The pictet-spengler reaction of Nb-hydroxytryptamines and cysteinals. I. Isolation of tetracyclic intermediates and formation of optically active Nb-hydroxy-tetrahydro-β-carbolines.
The Pictet–Spenglerreaction 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 newevidence for a spiroindolenineintermediate.