Iridium-Catalyzed Allylic Substitution

Iridium-Catalyzed Asymmetric Allylic Substitution Reaction of 4-Hydroxypyran-2-one

Pyranones have raised great concerns owing to their considerable applications in a variety of sectors. However, the development of direct asymmetric allylation of 4-hydroxypyran-2-ones is still restricted. Herein, we present an effective iridium-catalyzed asymmetric functionalization technique for the synthesis of 4-hydroxypyran-2-one derivatives over direct and efficient catalytic asymmetric Friedel-Crafts-type allylation by using allyl alcohols. The allylation products could be obtained with good to high yields (up to 96%) and excellent enantioselectivities (>99% ee). Therefore, the disclosed technique provides a new asymmetric synthetic strategy to explore pyranone derivatives in depth, thus providing an interesting approach for global application and further utilization in organic synthesis and pharmaceutical chemistry.

Iridium-Catalyzed Intramolecular Asymmetric Allylation of Vinyl Benzoxazinones for the Synthesis of Chiral 4H-3,1-Benzoxazines via Kinetic Resolution

Chiral benzoxazinones and 4H-3,1-benzoxazines as important motifs are widely found in abundant pharmaceuticals and biological molecules. We herein successfully developed the first kinetic resolution (KR) process of racemic benzoxazinones through Ir-catalyzed asymmetric intramolecular allylation, furnishing a wide range of chiral benzoxazinones and 4H-3,1-benzoxazines with excellent results via outstanding KR performances (with the s factor up to 170). This protocol exhibited broad substrate scope generality and good functional group tolerance, and the chiral 4H-3,1-benzoxazine products could be readily transformed to other useful optically active heterocycles.

Development of Immobilized Carreira (Phosphoramidite, Olefin) Ligands and Application in Iridium-Catalyzed Asymmetric Allylic Amination

A family of polystyrene-supported (phosphoramidite, olefin) ligands L1-L4, based on the original design by Defieber and Carreira, has been developed and applied in iridium-catalyzed asymmetric allylic amination of unmasked allylic alcohols (27 examples, up to 99% ee). Among them, functional resins L1 and L4 exhibit important advantages such as easy preparation, ligand recyclability, and easy handling for sequential use. As a distinctive advantage, the catalytic use of the iridium complexes of L1 and L4 allows the straightforward reuse of a high percentage of the expensive iridium metal involved in the complexes, which is not achievable under homogeneous conditions with the corresponding monomeric complexes.

Iridium-Catalyzed Asymmetric Cascade Allylation/Retro-Claisen Reaction

An enantiomerically enriched 3-hydroxymethyl pentenal unit is one of the key structural cores in plenty of natural products and drug candidates with significant biological activities. However, very few synthetic methodologies for the facile construction of the related skeletons have been reported to date. Herein, an elegant iridium-catalyzed asymmetric cascade allylation/retro-Claisen reaction of readily available β-diketones with VEC was successfully developed, and a wide range of functionalized chiral 3-hydroxymethyl pentenal derivatives could be prepared in good yields with excellent enantioselectivities. Various 1,3-diketones and functionalized ketones containing different electron-withdrawing groups on the β-position were well tolerated as outstanding partners with high reactivity and excellent regio-/chemo-/enantioselectivity. The synthetic utility of product chiral 3-hydroxymethyl pentenal derivatives was well shown through gram-scale transformation, hydrogenation, cyclopropanation, hydroboration, and olefin metathesis. Moreover, this elegant protocol demonstrated synthetic applications in the concise synthesis of synthetically useful chiral building block (S)-Taniguchi lactone and the formal synthesis of natural product cytisine. A rational reaction pathway was proposed based on the experimental results and control experiments.

Iridium-Catalyzed Enantioselective Ring Opening of Alkenyl Oxiranes by Unactivated Carboxylic Acids

An iridium-catalyzed enantioselective ring-opening of alkenyl oxiranes by unactivated carboxylic acids has been developed. The reaction undergoes at ambient conditions between an in-situ-generated chiral iridium-π-allyl complex and carboxylic acids to provide rapid access to valuable alkenyl diols in high yields. The synthetic utility of this method is demonstrated by the elaboration of the products into various medium and large ring-sized compounds that are part of biologically relevant molecules.

