An Efficient One‐Step Synthesis of Piperidin‐2‐yl and Pyrrolidin‐2‐yl Flavonoid Alkaloids through Phenolic Mannich Reactions
An efficient one-step synthesis of piperidin-2-yl and pyrrolidin-2-yl flavonoid alkaloids was achieved in good to excellent yields by a highly regioselective phenolic Mannich reaction of chrysin with cyclic imines or iminium salts. Performing the reaction in a mixture of H2O/THF in the absence of an external reagent afforded the C-6 alkylated product exclusively. The same reaction in water in the presence of NaOH provided the C-8 alkylated flavonoid as a major product. The reaction has been successfully extended to simple phenols.