Synthesis of Five-Membered Cyclic Guanidines via Cascade [3 + 2] Cycloaddition of α-Haloamides with Organo-cyanamides.

The convenient preparation of N2-unprotected five-membered cyclic guanidines was achieved through a cascade [3 + 2] cycloaddition between organo-cyanamides and α-haloamides under mild conditions in good to excellent yields (up to 99%). The corresponding cyclic guanidines could be easily transformed into hydantoins via hydrolysis.