Practical and efficient synthesis of tetrahydrobenzo[b]pyran using caffeine supported on silica as an ionic liquid solid acid catalyst

The new catalyst silica-caffeine hydrogen sulfate [SiO2-caff.]HSO4 was conveniently prepared from commercially available 3-chloropropyltriethoxysilane via immobilization on silica followed by reaction with caffeine. The catalyst prepared was then characterized by the FT-IR spectroscopy, TGA, EDX, and SEM techniques. It was found that this heterogeneous catalyst was a highly efficient one for the synthesis of tetrahydrobenzo[b]pyrans in good-to-high yields, and could be recovered by a simple filtration of the reaction solution and reused for five consecutive runs. The attractive features of this method are simple procedure, clean reaction, easy work-up, use of a reusable catalyst, and performing a multi-component reaction.