The Pictet-Spengler reaction, in which beta-arylethylamine is heated in the presence of an aldehyde to give an isoquinoline, is implented in synthesis of beta-carbolines, where an indole reacts with carbonyl compounds.
The reaction is seem to be catalyzed almost always in acid. However, I found a reaction (taken from a paper, see the image file) in which tryptamine reacts with glyoxylic acid in the presence of potssium hydroxide (KOH) to give a beta-carboline with an acid functional group, without any decarboxylation.
I have two questions:
1) What are the differences bewteen the acid-catalyzed mechanism and the base-catalyzed one? I wonder whether the base is added here only for pH-balancing (because the glyoxylic acid decreases pH, of course...)
2) Why a decarboxylation doesn't occur in this incident?
Enclosed herewith the acid-catalyzed mechanism which I've proposed...I would be very pleased if you find the base-catalyzed one.
Thank you very much indeed!