Weinreb amide as an efficient reagent in the one pot synthesis of benzimidazoles and benzothiazoles

A comprehensive review in current developments of benzothiazole-based molecules in medicinal chemistry

“…Other general methods include the microwave mediated reaction of o-aminothiophenol with bchlorocinnamaldehydes, the reaction of dibenzyl disulfides with oaminothiophenol, reduction of o,o 0 -dinitrodiphenyl disulfide, the reaction of S-aryl thiobenzoate with arylhaloamines, from 1,2,3-benzodithiazole-2-oxides, radical cyclization of benzyne intermediates, and Grignard reactions of arylisothiocyanates [45]. A number of catalysts, namely, (pmIm)Br [46], I 2 [47], ZrOCl 2 .8H 2 O [48], TMSCl [49], H 2 O [50], PCC [51], CAN [52], nano ceria (CeO 2 ) [53], cyanide [54], boron trifluoride etherate [55], mesoporous CdS nanospheres [56], silica supported nano-copper(II) oxide [57] and many more can also be used effictly used as catalysts to prepare BTA derivatives Fig. 3.…”

Recent Advances in the Chemistry and Biology of Benzothiazoles

“…One of such reagents is Weinreb amide reagent. An efficient one pot synthetic protocol for the synthesis of 2‐substituted benzothiazoles 151 has been reported by Sadashiva and co‐workers through condensation and cyclization of Weinreb amide 151 with o ‐aminothiophenol 150 . Chemically, Weinreb amide is N ‐methoxy‐ N ‐methylamide and it is very easy to prepare and has good stability and selectivity.…”

Water extract of onion catalyst: An economical green route for the synthesis of 2‐substituted and 1,2‐disubstituted benzimidazole derivatives with high selectivity

“…The well‐known and exploited route to benzimidazole 3 involves the direct condensation of 1,2‐diamines 1 with aldehydes 2 or carboxylic acids in the presence of strong dehydrating agent like H 2 SO 4 12 . Other improved procedures have also been subsequently reported which include reductive cyclization reaction of o ‐nitroaniline with aldehyde, palladium catalyzed tandem carbonylation‐cyclization reaction 13 and the reaction of aldehydes 2 with 1,2‐diamines 1 in the presence of catalysts such as trifluoroacetic acid, 14 TiCl 4 .SiO 2 , 15 Bi(OTf) 3 , 16 Bi(NO 3 ) 3 , 17 TMSCl, 18 ZnO‐NPs, 19 L‐ proline, 20 Fe(ClO 4 ) 3 , 21 solvent free SiO 2 /ZnCl 2 , 22 Fe 3 O 4 @SiO 2 @(NH 4 ) 6 Mo 7 O 24 , 23 SDS micelles, 24 CAN, 25 Cu(OTf) 2 , 26 Phospho sulfonic acid, 27 ZrOCl 2 .nH 2 O/montmorillonite K10, 28 montmorillonite K‐10, 29 NaPTSA, 30 DBSA, 31 Alumina‐sulfuric acid, 32 γ‐Fe 2 O 3 @SiO 2 NPs, 33 RuCl 2 (PPh 3 ) 3 , 34 Lewis acidic ionic liquids, 35 CoCl 2 .6H 2 O, 36 PSFSI/SBA‐15, 37 FeCl 3 ‐PANI, 38 Sm(OTf) 3 , 39 Na 2 S 2 O 5 , 40 In(OTf) 3 , 41 microwave irradiation, 42 1‐heptanesulfonic acid sodium salt, 43 and BF 3 ·OEt 2 44 . Unluckily, many of these are have major or minor limitations such as employing considerable amounts of toxic solvents, drastic reaction conditions, highly expensive catalyst and some of the metal based Lewis acid catalyzed reactions toxic to the environment.…”