SO₄⁻²/SnO₂–catalyzed cyclocondensation for the synthesis of fully functionalized pyridines

Abstract

An efficient and promising synthetic approach to assemble skeletons of multifunctionalized pyridine derivatives in presence of recyclable heterogeneous sulfated tin oxide (STO) catalyst has been evolved. The STO catalyst was used as a promoter for the cyclocondensation process in ethanol at 70°C. Overall performance of this catalyst was attributed to the cooperative contribution of its Lewis and Brønsted-Lowry acidic sites. Nanosized STO catalyst was synthesized by using sol-gel process and characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), 1 H-NMR, and scanning electron microscopy (SEM). This catalyst tolerates most of the substrates, and protocol shows precious capabilities consist of high yields, operational simplicity, less reaction time, and eco-friendly conditions. The newly synthesized heterogeneous catalyst was easily separated and reused. All the reactions are carried out for subsequent cycles without significant loss of catalytic activity and with good proficiency.

An effective process for the synthesis of dihydropyridines via SO4−2/SnO2‐catalyzed Hantzsch reaction

“…In extension to our earlier effort towards finding new methods for construction of biologically active small heterocyclic molecules, STO was used as a recyclable solid catalyst. [ 38,39 ] Keeping these features in mind, we initially developed a model reaction of acetoacetanilide, ammonium hydroxide, and different aldehydes in the presence of STO (Scheme 1).…”

Applications of Sulfated Tin Oxide (STO) in Organic Synthesis - from 2016 to 2021

“…11 Varala and co-workers published STO-catalyzed cyclocondensation of the synthesis of fully functionalized pyridines from substituted aldehydes, malononitrile, aliphatic ketone and ammonium hydroxide in ethanol at 70 °C (Scheme 4). 12 Due to cooperating contribution of its Lewis and Brønsted acidic sites, as shown in Figure 1, efficacy of the catalyst is enhanced. Nano sized STO catalyst is compatible with several substrates and reusable.…”

Synthesis of β-amino alcohols by ring opening of epoxides with amines catalyzed by sulfated tin oxide under mild and solvent-free conditions

“…Due to its low cost, greater stability, non-corrosive nature, reuse and recyclability, high efficiency, and large surface area, sulfated tin oxide (STO, SO4 -2 /SnO2) has emerged as an effective and commercial catalyst. It is used extensively in chemical and industrial applications, [29][30][31][32][33][34][35][36] consisting of both sulfated and sulfonic acid moiety on heterogeneous solid bases.…”