Synthesis of five- and six-membered cyclic guanidines by guanylation with isothiouronium iodides and amines under mild conditions

Cyclic guanidine hydroiodides were obtained in one step by the reactions of isothiouronium iodides with an equimolar amount of various amines in tetrahydrofuran. The obtained hydroiodides were neutralized with sodium hydroxide or anionic exchange resin to afford the corresponding substituted cyclic guanidines in quantitative yields.