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Synlett 2009(3): 354-376  
DOI: 10.1055/s-0028-1087557
ACCOUNT
© Georg Thieme Verlag Stuttgart ˙ New York

The Design of Novel, Synthetically Useful (Thio)urea-Based Organocatalysts

Stephen J. Connon
Centre for Synthesis and Chemical Biology, School of Chemistry, University of Dublin, Trinity College, Dublin 2, Ireland
Fax: +353(1)6712826; e-Mail: connons@tcd.ie;
Further Information

Publication History

Received 20 August 2008
Publication Date:
06 February 2009 (online)

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Abstract

Selected recent developments in the area of (thio)urea-mediated organocatalysis from our laboratory are summarised.

1 Introduction and Background

2 Catalysis with Achiral (Thio)ureas

2.1 The Baylis-Hillman Reaction

2.2 The Corey-Chaykovsky Reaction

2.3 Organocatalytic Reduction of Ketones

2.4 Ring Opening of Epoxides

3 Catalysis with Chiral (Thio)ureas

3.1 Modified Cinchona Alkaloid Derivatives

3.1.1 Asymmetric Michael Addition

3.1.2 Asymmetric Nitroolefin Cyclopropanation

3.1.3 meso-Anhydride Desymmetrisation

3.1.4 Dynamic Kinetic Resolution of Azlactones

3.2 Friedel-Crafts-type Reactions: Axially Chiral Thioureas

4 Summary

Key words

organocatalysis - Michael additions - asymmetric synthesis - nitroalkenes - sulfonium ions

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33

See reference [²7] for details.

37

For a recent review of this topic, see reference [¹d] .

41

This hypothesis is supported by the presence of the reduced form of BNA as the only heterocyclic species observable (by ¹H NMR spectroscopy) in the reduction of benzoin by BNA (organic phase).

42

It is assumed that product inhibition is not problematic in the systems being studied. To ensure that this is the case, the stability of the product-catalyst complex should be calculated and compared with that of the corresponding catalyst-substrate complex.

70

A simple base wash, extraction, acidification and extraction sequence furnishes pure product.

80

For a recent review of iminium catalysis, see reference [¹k] .

85

For examples of the demonstrable s-cis,cis-conformational preference of(thio)ureas, see references [8] , [9] and [49] .