| Abstract: | Acid-Catalyzed Reactions of 2-Vinylaniline Derivatives with 1-Benzyl- and 1-Methylpiperidin-4-one: An Elegant Synthesis of New Polycyclic Indole Derivatives The reaction of 2-vinylaniline derivatives with 1-benzylpiperidin-4-one or 1-methylpiperidin-4-one in toluene at temperatures between 115 and 120° with toluene-4-sulfonic acid as catalyst leads in good yields to a new class of polycyclic indole derivatives (Scheme 1, Table 1). The structure of the new diastereoisomerically pure racemic compounds 1–5 is determined by NMR-spectroscopic methods. A reaction mechanism proceeding via cyclization of enamine 9 , leading to a racemic, tricyclic reactive intermediate 10 , and subsequent intramolecular 1,5-dipolar cyclization as key steps in proposed for the formation of octahydropyrido4′,3′:4]cyclobut1,2-b]indoles 1–5 . The scope and limitations of the new method are discussed (see Table 2). |
