Indoles, III Lactamisation of 4.9‐Dihydropyrano [3.4‐<i>b</i>]indol‐1(3<i>H</i>)‐ones. ‐ A New Synthetic Route to the β‐Carboline Ring System

Abstract

Abstract Reaction of the pyrano[3.4‐ b ]indolones 1a‐d with aniline, benzylamine, phenylethylamine and propylamine at 200–210 °C yields the 2.3.4.9‐tetrahydro‐1 H ‐pyrido[3.4‐ b ]indol‐1‐ones 5a‐j , which can be converted to the 2.3.4.9‐tetrahydro‐1 H ‐pyrido[3.4‐ b ]indoles 6a‐j by reduction with LiAlH 4 . After treatment with methylamine and 2 only the amides 3 and 4 could be isolated. Unsubstituted tetrahydro‐β‐carboline 7 is available by regioselective debenzylation of 6c .