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, C13H13N3OS, and the intermediate metal complexes aquabis[5-methoxy-N-(pyridin-2-yl-kappa N)-1,3-benzothiazol-2-amine-kappa N-3] copper(II)dinitrate, [Cu(C13H11N3OS)(2)(H2O)](NO3)(2), and bis{2-[(5-methoxy-1,3-benzothiazol-2-yl)amino] pyridin-1-ium} dichloridogold(I)chloride monohydrate, (C13H12N3OS)(2)[AuCl2]Cl center dot H2O, are reported. The copper complex exhibits a distorted trigonal-bipyramidal geometry, with direct metal-to-benzothiazoleligand coordination, while the gold complex is a salt containing the protonated uncoordinated benzothiazole, and offers evidence that metal reduction (in this case, Au-III to Au-I) 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.