Amino Acid Salts Catalyzed Asymmetric Aldol Reaction of Tryptanthrin: A Straightforward Synthesis of Phaitanthrin A and Its Derivatives

The first asymmetric synthesis of (S)-Phaitanthrin A and its derivatives via a catalytic aldol reaction of Tryptanthrin and ketones is described, in which the cheap, easily prepared natural amino acid salts exhibited unique catalytic ability; importantly, this methodology tolerates a range of substrates with different substitution patterns. Moreover, the synthetic utility of this strategy was further illustrated by a gram-scale synthesis of Phaitanthrin A.