Nonenzymatic Kinetic Resolution of Amines in Ionic Liquids [1]

Abstract

Ionic liquids are remarkably suitable and clean media for performing nonenzymatic kinetic resolution (KR) of amines through enantioselective N-acetylation: high levels of selectivity were obtained with a large variety of amines at room temperature (up to s = 30).

kinetic resolution - amines - ionic liquids - nonenzymatic

References and Notes

<A NAME="RD31607ST-1">1</A>

Charles Mioskowski (1946-2007).

<A NAME="RD31607ST-2">2</A>

Present address: Laboratoire de Chimie Organique, CNRS, ESPCI, 10 rue Vauquelin, 75231 Paris Cedex 05, France.

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<A NAME="RD31607ST-22">22</A>

General Procedure: The racemic amine (0.24 mmol) was added to a stirred solution of (1S,2S)-2 (50 mg, 0.12 mmol) in the chosen ionic liquid at the selected temperature. The reaction mixture was stirred at the same temperature until complete conversion of the acetylating agent [reaction followed by TLC analysis (EtOAc-n-hexane, 2:8)]. Once complete conversion of the reagent was observed, H₂O and EtOAc were added and the two phases were separated. The organic phase was dried over MgSO₄ and evaporated under reduced pressure. The resulting residue was purified by flash chromatography on silica gel (EtOAc-hexane, 1:1), and the enantiomeric excess was determined by HPLC on a chiral stationary phase.

<A NAME="RD31607ST-23">23</A>

The counterion (Cl^-, NTf₂ ^-, etc.) confers the basic character to the ionic liquids.

<A NAME="RD31607ST-24">24</A>

The equilibrium could be displaced in an enantioselective fashion by the acid-free sulfonamide.