Tertiary Amine-Derived Ionic Liquid-Supported Squaramide as a Recyclable Organocatalyst for Noncovalent “On Water” Catalysis

Chiral
tertiary amine-derived ionic liquid-supported squaramide was synthesized
from available precursors and applied as an efficient organocatalyst
for asymmetric Michael additions of β-dicarbonyl compounds to
α-nitroolefins in the presence of water. Corresponding Michael
adducts were generated under proposed conditions in nearly quantitative
yield with high enantioselectivity (up to 99% ee). Useful precursors
to pharmaceutically important chiral β-amino acids and anticonvulsant
Pregabalin were conveniently prepared using the developed “on
water” protocol. The catalyst is readily recoverable and reusable
over 30 times without a significant decrease of catalytic reaction
activity and selectivity.