A chiral complex derived from (S)-difluorophos and Hg(OTf)2 is identified as a powerful catalyst for the Sakurai-Hosomi reaction of isatins with allyltrimethylsilane, allowing the facile synthesis of valuable building blocks 3-allyl-3-hydroxyoxindoles in up to 97% ee, with only 0.5-1.0 mol% of catalyst loading.