A multifunctional (noncovalent) catalyst
containing halogen-bond
donor, hydrogen-bond donor, and Lewis basic sites was developed and
applied in an enantioselective Mannich reaction between malononitrile
and diphenylphosphinoyl-protected aldimine affording products in high
yields (up to 98%) and moderate to high enantiomeric purities (ee
up to 89%). Typically, noncovalent catalysts rely on several weak
interactions to activate the substrate, with one or two of these giving
the most notable contribution to activation. In this instance, instead
of the initially proposed coactivation by halogen bonding, it was
revealed that hydrogen bonding plays a key role in determining the
enantioselectivity.
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