance

For the first time, semicarbazones are employed in the Ugi three-component reaction with isocyanates and α-keto acids to give 1,1-di­substituted semicarbazides. The products conveniently precipitate from solution under these reaction conditions. An X-ray crystal structure analysis was obtained of one adduct. Treatment with sodium ethoxide followed by methylation using diazo­methane affords [1,2,4]-triazine derivatives. The sequence appears to be of general value for the synthesis of such 6-oxo[1,2,4]triazin-1-yl derivatives.