Synthesis of benzimidazo[2,1-b]benzothiazole derivatives through sequential Cu-catalyzed domino coupling and Pd-catalyzed Suzuki reaction

Visible light-promoted intermolecular cyclization/aromatization of chalcones and 2-mercaptobenzimidazoles via an EDA complex and a mechanism study

Visible-light-promoted cyclization and aromatization of chalcones with 2-mercaptobenzimidazoles have been successfully developed to obtain diverse imidazo[2,1-b]thiazoles, and C-S and C-N bonds were constructed in one step. The reaction uses oxygen in the air as an oxidant, and the method does not need an external photocatalyst or a transition metal catalyst. The strategy features mild conditions, a simple system, readily accessible feedstocks, and a friendly environment. UV absorption spectroscopy and control experiments have shown that the reaction mechanism involves the formation of an electron-donor-acceptor (EDA) complex from thiolate anions and chalcones. In order to verify the mechanism, we studied the structure and HOMO/LUMO of the EDA complex by density functional theory (DFT) calculations. The results show that the π-π stacking between chalcones and 2-mercaptobenzimidazoles will cause a red shift of the UV absorption wavelength in the presence of Cs₂CO₃, and also provide a theoretical basis for the electron transfer of EDA complexes.

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 KOt-Bu and CBrCl3 as radical initiator, benzo[d]imidazo[2,1-b]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)3, results in the regioselective nucleophilic attack at both carbonyl groups forming benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones instead.

Pd-catalyzed one-pot sequential unsymmetrical cross-coupling reactions of aryl/heteroaryl 1,2-dihalides

The present methodology allows the conversion of easily available aryl/heteroaryl 1,2-dihalides into synthetically useful unsymmetrically substituted arenes/heteroarenes in good to excellent yields under mild reaction conditions.

An efficient one pot three-component nanocatalyzed synthesis of spiroheterocycles using TiO2 nanoparticles as a heterogeneous catalyst

An efficient, environmentally benign isocyanide-based domino protocol is presented for synthesizing spiroheterocycles with 2-amino benzothiazole/1,3,4-thiadiazole, cyclohexyl/tert-butyl isocyanides and isatines/cyclic carbonyls, catalyzed by recyclable nanocrystalline TiO₂.