New evidence for the presence of a spiroindolenine intermediate in Pictet–Spengler reaction of Nb-hydroxytryptamine
Abstract
The Pictet–Spengler reaction between Nb-hydroxytryptamine and cysteinals in the presence of trifluoroacetic acid gave, in addition to the normal products, β-carbolines (12)–(17), the unexpected tetracyclic compounds (4)–(9), providing new evidence for a spiroindolenine intermediate.