Chemistry. The synthetic route usedl involved the acid-catalyzed (p-TSA or Pz05) intramolecular alkylation at the 2 position of the indole nucleus by a hemiketal 111, or a derived oxonium ion intermediate IV, formed in situ from the reaction of an indole-3-ethanol (tryptophol) I and a keto ester RlCORz I1 (see Table I for definitions of R1 and Rz). The 1, 3, 4, 9-tetrahydropyrano [3, 4-b] indole-l-alka-noic acid esters obtained from this reaction ...