A growing number of biologically and pharmaceutically relevant compounds incorporate the cyclic guanidine functionality.(1) Cyclic guanidines are also capable of catalyzing organic reactions(2) and exhibiting a variety of coordination modes and a range of donor properties leading to compatibility with a wide range of metal ions.(3) Therefore, their synthesis has been extensively explored. Generally, the known methods include (1) the reactions(4) of amines with S,S- ...