Exploring the Conversion of Macrocyclic 2,2′-Biaryl Bis(thioureas) into Cyclic Monothioureas: An Experimental and Computational Investigation

Macrocyclic bis­(thioureas) derived from 2,2′-biphenyl and binaphthyl skeletons have been synthesized by reaction of 2,2′-diaminobiaryl and 2,2′-bis­(isothiocyanato)­biaryl derivatives. The splitting of these bis­(thioureas) into two units of the respective cyclic monothioureas has been monitored by NMR, shedding some light on the factors that control these processes. Additionally, a computational study revealed up to three mechanistic paths for the conversion of the 2,2′-biphenyl-derived bis­(thiourea) into the corresponding monothiourea. The proposed mechanisms account for the participation of a molecule of water as an efficient proton-switch as well as for different classes of putative intermediates. The computational study also supports the ability of the thiourea group to participate in a plethora of processes, such as prototropic equilibria, sigmatropic shifts, heteroene and retro-heteroene reactions, and cis ⇆ trans isomerizations.