Iridium-Catalyzed Regio- and Enantioselective Allylic Substitution of Trisubstituted Allylic Electrophiles

Z-Retentive Asymmetric Allylic Substitution Reactions of Aldimine Esters under Ru/Cu Dual Catalysis

Ru/Cu dual catalysis has been applied for Z-retentive asymmetric allylic substitution reactions of aldimine esters. This reaction provides an enantioselective synthesis of chiral Z-olefins in high yields (up to 91% yield) with excellent enantioselectivity (up to 98% ee) under mild conditions. The previously unreacted trisubstituted allylic electrophiles under Ir catalytic system are found to be compatible, affording the stereoretentive products in either Z- or E-form. Both linear and branched allylic electrophiles are suitable substrates with excellent reaction outcomes. Notably, Ru and Cu complexes are added in one-pot and simplifies the manipulation of this protocol and self-sorting phenomena could be observed in this Ru/Cu dual catalytic system.

Catalytic asymmetric defluorinative allylation of silyl enol ethers

The stereocontrolled installation of alkyl fragments at the alpha position of ketones is a fundamental yet unresolved transformation in organic chemistry. Herein we report a new catalytic methodology able to construct α-allyl ketones via defluorinative allylation of silyl enol ethers in a regio-, diastereo- and enantioselective manner. The protocol leverages the unique features of the fluorine atom to simultaneously act as a leaving group and to activate the fluorophilic nucleophile via a Si-F interaction. A series of spectroscopic, electroanalytic and kinetic experiments demonstrate the crucial interplay of the Si-F interaction for successful reactivity and selectivity. The generality of the transformation is demonstrated by synthesising a wide set of structurally diverse α-allylated ketones bearing two contiguous stereocenters. Remarkably, the catalytic protocol is amenable for the allylation of biologically significant natural products.

Catalytic Asymmetric Vinylogous and Bisvinylogous Propargylic Substitution

Distinct regio- and enantioselectivity control in copper-catalyzed vinylogous and bisvinylogous propargylic substitution has been accomplished by using a novel chiral N,N,P ligand. The developed method provides an efficient and selective approach to an array of highly enantioenriched alkynyl unsaturated carbonyl compounds. Salient features include excellent functional group tolerance and broad substrate scope. The synthetic utility of the developed method is further demonstrated by a gram-scale synthesis and by application to a range of transformations including enantioselective synthesis of unique challenging compounds.

Regio- and Enantioselective γ-Allylic Alkylation of In Situ-Generated Free Dienolates via Scandium/Iridium Dual Catalysis

An unprecedented asymmetric γ-allylic alkylation of free dienolates via Sc/Ir dual catalysis is reported, which affords a range of synthetically versatile γ-allylic crotonaldehydes in high efficiency with excellent chemo-, regio-, and enantioselectivities. The dienolates bearing no essential auxiliary groups were generated in situ by scandium triflate-mediated Meinwald rearrangement of vinyloxiranes atom-economically. With the assistance of computational density functional theory calculations, a Sc/Ir bimetallic catalytic cycle was proposed to illustrate the reaction mechanism.

Rhodium-Catalyzed Regio- and Enantioselective Allylic Amination of Racemic 1,2-Disubstituted Allylic Phosphates

Alkynylphosphines are rarely used as ligands in asymmetric metal catalysis. We synthesized a series of chiral bis(oxazoline)alkynylphosphine ligands and used them in Rh-catalyzed highly regio- and enantioselective allylic amination reactions of 1,2-disubstituted allylic phosphates. Chiral 1,2-disubstituted allylic amines were synthesized in up to 95% yield with >20:1 branched/linear (b/l) ratio and 99% ee from racemic 1,2-disubstituted allylic precursors. The sterically smaller linear alkynyl group on the P atom in the bis(oxazoline)alkynylphosphine ligands was the key to fit the new requirements of the introduction of bulky 2-R' groups.

New Developments of the Principle of Vinylogy as Applied to π-Extended Enolate-Type Donor Systems

The principle of vinylogy states that the electronic effects of a functional group in a molecule are possibly transmitted to a distal position through interposed conjugated multiple bonds. As an emblematic case, the nucleophilic character of a π-extended enolate-type chain system may be relayed from the legitimate α-site to the vinylogous γ, ε, ..., ω remote carbon sites along the chain, provided that suitable HOMO-raising strategies are adopted to transform the unsaturated pronucleophilic precursors into the reactive polyenolate species. On the other hand, when "unnatural" carbonyl ipso-sites are activated as nucleophiles (umpolung), vinylogation extends the nucleophilic character to "unnatural" β, δ, ... remote sites. Merging the principle of vinylogy with activation modalities and concepts such as iminium ion/enamine organocatalysis, NHC-organocatalysis, cooperative organo/metal catalysis, bifunctional organocatalysis, dicyanoalkylidene activation, and organocascade reactions represents an impressive step forward for all vinylogous transformations. This review article celebrates this evolutionary progress, by collecting, comparing, and critically describing the achievements made over the nine year period 2010-2018, in the generation of vinylogous enolate-type donor substrates and their use in chemical synthesis.

