Synthesis of 13-Membered Ring L-Bitryptophanes and Their Enantioselective Indole Friedel-Crafts Reactions

A novel kind of framework containing axial 5-OH L-bitryptophane was synthesized under the mild reaction conditions. This synthetic strategy provides an efficient method to construct axial catalysts based on the new framework, which can be easily and economically separated from each other using silica gel column chromatography because the coupling products were atropisomers. For its promising application of the framework, eight catalysts were prepared and the relationship of the different catalytic centers on the enantioselectivity was tested using known and widely used model reactions and good enantiomeric ratios were recorded. Quantum methods were applied for the absolute configurations assignment of the new framework, the transition states (TSs) calculations for reaction mechanism study. The theoretical results agree well with the experiments. One best catalyst 8B with a 13-membered ring was found in the model reaction.