Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and β-ketoamides.

Two regiodivergent approaches to intermolecular cyclization of 2-aminobenzothiazoles with β-ketoesters and amides have been developed, controlled by the reagents employed. With the Brønsted base KOBu and CBrCl as radical initiator, benzo[]imidazo[2,1-]thiazoles are synthesized via attack at the α-carbon and keto carbon of the β-ketoester moiety. In contrast, switching to the Lewis acid catalyst, In(OTf), results in the regioselective nucleophilic attack at both carbonyl groups forming benzo[4,5]thiazolo[3,2-]pyrimidin-4-ones instead.