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

Abstract

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.

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.…”

Synthesis of pyrimido[2,1-b][1,3]benzothiazoles and [1,3]benzothiazolo[3,2-a]quinazolines via one-pot three-component reactions from 2-aminobenzothiazole, arylglyoxals and 1,3-dicarbonyl compounds

“…Most of the methods depict syntheses of pyrimido[2,1-b] [1,3]benzothiazole and [1,3]benzothiazolo [3,2-a]quinazoline derivatives from intermolecular cyclization of 2-aminobenzothiazoles with malonic ester derivatives, 2,12 Meldrum's acid, 13 and β-ketoesters. 14 The reaction of 2-aminobenzothiazoles with various Michael acceptors, such as acetylenic compounds, 15,16 alkyl malonates, 8,17 and enaminones. 18 Moreover, organic and medicinal chemists have developed a series of multicomponent reactions (MCRs) for the synthesis of heterocyclic compounds and complex biologically-active compounds, [19][20] such as multi-component reaction of 2-aminobenzimidazole, benzaldehyde derivatives, and active methylene compounds, 6,[21][22] and various other methods.…”

Cu‐Catalyzed Synthesis of 4H‐benzo[4,5]thiazolo[3,2‐a]pyrimidin‐4‐ones: Molecular Docking Studies and Anti‐Proliferative Activities Against HepG2 Hepatocellular Carcinoma Cells

“…[42] Due to the great importance of pyrimidobenzothiazoles, several useful synthetic routes for the preparation of these compounds have been established. [43] The reported methods towards the synthesis of these scaffolds rely on the addition of alkynoic acid to 2-aminobenzothiazoles followed by the ring closure reaction, [30,31,35,44] the one-pot three components reaction of 2-aminobenzothiazole, carbonyl compounds and active methylene group containing moieties, [45] as a Lewis acid such as In(OTf) 3 catalyzed reaction between 2-aminobenzoxazoles and β-ketoester moiety, [46] the condensation of 2-aminobenzothiazoles and diethyl ethoxymethylenemalonate, [47] the ionic liquid e. g. 1-butyl-3-methylimidazolium bromide mediated reaction of 2-aminobenzothiazoles with Meldrum's acid and trimethylorthoformate, [48] the green reaction between 2-aminobenzothiazoles with isatin and cyclic 1,3-diketones in aqueous medium, [49] the reaction of 2-aminobenzothiazoles and epichlorohydrin, [50] the Biginelli one-pot three-component reaction of 2-aminobenzothiazoles, benzaldehyde derivatives and βketoesters or 1,3-diketones. [51] Recently, Beifuss and co-workers reported the synthesis of pyrimidobenzothiazoles from the reaction of catechol and 2,3-dihydro-2-thioxopyrimiden-4(1H)ones using Laccase catalyst.…”