Enantioselective and Diastereodivergent Allylation of Propargylic C-H Bonds

An iridium-catalyzed stereoselective coupling of allylic ethers and alkynes to generate 3,4-substituted 1,5-enynes is reported. Under optimized conditions, the coupling products are formed with excellent regio-, diastereo-, and enantioselectivities, and the protocol is functional group tolerant. Moreover, we report conditions that allow the reaction to proceed with complete reversal of diastereoselectivity. Mechanistic studies are consistent with an unprecedented dual role for the iridium catalyst, enabling the propargylic deprotonation of the alkyne through π-coordination, as well as the generation of a π-allyl species from the allylic ether starting material.

Chiral Amines via Enantioselective π-Allyliridium-C,O-Benzoate-Catalyzed Allylic Alkylation: Student Training via Industrial-Academic Collaboration

ConspectusCyclometalated π-allyliridium-C,O-benzoate complexes discovered in the Krische laboratory display unique amphiphilic properties, catalyzing both nucleophilic carbonyl allylation and electrophilic allylation of diverse amines as well as nitronates. Given the importance of chiral amines in FDA-approved small-molecule drugs, a collaboration with medicinal chemists at Genentech that included on-site graduate student internships was undertaken to explore and expand the scope of π-allyliridium-C,O-benzoate-catalyzed allylic amination and related processes. As described in this Account, our collective experimental studies have unlocked asymmetric allylic aminations of exceptionally broad utility and scope. Specifically, using racemic branched alkyl-substituted allylic acetate proelectrophiles, primary and secondary aliphatic or aromatic amines, including indoles, engage in highly regio- and enantioselective allylic amination. Additionally, unactivated nitronates were found to be competent nucleophilic partners for regio- and enantioselective allylic alkylation, enabling entry to β-stereogenic α-quaternary primary amines. Notably, these π-allyliridium-C,O-benzoate-catalyzed allylic substitutions, which display complete branched regioselectivity in reactions of alkyl-substituted allyl electrophiles, complement the scope of corresponding iridium phosphoramidite-catalyzed allylic aminations, which require aryl-substituted allyl electrophiles to promote high levels of branched regioselectivity. Computational, kinetic, ESI-CID-MS, and isotopic labeling studies were undertaken to understand the mechanism of these processes, including the origins of regio- and enantioselectivity. Isotopic labeling studies suggest that C-N bond formation occurs through outer-sphere addition to the π-allyl. DFT calculations corroborate C-N bond formation via outer-sphere addition and suggest that early transition states and distinct trans effects of diastereomeric chiral-at-iridium π-allyl complexes render the reaction less sensitive to steric effects, accounting for complete levels of branched regioselectivity in reactions of hindered amine and nitronate nucleophiles. Reaction progress kinetic analysis (RPKA) reveals a zero-order dependence on allyl acetate, a first-order dependence on the catalyst, and a fractional-order dependence on the amine. As corroborated by ESI-CID-MS analysis, the 0.4 kinetic order dependence on the amine may reflect the intervention of cesium-bridged amine dimers, which dissociate to form monomeric cesium amide nucleophiles. Hence, the requirement of cesium carbonate (vs lower alkali metal carbonates) in these processes may reside in cesium's capacity for Lewis acid-enhanced Brønsted acidification of the amine pronucleophile. Beyond the development of catalytic processes for the synthesis of novel chiral amines, the present research was conducted by graduate students who benefited from career development experiences associated with training in both academic and industrial laboratories.

Kinetic, ESI-CID-MS and Computational Studies of π-Allyliridium C,O-Benzoate-Catalyzed Allylic Amination: Understanding the Effect of Cesium Ion

The mechanism of π-allyliridium C,O-benzoate-catalyzed allylic amination was studied by (a) reaction progress kinetic analysis (RPKA), (b) tandem ESI-MS analysis, and (c) computational studies involving density functional theory (DFT) calculations. Reaction progress kinetic analysis (RPKA) reveals a zero-order dependence on allyl acetate, first-order dependence on catalyst and fractional-order dependence on amine. These data corroborate rapid ionization of the allylic acetate followed by turnover limiting C-N bond formation. To illuminate the origins of the 0.4 kinetic order dependence on amine, ESI-MS analyses of quaternary ammonium-labelled piperazine with multistage collision induced dissociation (CID) were conducted that corroborate intervention of cesium-bridged amine dimers that dissociate to form monomeric cesium amide nucleophiles. Computational data align with RPKA and ESI-CID-MS analyses and suggest early transition states mitigate the impact of steric factors, thus enabling formation of highly substituted C-N bonds with complete levels of branched regioselectivity. Specifically, trans-effects of the iridium complex facilitate nucleophilic attack at the more substituted allyl terminus trans to phosphorus with enantioselectivity governed by steric repulsions between the chiral bisphosphine ligand and the π-allyl of a dominant diastereomer of the stereogenic-at-metal complex. Beyond defining aspects of the mechanism of π-allyliridium C,O-benzoate-catalyzed allylic amination, these data reveal that a key feature of cesium carbonate not only lies in its enhanced basicity, but also its capacity for Lewis-acid enhanced Brønsted acidification of amines.

