Design of Highly Stable Iminophosphoranes as Recyclable Organocatalysts: Application to Asymmetric Chlorinations of Oxindoles

A new family of tartaric
acid derived chiral iminophosphoranes
has been developed as highly effective organocatalysts in the asymmetric
chlorinations of 3-substituted oxindoles with a high level of enantioselectivity.
Importantly, these catalysts are air- and moisture-stable. Recovery
of the catalyst after simple chromatographic separation for reuse
in the model reaction was achieved; the catalyst can be recycled six
times without loss of any enantioselectivity. Several advantages of
this catalytic process are high conversion after a very short reaction
time at ambient temperature, low catalytic loading, and scale-up to
multigram quantities with an excellent enantiomeric excess value of
>99%, which meets the enantiomeric purity required for pharmaceutical
purposes.