The Chiral Pool in the Pictet–Spengler Reaction for the Synthesis of β-Carbolines

The Pictet–Spengler reaction (PSR) is the reaction of a β-arylethylamine with an aldehyde or ketone, followed by ring closure to give an aza-heterocycle. When the β-arylethylamine is tryptamine, the product is a β-carboline, a widespread skeleton in natural alkaloids. In the natural occurrence, these compounds are generally enantiopure, thus the asymmetric synthesis of these compounds have been attracting the interest of organic chemists. This review aims to give an overview of the asymmetric PSR, in which the chirality arises from optically pure amines or carbonyl compounds both from natural sources and from asymmetric syntheses to assemble the reaction partners.