Regio- and Enantioselective Iridium-Catalyzed Amination of Alkyl-Substituted Allylic Acetates with Secondary Amines

Robust air-stable cyclometalated π-allyliridium C,O-benzoates modified by (S)-tol-BINAP catalyze the reaction of secondary aliphatic amines with racemic alkyl-substituted allylic acetates to furnish products of allylic amination with high levels of enantioselectivity. Complete branched regioselectivities were observed despite the formation of more highly substituted C-N bonds.

Enantio- and Diastereodivergent Synthesis of Spirocycles through Dual-Metal-Catalyzed [3+2] Annulation of 2-Vinyloxiranes with Nucleophilic Dipoles

The development of efficient and straightforward methods for obtaining all optically active isomers of structurally rigid spirocycles from readily available starting materials is of great value in drug discovery and chiral ligand development. However, the stereodivergent synthesis of spirocycles bearing multiple stereocenters remains an unsolved challenge owing to steric hindrance and ring strain. Herein, we report an enantio- and diastereodivergent synthesis of rigid spirocycles through dual-metal-catalyzed [3+2] annulation of oxy π-allyl metallic dipoles with less commonly employed nucleophilic dipoles (imino esters). A series of spiro compounds bearing a pyrroline and an olefin were easily synthesized in an enantio- and diastereodivergent manner (up to 19:1 dr, >99 % ee), which showed great promise as a new type of N-olefin ligand. Preliminary mechanistic studies were also carried out to understand the process of this bimetallic catalysis.

Iridium-catalyzed C3-selective asymmetric allylation of 7-azaindoles with secondary allylic alcohols

The development of efficient synthetic methods of 7-azaindoles has been desired due to the useful biological activities and physical properties. We report the first example of the iridium-catalyzed C3-selective asymmetric allylation of 7-azaindoles with racemic secondary allylic alcohols to give only branched allylation products in good to high yields with high enantioselectivity (up to >99.5% ee). Allylic alcohols and 7-azaindoles with a variety of functional groups including halogen and heteroaromatic groups are compatible with the reaction conditions. Furthermore, transformations of the obtained allylation products are demonstrated without a significant loss of enantiomeric excess.

Asymmetric Aminomethylative Etherification of Conjugated Dienes with Aliphatic Alcohols Facilitated by Hydrogen Bonding

The asymmetric construction of allylic C-O bonds with primary or secondary aliphatic alcohols remains a substantial challenge in Pd-catalyzed allylation chemistry. Here, we report the development of an additive-free, palladium-catalyzed asymmetric aminomethylative etherification of conjugated dienes that enables the efficient, asymmetric O-allylation of primary and secondary aliphatic alcohols as well as water. Mechanism studies revealed that the hydrogen-bonding interaction between the alcohol and the in situ introduced aminomethyl moiety is critical to facilitate the nucleophilic addition of the alcohol to the π-allylpalladium species, which opened up the possibility of using aliphatic alcohols and water as nucleophilic substrates. This reaction tolerates a broad range of functional groups and shows remarkable regioselectivities and uniformly high enantioselectivities, which provides a direct and rapid approach to optically pure allylic 1,3-amino ethers and 1,3-amino alcohols from simple starting materials.

Synergistic Ir/Cu Catalysis for Asymmetric Allylic Alkylation of Oxindoles: Enantio- and Diastereoselective Construction of Quaternary and Tertiary Stereocenters

3,3-Disubstituted oxindoles bearing quaternary and tertiary stereogenic centers are privileged structural motifs, which widely exist in pharmaceutical and natural products. Herein, a highly regio-, enantio-, and diastereoselective allylic alkylation of 3-alkyl oxindoles through synergistic iridium and copper catalysis is described, which provides a series of 3,3-disubstituted oxindole derivatives containing adjacent quaternary and tertiary stereogenic centers in excellent yields, enantiomeric excess, and diastereomeric ratio (for 30 examples, up to 97 % yield, >99 % ee, and >20 : 1 dr). This method provides exclusive branched selectivity, excellent enantio- and diastereoselectivities, and good functional compatibility. Control experiments suggested that the chiral copper catalyst is required for achieving high reactivities and diastereoselectivities under mild reaction conditions.

