A pot-economical and green synthesis of novel (benzo[ d ]imidazo[2,1- b ]thiazol-3-yl)-2H-chromen-2-one in ethanol–PEG-600 under catalyst-free conditions

4‐Hydroxycoumarin: A Versatile Substrate for Transition‐metal‐free Multicomponent Synthesis of Bioactive Heterocycles

“…(Scheme 20). [74] Pleasingly, under catalyst‐free conditions, the desired products 67 derived from the PEG‐600 mediated multicomponent reaction of 4‐hydroxycoumarin 1 , 2‐aminobenzothiazole 66 , and arylglyoxal 53 , were obtained in 81–95% yield. By employing this operational simplicity, column‐free approach, a total of 26 compounds possessing the benzothiazole ring were synthesized.…”

“…This intermediate underwent aza‐Michael addition with 66 followed by cyclic condensation to furnish the intermediate X . Subsequent elimination of water from X , yield the final product 67 [74] …”

On water catalyst-free synthesis of benzo[d]imidazo[2,1-b] thiazoles and novel N-alkylated 2-aminobenzo[d]oxazoles under microwave irradiation

“…Most of the syntheses developed so far suffer serious drawbacks such as the use of transition metals, harsh reaction conditions, use of toxic solvents, long reaction times and limited substrate scope. [38][39][40][41][42] Therefore, it is warranted to devise a new strategy to construct these privileged scaffolds in a sustainable pathway, which forms the core of modern organic synthesis. The application of microwave (MW) irradiation together with green solvents has gained signicant attention in recent years because of the extremely rapid growth in the generation of products in non-ammable, nontoxic environments of green solvents.…”

Catalyst‐free one‐pot regioselective synthesis of benzo[d]imidazo[2,1‐b]thiazoles by heating or grinding

“…The synthesis of benzo[ d ]imidazo[2,1‐ b ]thiazoles has been reported by condensation of 2‐mercaptobenzimidazoles and ortho ‐dihaloarenes in presence of K 2 CO 3 at 130°C via domino coupling reactions, copper‐mediated coupling of 2‐iodobenzothiazole and 2‐iodoaniline, and FeCl 3 /ZnI 2 –mediated synthesis via cyclization of 2‐aminobenzothiazole and ketones . Recently, synthesis of benzo[ d ]imidazo[2,1‐ b ]thiazoles has been reported by condensation of 2‐aminobenzothiazole, arylglyoxal monohydrate, and 4‐hydroxycoumarin in ethanol‐PEG‐600 at 80°C . Synthesis of imidazothiazoles has been reported by reaction of 2‐aminobenzothiazoles and cyclic ketones in presence of elemental sulfur under metal‐free conditions, and synthesis of trisubsituted 1,3‐thiazoles has been reported via microwave‐assisted domino reaction of phenylglyoxal, thiobenzamide, and different active methylene group compounds …”