Fluorous synthesis of hydantoins and thiohydantoins.

[reaction: see text] A fluorous synthesis of hydantoins is introduced. The reaction of perfluoroalkyl (Rfh)-tagged amino esters with an isocyanate is followed by the cyclization of ureas and simultaneous cleavage of the fluorous tag to afford hydantoins. The product purification is performed by solid-phase extraction over FluoroFlash cartridges, and no fluorous solvent is involved in either the reaction or the separation processes. The same method applies to synthesis of thiohydantoins.