Synthesis of C5-Allylindoles through an Iridium-Catalyzed Asymmetric Allylic Substitution/Oxidation Reaction Sequence of N-Alkyl Indolines

Iridium/Brønsted acid cooperative catalyzed asymmetric allylic substitution reactions at the C5 position of indolines have been reported for the first time. The highly efficient protocol allows rapid access to various C5-allylated products in good to high yields (48-97%) and enantioselectivities (82% to >99% ee) with wide functional group tolerance. The transformations allow not only the formation of C5-allylindoline derivatives but also the synthesis of C5-allylindole analogues in good yields and excellent stereoselectivities via an allylation/oxidation reaction sequence.

Recent Advances in Enantioselective Pd-Catalyzed Allylic Substitution: From Design to Applications

This Review compiles the evolution, mechanistic understanding, and more recent advances in enantioselective Pd-catalyzed allylic substitution and decarboxylative and oxidative allylic substitutions. For each reaction, the catalytic data, as well as examples of their application to the synthesis of more complex molecules, are collected. Sections in which we discuss key mechanistic aspects for high selectivity and a comparison with other metals (with advantages and disadvantages) are also included. For Pd-catalyzed asymmetric allylic substitution, the catalytic data are grouped according to the type of nucleophile employed. Because of the prominent position of the use of stabilized carbon nucleophiles and heteronucleophiles, many chiral ligands have been developed. To better compare the results, they are presented grouped by ligand types. Pd-catalyzed asymmetric decarboxylative reactions are mainly promoted by PHOX or Trost ligands, which justifies organizing this section in chronological order. For asymmetric oxidative allylic substitution the results are grouped according to the type of nucleophile used.

Enantioselective Iridium-Catalyzed Allylic Alkylation of Racemic Branched Alkyl-Substituted Allylic Acetates with Malonates

The regio- and enantioselective allylic substitution of branched alkyl-substituted allylic acetates employing malonates has been achieved through a process that calls for Krische's π-allyliridium C,O-benzoate catalyst. The protocol reported herein can be applied to a diverse set of branched alkyl substrates that are generally not well tolerated in the other two types of Ir-catalyzed allylation.

Iridium-Catalyzed Diastereo- and Enantioselective [4 + 3] Cycloaddition of 4-Indolyl Allylic Alcohols with Azomethine Ylides

An unprecedented iridium-catalyzed asymmetric [4 + 3] cycloaddition of racemic 4-indolyl allylic alcohols with azomethine ylides is reported. The ability of acid promoter zinc triflate to perform multiple roles is the key factor for the success of this strategy. This method provides scalable and efficient access to biologically important azepino[3,4,5-cd] indoles in good yields with generally excellent diastereo- and enantioselectivities (up to >20:1 dr and >99% ee). Mild reaction conditions, easily accessible substrates and chiral catalyst, and broad substrate scope highlight the practicality of this methodology.

Ir-Catalyzed Asymmetric Tandem Allylation/Iso-Pictet-Spengler Cyclization Reaction for the Enantioselective Construction of Tetrahydro-γ-carbolines

Ir-catalyzed asymmetric tandem allylation/iso-Pictet-Spengler cyclization of arylidenaminomalonates with indolyl allylic methyl carbonates was successfully developed, which provided a direct and practical approach to access synthetically useful and biologically active tetrahydro-γ-carboline derivatives bearing multiple functional groups and stereogenic centers in good to high yields and excellent stereoselective control (44%-96% yields, >20:1 dr, 94% → 99% ee). A wide range of substrate generality, easily available substrates, and simple chiral catalytic system displayed great potential practicality of this efficient protocol.

Kinetic resolution of racemic allylic alcohols via iridium-catalyzed asymmetric hydrogenation: scope, synthetic applications and insight into the origin of selectivity

Asymmetric hydrogenation is one of the most commonly used tools in organic synthesis, whereas, kinetic resolution via asymmetric hydrogenation is less developed. Herein, we describe the first iridium catalyzed kinetic resolution of a wide range of trisubstituted secondary and tertiary allylic alcohols. Large selectivity factors were observed in most cases (s up to 211), providing the unreacted starting materials in good yield with high levels of enantiopurity (ee up to >99%). The utility of this method is highlighted in the enantioselective formal synthesis of some bioactive natural products including pumiliotoxin A, inthomycin A and B. DFT studies and a selectivity model concerning the origin of selectivity are presented.

