In 2014, we reported that intramolecular hydroamination proceeds via the MHAT/RPC mechanism. When alkenyl sulfonylamides and other compounds are used as starting materials, various nitrogen-containing heterocycles can be constructed via nucleophilic attack of the nitrogen atom. Next, we applied the MHAT/RPC mechanism to the synthesis of cyclic guanidines commonly found in natural marine products. This practical method characterized the availability of Cbz and Boc as common protective groups. The protective groups reduce the polarity of the product and facilitate purification and enable easy deprotection. Furthermore, owing to the ease of the MHAT/RPC mechanism, we synthesized novel medium-membered cyclic guanidines.