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of catalysis. Delivery of the nucleophile by the linked guanidine re-
sults in inversion of the stereochemistry.
In summary, we have shown several new chiral guanidine
organocatalysts capable of asymmetric induction in the aza-Henry
reaction. A variety of structural modifications were examined,
revealing a unique enhancement in stereoselectivity for an ethyl-
ene-linked bisguanidine. Furthermore, the enantiomeric form of
the b-nitroamine products could be selectively reversed when a
bisguanidine was used rather than a monoguanidine. Preliminary
work shows that these catalysts also provide asymmetric induction
in other carbonyl/imine addition reactions.
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Acknowledgment
The University of Washington is acknowledged for financial
support.
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Supplementary data
Supplementary data associated with this article can be found, in
References and notes
11. See Supplementary data.
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generated in substantially lower yields and enantiomeric excesses.
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1. Some recent reviews: (a) Dalko, P. I.; Moisan, L. Angew. Chem., Int. Ed. 2004, 43,
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Chem. Soc. 2002, 124, 6798–6799. For more examples see Ref. 1..
14. Common decomposition products include the aldehyde, hemiaminal, and the
b-nitroalcohols from the Henry reaction.