Asymmetric hydrogenation is one of the most commonly used tools in organic synthesis, whereas, kinetic resolution via asymmetric hydrogenation was less developed.

Enantioselective Desymmetrization of Bisphenol Derivatives via Ir-Catalyzed Allylic Dearomatization

Spirocyclic hexadienones with multiple stereogenic centers are frequently found in natural products but remain challenging targets to synthesize. Herein, we report the enantioselective desymmetrization of bisphenol derivatives via Ir-catalyzed allylic dearomatization reactions, affording spirocyclic hexadienone derivatives with up to three contiguous stereogenic centers in good yields (up to 90%) and excellent enantioselectivity (up to 99% ee). The high efficiency of this reaction is exemplified by the short reaction time (30 min), low catalyst loading (down to 0.2 mol %), and ability to perform the reaction on a gram-scale. The total syntheses of (+)-tatanan B and (+)-tatanan C were also realized using this Ir-catalyzed allylic dearomatization reaction as a key step.

Asymmetric synthesis of γ-chiral borylalkanes via sequential reduction/hydroboration using a single copper catalyst

The synthesis of γ-chiral borylalkanes through copper-catalyzed enantioselective SN2'-reduction of γ,γ-disubstituted allylic substrates and subsequent hydroboration was reported. A copper-DTBM-Segphos catalyst produced a range of γ-chiral alkylboronates from easily accessible allylic acetate or benzoate with high enantioselectivities up to 99% ee. Furthermore, selective organic transformations of the resulting γ-chiral alkylboronates generated the corresponding γ-chiral alcohol, arene and amine compounds.

Ruthenium-Catalyzed Asymmetric Allylic Alkylation of Isatins

A new ruthenium-based catalytic system for branched-selective asymmetric allylic alkylation is disclosed and applied to the synthesis of chiral isatin derivatives. The catalyst, which is generated in situ from commercially available CpRu(MeCN)₃PF₆ and a BINOL-derived phosphoramidite, is both highly active (TON up to 180) and insensitive to air and moisture. Additionally, the N-alkylated isatins accessible using this methodology are versatile building blocks that are readily transformed into chiral analogs of achiral drug molecules.

Direct Stereoconvergent Allylation of Chiral Alkylcopper Nucleophiles with Racemic Allylic Phosphates

Copper-catalyzed stereoconvergent allylation of chiral sp³ -hybridized carbon nucleophiles with a racemic mixture of acyclic secondary allylic phosphates is reported. In the presence of a copper-catalyst complexed with chiral BenzP* ligand, tandem coupling reaction of vinyl arenes, bis(pinacolato)diboron, and racemic allylic phosphates provided β-chiral alkylboronates possessing (E)-alkenyl moiety through a direct stereoconvergent allylic coupling with concomitant generation of a C(sp³ )-stereogenic center. A range of vinyl (hetero)arenes and secondary allylic phosphates bearing 1°, 2°, 3° alkyl and phenyl α-substituents were suitable for the reaction, forming products with high enantioselectivities up to 95 % ee. Density functional theory calculations were conducted in detail to elucidate the origin of the observed regioselectivity of borylcupration and stereoconvergent (E)-olefin formation from racemic allylic phosphates.

Direct enantioselective allylic substitution of 4-hydroxycoumarin derivatives with branched allylic alcohols via iridium catalysis

An iridium catalysed direct asymmetric allylic substitution reaction of 4-hydroxycoumarin derivatives with allylic alcohols with remarkably high yields and excellent enantioselectivities was realized.

Recent advances in cobalt-catalyzed allylic functionalization

Unlike many other state-of-the-art transition-metal-catalyzed allylic substitutions, cobalt-catalyzed allylic substitution has received much less attention from synthetic chemists for a long time despite the fact that cobalt is an earth-abundant, low-cost and thus much more sustainable option as either a reagent or a catalyst in organic synthesis. Recently, there has been an upsurge in the use of cobalt catalysis in allylic functionalization reactions, including allylic substitution, nucleophilic allylation, and Heck-type allylic functionalization, to construct synthetically significant building blocks featuring a double bond available for diverse downstream synthetic manipulations. This review highlights the current development of cobalt catalysis in allylic functionalization with an in-depth discussion of the reaction scope and mechanistic insights.

