Cyclic ureas were successfully synthesized from alkenyl isoureas comprising a tosyl group (Table ). For example, when cobalt complex C1 was used, the 6-membered ring 18a formed. Although the synthesis of the 7-membered ring 18b with C1 resulted in a low yield, the yield improved to 79% by changing the catalyst to cobalt catalyst C6. The 8-membered ring 18c was not obtained when cobalt catalyst C6 was used. Note that the Ns and TFA groups are superior to the Ts group if a deprotection step is required. As a comparison, we discovered that unusual cyclic isoureas can be selectively obtained when using alkenyl urea as a starting material. Alkenyl ureas were synthesized from alkenyl amine and cyclized immediately without purification owing to the instability of the intermediate during silica gel purification. Table S-containing heterocycles are found in biologically active compounds such as biotin and other pharmaceuticals. The concept of deprotective cyclization to develop an intramolecular hydrothiolation affording S-containing heterocycles was next applied. Compared with hydroamination (C-N bond formation) and hydroalkoxylation (C-O bond formation), hydrothiolation has been reported in only three cases. No results on substrate generality can be found. Alkenyl thiols are unstable compounds owing to non-selective cyclization (five-and sixmembered rings) and spontaneous oxidation to disulfides. This potential instability of alkenyl thiols could be a reason why the development of intramolecular reactions has been hindered. Therefore, several starting materials with protected thiol groups were synthesized and MHAT/RPC-promoted cyclization was attempted by We group. Using benzoyl thioesters resulted in an acceptable yield, and the p-methoxybenzoyl group showed no significant decrease in reactivity when the quantity of catalyst was reduced in the transformation from 19a to 20a (Table ). Substrate generality was investigated using the optimized protective group, and various Scontaining heterocycles (20b-20d) were also successfully synthesized.