Green synthesis of spiro[indoline-3,90-xanthene]trione derivatives using sulfonic acid functionalized SBA-15 as a new nanoporous acid catalyst

A simple and efficient method for the synthesis of spiro[indoline-3,90-xanthene]trione derivatives has been achieved through the condensation reaction of isatins and two moles of dimedone or 1,3-cyclohexanedione, under solvent-free conditions, in the presence of SBA-15-PrSO3H as an efficient heterogeneous nano solid acid catalyst. The features of this procedure are short reaction times, good yields, solvent-free reaction conditions, and simple workup. The absence of solvent allows avoiding the use of toxic organic solvents, which makes this reaction safe and environmentally friendly. Furthermore, the use of SBA-15-PrSO3H with a pore size of 6 nm has the advantage of being a nano-reactor in whose nanopores the reaction proceeds easily.