Neighboring Group Participation of the Indole Nucleus: An Unusual DAST-Mediated Rearrangement Reaction
journal contributionposted on 19.07.2000, 00:00 by David J. Hallett, Ute Gerhard, Simon C. Goodacre, Laure Hitzel, Timothy J. Sparey, Steven Thomas, Michael Rowley, Richard G. Ball
A rearrangement reaction involving the indole nucleus was investigated using stereochemical markers and low-temperature NMR experiments. Treatment of (3S,4S)-3-hydroxy-4-(2-phenyl-1H-indol-3-yl)-piperidine-1-carboxylic acid benzyl ester (>90% ee) with diethylaminosulfur trifluoride gave stereospecifically (3S,4S)-4-fluoro-3-(2-phenyl-1H-indol-3-yl)-piperidine-1-carboxylic acid benzyl ester (>90% ee) with complete regioselectivity. The initial formation of a reactive spirocyclopropyl-3H-indole intermediate is believed to be responsible for the stereo- and regiochemical outcome of the reaction.