Chemoselective synthesis of 2-aryloxazines and 2-aryltetrahydropyrimidines using nano-SiO2 as a reusable solid acid catalyst under thermal conditions and microwave irradiation

Determination of the promoting effect of nano SiO2and H3PO4@nano SiO2in the thiocyanation ofN-containing aromatic compounds under solvent-free conditions

“…[16][17][18] SiO 2 nanoparticles (SiO 2 NPs) have been a focus of extensive research in the catalyst field due to their chemical stability, large surface area, non-toxicity (LD50: 20,800 mg/kg), reasonable cost, and environmentally friendliness in the context of green synthesis. [19][20][21] Furthermore, nanometer silicon dioxide (nano SiO 2 ) has played a catalytic role in a wide range of transformations such as 2-aryloxazines and 2-aryltetrahydropyrimidines synthesis, [22] synthesis of 3-oxo-3-phenylpropanamid derivatives, [23] bis-Michael addition of active methylene compounds to conjugated alkenes, [24] synthesis of 4H-pyrans and polysubstituted aniline derivatives, [25] synthesis of thioethers, thioesters, vinyl thioethers, and thio-Michael adducts, [26] synthesis of 2-hydroxyacetamide, [27] and synthesis of 2,3-dihydro-1H-isoindolones. [28] In continuation of our research interest on the thiocyanation of (hetero)aromatic organics, [29][30][31][32] herein we report nano SiO 2 as a commercially available, low-cost and non-oxidative promoter for the thiocyanation of some N-containing heteroaromatics and N-activated arenes in the presence of NH 4 SCN at 70°C under solvent-free conditions (Scheme 1 and Table 2).…”