The Hg(OTf)2-catalyzed cyclization of N-tosylanilinoallylic alcohols giving rise to vinyl-substituted indolines has been developed. The reaction takes place with a highly efficient catalytic turnover (up to 1000 times) under mild conditions. The hydroxyl group of the organomercuric intermediate is protonated by in situ formed TfOH generating an oxonium cation, which regenerates the catalyst after demercuration.