Neighboring group participation of the indole nucleus: An unusual DAST-mediated rearrangement reaction
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.
Hallett
DJ
Merck & Co., Inc., 126 East Lincoln Avenue, Rahway, New Jersey 07065, USA.
Gerhard
U
Goodacre
SC
Hitzel
L
Sparey
TJ
Thomas
S
Rowley
M
Ball
RG