Synthesis of Tetrahydro-β-carbolines by a Manganese-Catalysed Oxidative Pictet-Spengler Reaction

Herein, an efficient and green procedure for the synthesis of tetrahydro-beta-carbolines via dehydrogenative coupling of alcohols with tryptamines is reported. The reaction was carried out under mild conditions in the presence of a catalytic amount of the (PNP)-P-iPr Mn catalyst and a weak base (Na2CO3). This method tolerated a variety of benzylic and aliphatic alcohol substrates with different functional groups and afforded diverse products in good to excellent isolated yields using tryptamines. Using this strategy, we successfully synthesised pharmaceutical molecules harman, harmaline, and harmine in a concise manner.