Rationalization of Benzazole-2-carboxylate versus Benzazine-3-one/Benzazine-2,3-dione Selectivity Switch during Cyclocondensation of 2-Aminothiophenols/Phenols/Anilines with 1,2-Biselectrophiles in Aqueous Medium

Abstract

The cyclocondensation reaction of 2-aminothiophenols with 1,2-biselectrophiles such as ethyl glyoxalate and diethyl oxalate in aqueous medium leads to the formation of benzothiazole-2-carboxylates via the 5-endo-trig process contrary to Baldwin’s rule. On the other hand, the reaction of 2-aminophenols/anilines produced the corresponding benzazine-3-ones or benzazine-2,3-diones via the 6-exo-trig process in compliance with Baldwin’s rule. The mechanistic insights of these cyclocondensation reactions using the hard–soft acid–base principle, quantum chemical calculations (density functional theory), and orbital interaction studies rationalize the selectivity switch of benzothiazole-2-carboxylates versus benzazine-3-ones/benzazine-2,3-diones. The presence of water facilitates these cyclocondensation reactions by lowering of the energy barrier.