Mannich-Type Reaction Promoted by an Ionic Liquid

Abstract

The Mannich-type reaction of silyl enolates with ald­imines occurred smoothly with [emim]OTf as a solvent and without the addition of an activator to afford β-amino carbonyl compounds in excellent yields.

ionic liquids - Mannich reaction - imine - catalysis

References

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Other examples of ionic liquid-promoted carbon-carbon bond forming reactions, see:

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<A NAME="RU02905ST-13">13</A>

We have already reported that a catalytic amount of Brønsted acid promoted the Mannich-type reaction. [3]

<A NAME="RU02905ST-14">14</A>

The Mannich-type reaction of 1a and 2a did not proceed in conventional organic solvents such as Et₂O, CH₂Cl₂, CH₃CN, CH₃OH, or toluene.

<A NAME="RU02905ST-15">15</A>

Due to the fact that [emim]OTf does not dissolve in EtOAc-hexane (4:1), recycling of the ionic liquid is easier than for [bmim]OTf.

<A NAME="RU02905ST-16">16</A> For TrSbCl₆ catalyzed Mannich-type reactions, see: Mukaiyama T. Akamatsu H. Han J.-S. Chem. Lett.  1990,  889 

For recent examples of three-component Mannich-type reactions, see:

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<A NAME="RU02905ST-17C">17c</A> Manabe K. Mori Y. Kobayashi S. Tetrahedron  2001,  57:  2537 ; see also ref.3