Revealing the Unique Role of Water in the Formation of Benzothiazoles: an Experimental and Computational Study.

Abstract

We present here a joint experimental and computational study on the formation of benzothiazoles. Our investigation reveals a green protocol for accessing benzothiazoles from acyl chlorides using either water alongside a reducing agent as the reaction medium or in combination with stoichiometric amounts of a weak acid, instead of the harsh conditions and catalysts previously reported. Specifically, we show that a protic solvent, particularly water, enables the formation of 2-substituted benzothiazoles from N-acyl 1,2-aminothiophenols already at room temperature, without the need for strong acids or metal catalysts. DFT Molecular Dynamics simulations coupled with advanced enhanced sampling techniques provide a clear understanding of the catalytic role of water. We demonstrate how bulk water - due to its extended network of hydrogen bonds and an efficient Grotthuss mechanism - provides a reaction path that strongly reduces the reaction barriers compared to aprotic environments, namely more than 80 kJ/mol for the first reaction step and 250 kJ/mol for the second. Finally, we discuss the influence of different aliphatic and aromatic substituents with varying electronic properties on chemical reactivity. Besides providing in-depth mechanistic insights, we believe that our findings pave the way for a greener route toward an important class of bioactive molecules.