Investigation of the configurational stability of lithiated phosphineoxides using the Hoffmann test: X-ray structures of(2S*,3S*,4R*)-2-(N,N-dibenzylamino)-4-diphenylphosphinoyl-1-phenylpentan-3-ol and(2S*,4S*)-2-(N,N-dibenzylamino)-4-diphenylphosphinoyl-1-phenylpentan-3-one
1997
The Hoffmann test (reaction of a racemic organolithium
with a phenylalanine-derived aldehyde) is used to show that
lithiated diphenylphosphine oxides are not configurationally
stable in THF at -78 °C (usual reaction
conditions) on the timescale of their rate of reaction with the
aldehyde. The test is carried out by reacting lithiated
ethyldiphenylphosphine oxide with a phenylalanine-derived
aldehyde and because all four diastereoisomeric alcohols are
obtained, it is necessary to determine the relative
stereochemistry of the products. This is done using a combination
of synthesis and X-ray crystallography of
(2S*,3S*,4R*)-2-(N,N-diben
zylamino)-4-diphenylphosphinoyl-1-phenylpentan-3-ol and
(2S*,4S*)-2-(N,N-dibenzylamino)-2-d
iphenylphosphinoyl-1-phenylpentan-3-one.
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