Acidic and Basic Supported Reagents for One-Pot Synthesis of Benzo[b]thiophenes

Significance

Silica gel-supported sodium carbonate (SiO₂-Na₂CO₃) and silica gel-supported polyphosphoric acid (SiO₂-PPA) were demonstrated to be able to coexist in the same vessel and function as a base and an acid, respectively. The synthesis of benzo[b]thiophenes was chosen as a model for the two-step reactions in one pot using the inorganic solid-supported acid and base. The supporting reagents SiO₂-Na₂CO₃ and SiO₂-PPA were prepared from Wakogel C-200 with Na₂CO₃ and PPA, respectively. The reaction of 3-bromo-4-phenyl butane-2-one with thiophenol was carried out in the presence of SiO₂-Na₂CO₃ and SiO₂-PPA in chlorobenzene to give 2-benzyl-3-methylbenzo[b]thiophene 4a in 80% yield. Base-promoted S-alkylation to produce α-phenylthio ketone 3 and acid-catalyzed dehydrative ring closing to give 4a took place in one pot, successively.