The first Lewis base-catalysed allylic sulfuration of Morita–Baylis–Hillman (MBH) adducts derived from ketones (isatins) has been developed, which affords C3-quaternary oxindole derivatives bearing thio-group at 3-position in good to excellent yield (up to 98% yield) under mild reaction conditions. Significantly, the potential utility of the protocol also has been demonstrated by gram-scale synthesis of 3-alkylthio-2-oxindole (3ae), a low catalyst loading (0.3 mol %) and facile conversion of resulting product (3ad) into functionalized pyrrolidinone (5ad).