Carbon–SO3H: a novel and recyclable solid acid catalyst for the synthesis of spiro[4H-pyran-3,3′-oxindoles]

Abstract A bioglycerol derived carbon-sulfonic acid is found to catalyze efficiently the three-component one-pot condensation of isatin, malononitrile, and 1,3-dicarbonyls to afford a wide range of spiro[4H-pyran-3,3′-oxindole]derivatives in good yields and selectivity. The use of a recyclable solid acid catalyst makes this method simple, convenient, and cost-effective.