The Design of Chiral Double Hydrogen Bonding Networks and Their Applications to Catalytic Asymmetric Carbon-Carbon and Carbon-Oxygen Bond-Forming Reactions

Abstract

This review focuses on the applications of multicenter organocatalysts, which can form chiral hydrogen bonded networks. The high tunabilities of these catalysts in terms of their active sites, chiral spacers, and tolerated reaction conditions have been used advantageously in applications to various classes of catalytic asymmetric carbon-carbon and carbon-oxygen bond forming reactions. The high stereoselectivities of these reactions are attributed to the chemoselective dual activation of both the nucleophile and electrophile reacting partners in asymmetric space. The key requirements for the cooperative effects of weak noncovalent-bonding interactions are discussed.

1 Introduction

2 General Concept for the Design of Chiral Hydrogen Bonding Networks

3 Bis-thiourea-type Homo-bifunctional Organocatalysts

3.1 Enantioselective Morita-Baylis-Hillman Reaction

4 Guanidinium-Thiourea Hetero-multifunctional Organocatalysts

4.1 Catalytic Diastereo- and Enantioselective Nitroaldol Reaction of Prochiral Aldehydes

4.2 Catalytic Diastereoselective Nitroaldol Reaction of
α-Chiral Aldehydes

4.3 Catalytic Asymmetric Nitroaldol Reaction of α-Keto Esters

4.4 Catalytic Asymmetric Nitro-Mannich-type Reaction

4.5 Catalytic Asymmetric Mannich-type Reaction with Malonates

5 Guanidinium-Urea Hetero-multifunctional Organocatalysts

5.1 Catalytic Asymmetric Epoxidation with Hydrogen Per­oxide

6 Summary

Key words

asymmetric synthesis - catalysis - guanidinium - thiourea - urea

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9

For other chiral urea and thiourea catalysts, see ref. 6 and references cited therein.

12

For other chiral guanidine and guanidinium catalysts, see ref. 10 and references cited therein.

41

In the absence of KOH, the reaction did not proceed at all. In addition, no reaction occurred after pretreatment of catalyst 2a with an excess of KOH (10 equiv to 2a). In this catalytic system, KOH might deprotonate the nitroalkane.

47

Deng’s group reported an example of a cinchona alkaloid catalyzed nitroaldol reaction of α-keto esters with nitroethane; see ref. 46g.