‘On water’ Knoevenagel condensation of isatins with malononitrile

Grinding of isatins with malononitrile in the presence of 1–5 equiv. of water for 15 min at room temperature affords the corresponding (2-oxo-1,2-dihydro-3H-indol-3-ylidene)malononitriles, the Knoevenagel condensation products, in 89–99% yields.