Formation of dihydrouracils via cyclization of N-substituted 3-thioureidopropanoic acids and facile desulfurization

Cyclization of N-3 substituted 3-thioureidopropanoic acids in isobutyric anhydride at high temperature resulted in the unexpected formation of N-3,N-1-substituted dihydrouracils, as confirmed by thorough spectroscopic characterization. A mechanism based on the identification of intermediates observed at lower reaction temperatures is proposed.

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