Synthesis of 2-Mercaptobenzothiazoles via Metal-Free Heteroannulation

Significance

Reported is a transition-metal-free tandem condensation-S-arylation reaction of o-haloanilines 1 and CS₂ leading to 2-mercaptobenzothiazole derivatives 2. In contrast to the previous results for the copper-catalyzed heteroannulation from the same group (F. Wang, P. Zhao, C. Xi Tetrahedron Lett. 2011, 52, 231), the catalyst (CuI) was found to be unnecessary for this transformation. After screening of bases and solvent, the conditions involving DBU as base and toluene as solvent were found to be optimal. The reaction does not proceed in absence of a base. A study of the substrate scope showed that o-haloanilines 1 with EDGs and EWGs were well tolerated, affording product 2 in good yield. Moreover, ortho- and para-substituted substrates also afforded high yields of 2-mercaptobenzothiazoles. It is noteworthy that o-chloroaniline was found to be unreactive. A plausible mechanism was proposed without evidence.