Synthesis of Bicyclic and Tricyclic Chiral Guanidinium Salts by an Intramolecular Alkylation Approach

Synthetic studies leading to three new types of chiral guanidinium scaffolds are described. Structures of interest include bicyclic guanidine derivatives with various substitution patterns around the guanidine core, as well as a highly rigid tricyclic scaffold. The challenging targets were accessed by application of mercury(II)‐promoted guanylation of N‐Boc‐substituted thioureas and Ishikawa's desulfurative cyclization. In addition to our synthetic logics, a scalable synthesis of the tricyclic guanidinium salt is presented. Syntheses of three new types of chiral guanidinium salts are described. The structures of interest possess highly rigid bi‐ and tricyclic scaffolds. They were assembled by means of two different guanylation methods followed by inter‐ or intramolecular alkylation of the guanidine core.