An efficient synthesis of 2-arylbenzothiazoles using silica sulfuric acid, oxalic acid and aluminum chloride hydrate as heterogeneous and homogeneous catalyst systems

Abstract

A convenient method for the synthesis of 2-arylbenzothiazoles from condensation of aromatic/heteroaromatic aldehydes with 2-aminothiophenol has been developed using inexpensive, green and reusable solid acids -silica sulfuric acid (SSA), oxalic acid or AlCl 3 ·6H 2 O as efficient catalysts. The reactions occurred under mild conditions to afford the corresponding 2-arylbenzothiazoles in good to excellent yields.

1,3-Dibromo-5,5-dimethylhydantoin catalyzed one-pot synthesis of 2-arylbenzothiazoles

“…The pure solid products were obtained by recrystallization from ethanol. 13 We are pleased to acknowledge the financial support from Xinxiang Medical University.…”

“…When aromatic aldehydes were replaced by heteroaromatic aldehydes, the corresponding products were obtained with high yields as well. All of the structures were characterized by 1 H NMR, 13 C NMR and elemental analysis.…”

“…NMR (CDCl 3 ): 8.26-8.19 m, 1 H (Ar-H); 8.15 d, 1 H, J = 8.0 (Ar-H); 7.98 d, 1 H, J = 7.6 (Ar-H); 7.56-7.51 m, 2 H (Ar-H); 7.46-7.35 m, 3 H (Ar-H) 13. C NMR (CDCl 3 ): 166.4, 154.2, 137.1, 133.4, 132.6, 132.0, 131.5, 130.3, 127.0, 126.6, 125.8, 122.9, 121.8.…”

“…In additions, 2-arylbenzothiazoles is also a privileged scaffold in drug discovery 12 . One of the most practically and widely used routes for the synthesis of these compounds is the direct condensation of the 2-aminothiophenol with aldehydes, carboxylic acids, or their derivatives in the presence of various promoting agents, such as oxalic acid 13 , sulfuric acid immobilized on silica 14 , ceric ammonium nitrate 15 24 , methanesulfonic acid/SiO 2 25 , silica gel 26 , I 2 27 , Sc(OTf) 3 28 . However, most of these methods have following drawbacks: high thermal conditions, long reaction times, low yields of the products, harsh reaction conditions, and the use of toxic metallic compounds that result in waste streams.…”

Aromatization of 1,3,5-Trisubstituted of 4,5-Dihydro-1H-Pyrazoles by In-Situ Generation of I+from Hydrogen Peroxide/Acids/Iodide Potassium or Sodium Systems

“…[45][46][47][48][49][50][51][52][53][54][55] The salient catalytic activities attributed to silica sulfuric acid have encouraged us, in the second part of the present paper, to use various solvents like CH 3 CN, MeOH, H 2 O, EtOH, EtOAc, CH 2 Cl 2 and CCl 4 used for aromatization of 1,3,5-triphenyl-2-pyrazolines (1a) as model reaction, EtOH:H 2 O (10:1, v/v) was the solvent of choice as best results in terms of the yield was obtained using SSA (0.02 g), H 2 O 2 (1 mL) and KI (0.016 g) for 1 mmol of 1,3,5-triphenyl-2-pyrazolines when the reaction was run at 80 o C for 15 min in 90% yield (Table 3). Similarly, to illustrate the scope and usefulness of this methodology, a number of reactions were conducted (Scheme Literature data.…”