Conjugate-Base-Stabilized Brønsted Acids: Catalytic Enantioselective Pictet–Spengler Reactions with Unmodified Tryptamine
摘要:
A conjugate-base-stabilized Bronsted acid facilitates catalytic enantioselective Pictet-Spengler reactions with unmodified tryptamine. The chiral carboxylic acid catalyst is readily assembled in just two steps and enables the formation of beta-carbolines with up to 92% ee. Achiral acid additives or in situ Boc-protection facilitate catalyst turnover.