Synthesis and Mechanistic Study of Triheterocyclic 4H‐Pyrimido[2,1‐b]benzothiazole derivatives, One‐Pot Three‐component Reaction under Solvent‐Free Conditions

Abstract

An efficient method has been developed for the preparation of 4H‐pyrimido[2,1‐b]benzothiazole derivatives by the condensation of aldehydes, β‐ketoester, and 2‐amino benzothiazole under solvent and solvent‐free conditions using various catalysts. The reaction uses benzothiazole as a new component, and good yield is obtained at 60–65°C under solvent‐free conditions. Atom economies, good yield, environmentally benign, and easy to work‐up are some of the important features of this protocol. The present study suggests that acetic acid and metal catalysts follow different mechanism. In acetic acid, 2‐amino benzothiazole reacts with benzaldehyde, and resultant intermediate reacts with ethyl acetoacetate to give final product, whereas in the presence of metal catalysts, 2‐amino benzothiazole first reacts with ethyl acetoacetate, and resultant intermediate reacts with benzaldehyde to give pyrimido[2,1‐b]benzothiazole.

TiO2/porous carbon as a new nanocomposite and catalyst for the preparation of 4H-pyrimido[2,1-b]benzimidazoles

“…In a suggested mechanism, which is supported by the literature, 5–25,41 ethyl acetoacetate reacted with aldehyde which is activated by TiO 2 /PCN to prepare intermediate (I). Then, 2-aminobenzimidazole is reacted with intermediate (I) to give (II).…”

“…Preventing the loss of energy, materials and solvent are some other advantages of this protocol. [6][7][8][9][10][11][12][13] Multi-component synthesis of 4H-pyrimido[2,1-b]benzazoles was reported using various catalysis such as, nano-[Co-4CSP] Cl 2 , 5 iron uoride, 14 Fe 3 O 4 @nano-cellulose/TiCl, 15 chitosan, 16 nano-Fe 3 O 4 @SiO 2 -TiCl 3 , 17 H 3 PO 4 -Al 2 O 3 , 18 nano-TiCl 2 /cellulose, 19 acetic acid, 20 TMGT, 21 1,3-disulfonic acid imidazolium triuoroacetate, 22 [bmim]BF 4 , 23 GO@PSA-Cu 24 and poly (vinylpyrrolidonium) perchlorate. 25 Due to importance of 4H-pyrimido[2,1-b]benzimidazoles, the nd of the more efficient method for the preparation of these signicant compounds are still needed.…”

α-Aminoazoles/azines: key reaction partners for multicomponent reactions

“…An interesting case was studied by P. K. Sahu and coworkers, 32 where the synthesis of these pyrimidine derivatives was achieved in the presence of a solvent and under solvent-free conditions using various catalysts. When the condensation among 2-amino benzothiazole 3b, aldehydes 4 and β-ketoester 7 was carried out in the presence of acetic acid as the catalyst and methanol as the solvent at 65 °C, the corresponding products were obtained after 12–20 h. Conversely, the same reaction was completed in 70–120 min when carried out with various metal catalysts under solvent-free conditions.…”

Fe3O4@nano-cellulose/Cu(ii): a bio-based and magnetically recoverable nano-catalyst for the synthesis of 4H-pyrimido[2,1-b]benzothiazole derivatives

“…14 Pyrimido[2,1-b]benzothiazole derivatives were synthesized through multicomponent reaction between 2-amino benzothiazole, aromatic aldehydes and b-ketoesters. [15][16][17][18] Previously, this protocol has been catalyzed by iron uoride, 19 pyridine, 11 acetic acid, 20 1,1,3,3-N,N,N 0 ,N 0 -tetramethylguanidinium tri-uoroacetate (TMGT), 16 tetrabutylammonium hydrogen sulfate (TBAHS), 17 N-sulfonic acid modied poly(styrene-maleic anhydride) (SMI-SO 3 H), 21 chitosan, 18 aluminum trichloride 22 and Fe 3 O 4 @nano-cellulose/TiCl. 23 Some of the reported protocols have harsh conditions and long reaction times.…”