The synthesis of dihydrocorynantheol (5) and of the pentacyclic Strychnos alkaloid tetrahydroakuammicine (4) is reported from 5-ethyl-N-hydroxyethyl-2-(1-phenylsulfonyl-3-indolyl)-4-piperidineacetates (1) by means of a K(t)OBu/BF3.Et2O intramolecular cyclization.