Diversified Aminohydantoins from Ureas and Thioureas Tethered to Amides.

Intramolecular cyclization of thioureas or ureas tethered to amides afforded 2-iminohydantoins and 2-amino-1H-imidazol-4(5H)-ones in very high yields (87–100 %) regardless of the substituent (alkyls or aryls). This reaction proceeds through carbodiimides and iminium ions as intermediates. Among the reagents used to generate the carbodiimides, CBr4/Ph3P, CCl4/Ph3P, O,O′-bis(2′-pyridyl)thiocarbonate, and HgO were investigated.