Synthesis of Novel Thiazolo[2,3-b]pyrimidine Derivatives Catalyzed by Nano‑SiO2 as a Reusable Heterogeneous Catalyst

Thiazolo[2,3-b]pyrimidine is an important class of compounds with two different sulfur-nitrogen containing fused heterocycles, which specific strategies have beenreported for the synthesis of thiazolo[2,3-b]pyrimidine derivatives as follows: In 2014 Wu et al. synthesized this scaffold via the reaction of 2-aminobenzothiazole, aromaticaldehydes and 2-hydroxy-1,4-naphthoquinone in the presence of amberlyst-15 [1]. In 2017, Keshari et al. utilized a p-TSA-catalyzed domino approach for the synthesis ofnovel thiazolo[2,3-b]pyrimidines [2]. In addition, the field of silica nanocatalysis has attracted the attention of researchers working, because of their stability, high surface area, and non-toxicity which made the silica nanoparticles ideal candidates for catalyst support [3]. In the view of above-mentioned points, a new series of thiazolo[2,3-b]pyrimidines derivatives were designed and prepared, by the three-component reaction of 2- aminothiazole, aromatic aldehydes and 2-hydroxy-1-4-naphthoquinone in thepresence of nano‑SiO2 as a heterogeneous catalyst which used commercially (CABO- SIL M5) with characteristic properties in acetonitrile at room temperature (Scheme1). The direction of heterocyclization and the structure of final products identified spectroscopically. The significant advantages of this protocol include simplicity, regioselectivity, good yields, use of a recyclable catalyst and simple work-up.