Enantioselective Direct Vinylogous Allylic Alkylation of 4-Methylquinolones under Iridium Catalysis

The first enantioselective vinylogous allylic alkylation of 4-methylquinolones has been developed. This iridium-catalyzed reaction introduces an allyl group at the γ-position of 4-methyl-2-quinolones with exclusive branched selectivity and an excellent level of enantioselectivity. This in turn allows for the enantioselective synthesis of γ-allylquinolines and related nitrogenous heterocycles. This is the first application of 4-methylquinolones in an enantioselective transformation.

Iridium-Catalyzed Asymmetric Allylic Substitution Reactions

In this review, we summarize the origin and advancements of iridium-catalyzed asymmetric allylic substitution reactions during the past two decades. Since the first report in 1997, Ir-catalyzed asymmetric allylic substitution reactions have attracted intense attention due to their exceptionally high regio- and enantioselectivities. Ir-catalyzed asymmetric allylic substitution reactions have been significantly developed in recent years in many respects, including ligand development, mechanistic understanding, substrate scope, and application in the synthesis of complex functional molecules. In this review, an explicit outline of ligands, mechanism, scope of nucleophiles, and applications is presented.

Iridium-catalyzed enantioselective direct vinylogous allylic alkylation of coumarins

The first iridium-catalyzed enantioselective vinylogous allylic alkylation of coumarins is presented. Using easily accessible linear allylic carbonates as the allylic electrophile, this reaction installs unfunctionalized allyl groups at the γ-position of 4-methylcoumarins in an exclusively branched-selective manner generally in high yields with an excellent level of enantioselectivity (up to 99 : 1 er).

Stereodivergent Allylation of Azaaryl Acetamides and Acetates by Synergistic Iridium and Copper Catalysis

We report stereodivergent allylic substitution reactions of allylic esters with prochiral enolates derived from azaaryl acetamides and acetates to form products from addition of the enolates at the most substituted carbon of an allyl moiety with two catalysts, a chiral metallacyclic iridium complex and a chiral bisphosphine-ligated copper(I) complex, which individually control the configuration of the electrophilic and nucleophilic carbon atoms, respectively. By simple permutations of enantiomers of the two catalysts, all four stereoisomers of products containing two stereogenic centers were synthesized individually with high diastereoselectivity and enantioselectivity. A variety of azaaryl acetamides and acetates bearing pyridyl, benzothiazolyl, benzoxazolyl, pyrazinyl, quinolinyl and isoquinolinyl moieties were all found to be suitable for this transformation.

Iridium-Catalyzed Aerobic α,β-Dehydrogenation of γ,δ-Unsaturated Amides and Acids: Activation of Both α- and β-C-H bonds through an Allyl-Iridium Intermediate

Direct aerobic α,β-dehydrogenation of γ,δ-unsaturated amides and acids using a simple iridium/copper relay catalysis system is described. We developed a new strategy that overcomes the challenging issue associated with the low α-acidity of amides and acids. Instead of α-C-H metalation, this reaction proceeds by β-C-H activation, which results in enhanced α-acidity. Conjugated dienamides and dienoic acids were synthesized in excellent yield with this reaction, which uses a simple reaction protocol. Mechanistic experiments suggest a catalyst resting state mechanism in which both α-C-H and β-C-H cleavage is accelerated.

Iridium-catalyzed direct asymmetric vinylogous allylic alkylation

A catalytic asymmetric vinylogous allylic alkylation of α,β-unsaturated lactones with an iridium catalyst was achieved with excellent regio- and enantioselectivity.

Enantioselective Synthesis of Acyclic α-Quaternary Carboxylic Acid Derivatives through Iridium-Catalyzed Allylic Alkylation

The first highly enantioselective iridium-catalyzed allylic alkylation that provides access to products bearing an allylic all-carbon quaternary stereogenic center has been developed. The reaction utilizes a masked acyl cyanide (MAC) reagent, which enables the one-pot preparation of α-quaternary carboxylic acids, esters, and amides with a high degree of enantioselectivity. The utility of these products is further explored through a series of diverse product transformations.

Iridium-Catalyzed Enantioselective Allylic Substitution of Aliphatic Esters with Silyl Ketene Acetals as the Ester Enolates

Enantioselective allylic substitution with enolates derived from aliphatic esters under mild conditions remains challenging. Herein we report iridium-catalyzed enantioselective allylation reactions of silyl ketene acetals, the silicon enolates of esters, to form products containing a quaternary carbon atom at the nucleophile moiety and a tertiary carbon atom at the electrophile moiety. Under relatively neutral conditions, the allylated aliphatic esters were obtained with excellent regioselectivity and enantioselectivity. These products were readily converted into primary alcohols, carboxylic acids, amides, isocyanates, and carbamates, as well as tetrahydrofuran and γ-butyrolactone derivatives, without erosion of enantiomeric purity.