Chiral Lewis Acids

Table of Contents

1. Frontmatter

2. The Future of Catalysis by Chiral Lewis Acids

   Qiang Sha, Yongming Deng, Michael P. Doyle

   Abstract

   Even with the rapidly expanding popularity of organocatalysts for organic reactions, chiral metal-based Lewis acid catalysts continue to have a uniquely important role in asymmetric reactions. Their broad applicability to cycloaddition and condensation reactions based on close encountered associations of Lewis base reactants with these chiral Lewis acid catalysts provides architecturally confined complexes that provide high stereocontrol in their chemical reactions.

3. Chiral Bimetallic Lewis Acids

   Masakatsu Shibasaki, Naoya Kumagai

   Abstract

   Here, we review the utility of chiral bimetallic (multimetallic) Lewis acidic complexes in catalytic asymmetric transformations. Bimetallic complexes are endowed with dual catalytic functions that synergistically activate multiple substrates and functionalities. This cooperative activation mode is particularly effective for activating low reactivity substrates in a highly stereoselective manner without the aid of stoichiometric activating reagents. The privileged bimetallic catalysts presented here highlight the importance of catalyst design in the development of widely applicable catalytic systems.

4. Chiral Carbophilic Gold Lewis Acid Complexes in Enantioselective Catalysis

   Marcel Brill, Steven P. Nolan

   Abstract

   Progress made over the last decade in the development of highly selective homogeneous gold catalysts for enantioselective synthesis is reviewed. Four different classes of gold complexes have been identified and their application in enantioselective catalysis discussed: (1) chiral bisphosphine digold complexes, (2) monogold complexes of chiral monodentate phosphorous ligands, (3) chiral aminocarbene gold complexes, and (4) gold complexes containing chiral phosphate counterions.

5. Brønsted Acid/Lewis Base Hybrid Complexes

   Manabu Hatano, Kazuaki Ishihara

   Abstract

   Recent progress on our Brønsted acid/Lewis base hybrid complexes in some asymmetric catalyses is reviewed. Based on the rational design of conjugated acid–base catalysts, tailor-made supramolecular catalysts can show remarkable catalytic activity and higher-ordered selectivities that cannot be realized by ready-made single-molecule catalysts. The chiral supramolecular magnesium(II) binaphtholate complexes trigger the highly enantioselective 1,4-hydrophosphinylation and 1,2-hydrophosphonylation of α,β-unsaturated carbonyl compounds, direct Mannich-type reaction, and hetero-Diels–Alder reaction. Moreover, the advanced supramolecular catalysts are prepared in situ from chiral 3,3′-disubstituted binaphthols and biphenols, arylboronic acid, and B(C₆F₅)₃, for promoting the anomalous endo-/exo-selective Diels–Alder reaction. The specific mechanism and deep insights into the possible key intermediates are discussed on the basis of rational design of chiral supramolecular Brønsted acid/Lewis base hybrid catalysts as artificial enzymes.

6. Chiral Alkaline Earth Metal Complexes in Asymmetric Catalysis

   Yasuhiro Yamashita, Tetsu Tsubogo, Shū Kobayashi

   Abstract

   Alkaline earth metal catalysis for asymmetric reactions is a hot topic from the viewpoint of green sustainable chemistry. The stable alkaline earth metals, calcium (Ca), strontium (Sr), and barium (Ba) are abundant in the Earth’s crust, and their strong Brønsted basicity and mild Lewis acidity are useful for construction of alkaline earth metal complexes as chiral catalysts. In this chapter, the development of chiral alkaline earth metal catalysts for catalytic asymmetric reactions is described. The chiral alkaline earth metal complexes are categorized into three types of complexes, types I–III, by coordination modes, and those complexes successfully promoted many types of reactions in acid–base catalysis with high enantioselectivities.

7. Chiral Lewis Acid Rare-Earth Metal Complexes in Enantioselective Catalysis

   Xiaoming Feng, Zhen Wang, Xiaohua Liu

   Abstract

   The progress made over the past two decades in asymmetric catalysis, focusing on chiral Lewis acid complexes of rare-earth metal, is reviewed. The applications of several different catalytic systems of chiral Lewis acid complexes in various asymmetric reactions have been discussed: (1) asymmetric aldol reaction, (2) asymmetric Mannich reaction, (3) asymmetric Michael reaction, (4) asymmetric Friedel-Crafts reaction, (5) asymmetric homologation of carbonyl compounds with α-diazoesters, (6) asymmetric ene-type reaction, (7) asymmetric cycloaddition reaction, (8) asymmetric ring-opening reaction, and (9) asymmetric miscellaneous reaction.

8. Chiral Borane-Based Lewis Acids for Metal Free Hydrogenations

   Jan Paradies

   Abstract

   The unquenched reactivity of strong Lewis acids in the presence of Lewis bases in solution, the so-called frustrated Lewis pairs (FLP), has led to the discovery of the metal-free activations, whereas the FLP-mediated hydrogen activation is the most prominent. So far, the metal-free hydrogenation is the most studied application of FLP chemistry and highly efficient methodologies for a number of unsaturated substrates have been developed. This chapter starts with a brief introduction to frustrated Lewis pair chemistry. The second part focuses on the synthetic challenges of chiral borane-derived Lewis acids for asymmetric transformations. The last part gives a state-of-the-art summary of asymmetric transformations using chiral FLPs.

9. Backmatter