Copper(II)- and gold(III)-mediated cyclization of a thiourea to a substituted 2-aminobenzothiazole.

Benzothiazole derivatives are a class of privileged molecules due to their biological activity and pharmaceutical applications. One route to these molecules is via intramolecular cyclization of thioureas to form substituted 2-aminobenzothiazoles, but this often requires harsh conditions or employs expensive metal catalysts. Herein, the copper(II)- and gold(III)-mediated cyclizations of thioureas to substituted 2-aminobenzothiazoles are reported. The single-crystal X-ray structures of the thiourea N-(3-methoxyphenyl)-N'-(pyridin-2-yl)thiourea, CHNOS, and the intermediate metal complexes aquabis[5-methoxy-N-(pyridin-2-yl-κN)-1,3-benzothiazol-2-amine-κN]copper(II) dinitrate, [Cu(CHNOS)(HO)](NO), and bis{2-[(5-methoxy-1,3-benzothiazol-2-yl)amino]pyridin-1-ium} dichloridogold(I) chloride monohydrate, (CHNOS)[AuCl]Cl·HO, are reported. The copper complex exhibits a distorted trigonal-bipyramidal geometry, with direct metal-to-benzothiazole-ligand coordination, while the gold complex is a salt containing the protonated uncoordinated benzothiazole, and offers evidence that metal reduction (in this case, Au to Au) is required for the cyclization to proceed. As such, this study provides further mechanistic insight into the role of the metal cations in these transformations.