Support studies toward the hicksoane alkaloids reveal cascade reactions of a (tryptophanamido)methylglycinate

Abstract

Herein we report unanticipated results that emerged from a synthetic study targeting the unique triazocane present in the hicksoane alkaloids. An initial strategy focused on the cyclisation-ring expansion of a 3-(tryptophyl)imidazolidin-4-one failed due to the high reactivity of the imide unit; passing a methanolic solution of this compound through a weakly basic ion exchange resin led to methanolysis to form a (tryptophanamido)methylglycinate. Attempted lactamisation of this (tryptophanamido)methylglycinate led to the formation of a (tryptophyl)imidazolidin-4-one, a rare imidazopyrido[3,4-b]indolone and a β-carboline. Control reactions informed a mechanistic rationale for these cascade processes.