Complete Field Guide to Asymmetric BINOL-Phosphate Derived Brønsted Acid and Metal Catalysis: History and Classification by Mode of Activation; Brønsted Acidity, Hydrogen Bonding, Ion Pairing, and Metal Phosphates

Alcohols can be temporarily converted into carbonyl compounds by the metal-catalysed removal of hydrogen. The carbonyl compounds are reactive in a wider range of transformations than the precursor alcohols and can react in situ to give imines, alkenes, and α-functionalised carbonyl compounds. The metal catalyst, which had borrowed the hydrogen, then returns it to the transformed carbonyl compound, leading to an overall process in which alcohols can be converted into amines, compounds containing CC bonds and β-functionalised alcohols.

Borrowing hydrogen in the activation of alcohols

Charged intermediates and reagents are ubiquitous in organic transformations. The interaction of these ionic species with chiral neutral, anionic, or cationic small molecules has emerged as a powerful strategy for catalytic, enantioselective synthesis. This review describes developments in the burgeoning field of asymmetric ion-pairing catalysis with an emphasis on the insights that have been gleaned into the structural and mechanistic features that contribute to high asymmetric induction.

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Asymmetric ion-pairing catalysis.

The design of artificial catalysts able to compete with the catalytic proficiency of enzymes is an intense subject of research. Non-covalent interactions are thought to be involved in several properties of enzymatic catalysis, notably (i) the confinement of the substrates and the active site within a catalytic pocket, (ii) the creation of a hydrophobic pocket in water, (iii) self-replication properties and (iv) allosteric properties. The origins of the enhanced rates and high catalytic selectivities associated with these properties are still a matter of debate. Stabilisation of the transition state and favourable conformations of the active site and the product(s) are probably part of the answer. We present here artificial catalysts and biomacromolecule hybrid catalysts which constitute good models towards the development of truly competitive artificial enzymes.

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Supramolecular catalysis. Part 2: artificial enzyme mimics

Quaternary carbon stereocentres-carbon atoms to which four distinct carbon substituents are attached-are common features of molecules found in nature. However, before recent advances in chemical catalysis, there were few methods of constructing single stereoisomers of this important structural motif. Here we discuss the many catalytic enantioselective reactions developed during the past decade for the synthesis of single stereoisomers of such organic molecules. This progress now makes it possible to incorporate quaternary stereocentres selectively in many organic molecules that are useful in medicine, agriculture and potentially other areas such as flavouring, fragrances and materials.

https://escholarship.org/content/qt1vw785m6/qt1vw785m6.pdf?t=q5l4qa

Catalytic enantioselective synthesis of quaternary carbon stereocentres

Chiral 1,2,3-triazoliums have been designed, and the rational structural modification based on their unique anion-binding abilities has led to the establishment of the highly enantioselective alkylation of 3-substituted oxindoles.

Chiral 1,2,3-Triazoliums as New Cationic Organic Catalysts with Anion-Recognition Ability: Application to Asymmetric Alkylation of Oxindoles

A palladium-catalysed, highly enantio- and diastereoselective [3 + 2] cycloaddition reaction to produce densely functionalized pyrrolidine frameworks is developed by exploiting a new phosphine ligand with a chiral ammonium salt component. Rigorous control of the individual absolute stereochemistry of three contiguous stereocentres, including vicinal all-carbon quaternary stereocentres, is possible using this methodology.

Ligand-enabled multiple absolute stereocontrol in metal-catalysed cycloaddition for construction of contiguous all-carbon quaternary stereocentres

Rather than create a chiral catalyst by combining a chiral ligand with a metal, here an achiral phosphine ligand endowed with a cationic ammonium group is ion-paired with a chiral binaphtholate A palladium catalyst based on this strategy is shown to be effective for highly enantioselective allylic alkylation of α-nitrocarboxylates

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Ion-paired chiral ligands for asymmetric palladium catalysis

A series of gold(I) complexes [AuCl(trz)] were synthesized that contain 1,2,3-triazolylidene (trz) ligands with variable wingtip groups. In the presence of AgBF4, these complexes undergo ligand redistribution to yield cationic complexes [Au(trz)2]BF4 in high yields as a result of efficient carbene transfer. Identical reactivity patterns were detected for carbene gold complexes comprised of Arduengo-type IMes ligands (IMes = N,N′-dimesityl-imidazol-2-ylidene). Reaction of cationic complexes [Au(trz)2]+ with [AuCl(trz′)] afforded the heteroleptic complex [Au(trz)(trz′)]+ and [AuCl(trz)] (trz, trz′ = triazolylidene ligands with different wingtip groups). Carbene transfer occurs spontaneously, yet is markeldy rate-enhanced in the presence of Ag+. The facile carbene transfer was exploited as a catalyst activation process to form active gold species for the aldol condensation of isocyanides and aldehydes to form oxazolines. The catalytic activity is strongly dependent on the presence of Ag+ ions to initiate cat...

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Carbene transfer from triazolylidene gold complexes as a potent strategy for inducing high catalytic activity.

A highly diastereo- and enantioselective ring-opening alkylation of racemic 2,2-disubstituted aziridines with 3-substituted oxindoles is achieved under the catalysis of a chiral 1,2,3-triazolium salt. This reaction represents a hitherto unknown, catalytic stereoselective carbon–carbon bond formation through direct substitution at the tetrasubstituted chiral carbon.

Asymmetric Substitution at the Tetrasubstituted Chiral Carbon: Catalytic Ring-Opening Alkylation of Racemic 2,2-Disubstituted Aziridines with 3-Substituted Oxindoles

Kohsuke Ohmatsu

Papers

Chiral 1,2,3-Triazoliums as New Cationic Organic Catalysts with Anion-Recognition Ability: Application to Asymmetric Alkylation of Oxindoles

Ligand-enabled multiple absolute stereocontrol in metal-catalysed cycloaddition for construction of contiguous all-carbon quaternary stereocentres

Ion-paired chiral ligands for asymmetric palladium catalysis

Carbene transfer from triazolylidene gold complexes as a potent strategy for inducing high catalytic activity.

Asymmetric Substitution at the Tetrasubstituted Chiral Carbon: Catalytic Ring-Opening Alkylation of Racemic 2,2-Disubstituted Aziridines with 3-Substituted Oxindoles