An Organocatalytic Pictet-Spengler Reaction in Total Synthesis

Significance

A concise six-step total synthesis of (-)-arboricine is reported, a natural product originally isolated from leafs of Kopsia arborea. The key step of the reported approach is an organocatalytic phosphoric acid 1-catalyzed Pictet-Spengler reaction of a tryptamine derivative, affording the desired β-carboline intermediate in high yield and enantioselectivity. The furnished stereocenter later sets the stage for a diastereo­selective Pd-catalyzed cyclization, giving rise to the desired product in an overall yield of 33%.