Iridium-Catalyzed Asymmetric Synthesis of Functionally Rich Molecules Enabled by (Phosphoramidite,Olefin) Ligands

The catalytic, asymmetric synthesis of complex molecules has been a core focus of our research program for some time because developments in the area can have an immediate impact on the identification of novel strategies for the synthesis of value-added molecules. In concert with this central interest, we have emphasized the design of ligand scaffolds as a tactic to discover and develop novel chemistry and overcome well-recognized synthetic challenges. Based on our group's work on chiral pool-derived diolefin ligands, we designed and implemented a class of hybrid (phosphoramidite,olefin) ligands, which combines the properties of both phosphoramidite and olefin motifs to impact, fine-tune, and even override the inherent reactivity of the metal center. Specifically, we have utilized these unique modifying ligands to address several recognized limitations in the field of iridium-catalyzed, asymmetric allylic substitution. The methods we have documented typically employ branched, unprotected allylic alcohols as substrates and obviate the need for rigorous exclusion of air and moisture. Following Takeuchi's seminal report demonstrating the high aptitude of Ir(I)-phosphite catalysts for  branch-selective allylic substitution, concerted efforts from numerous research laboratories have led to a broadening of the synthetic utility of this reaction class. The first section of this Account outlines the process leading to our discovery of an unprecedented (phosphoramidite,olefin) ligand and its validation in the first iridium-catalyzed amination of branched, unprotected allylic alcohols. This section continues with our work involving heteroatom-based nucleophiles within inter- and intramolecular etherification, thioetherification and spiroketalization processes. The second section highlights the use of readily available carbon nucleophiles possessing sp, sp², and sp³ hybridization in a series of enantioselective carbon-carbon bond-forming reactions. We describe how alkylzinc, allylsilane, and several classes of organotrifluoroborate nucleophiles can be coupled enantioselectively to enable construction of several key motifs including 1,5-dienes, 1,4-dienes, and 1,4-enynes. Since the unique electronic and steric properties of this class of ligands renders the (η³-allyl)-Ir(III) intermediate highly electrophilic, even weak nucleophiles such as alkyl olefins can be used. We also show that more nucleophilic alkene motifs such as enamines and in situ generated ketene acetals smoothly participate in substitution reactions with allylic alcohols to yield valuable piperidines and γ,δ-unsaturated esters, respectively. The concept of stereodivergent dual catalysis, which synergistically combines chiral amine catalysis with iridium catalysis to furnish α-allylated aldehydes containing two independently controllable stereocenters is then discussed. This process has enabled the independent, stereoselective synthesis of all four possible product stereoisomers from a single set of starting materials, and was highlighted in the stereodivergent synthesis of Δ⁹-tetrahydrocannabinol. This Account concludes with an overview of our organometallic mechanistic studies regarding relevant intermediates within the catalytic cycle of this class of allylic substitution. These studies have allowed us to better understand the origin of the unique characteristics exhibited by this catalyst in comparison to related systems.

Ir-Catalyzed Regiocontrolled Allylic Amination of Di-/Trienyl Allylic Alcohols with Secondary Amines

An unprecedented regio-controllable allylic amination of unactivated dienyl and trienyl allylic alcohols has been developed, providing an efficient approach toward the site-selective formation of C1-, C3-, and C5-/C7-amination products from the sole substrates. Key to this protocol is the use of secondary amines as the amination reagents, as well as the presence of an iridium catalyst and scandium triflate.

Regio- and Enantioselective Preparation of Chiral Allylic Sulfones Featuring Elusive Quaternary Stereocenters

We describe here the first general asymmetric synthesis of sterically encumbered α,α-disubstituted allylic sulfones via Pd-catalyzed allylic substitution. The design and application of a new and highly efficient phosphoramidite ligand (L10) proved to be crucial, and a wide variety of challenging allylic sulfones featuring quaternary stereocenters could be obtained in good yields and with good to excellent levels of regio- and enantioselectivities under attractive process conditions. The developed methodology employs easily accessible chemical feedstock including racemic allylic precursors and sodium sulfinates. The utility of the method is further demonstrated by the synthesis of the sesquiterpene (-)-Agelasidine A.

Palladium-Catalyzed Allylic Substitution Reaction of Benzothiazolylacetamide with Allylic Alcohols in Water

An efficient tetrakis(triphenylphosphine)palladium- and Brønsted acid catalyzed allylic substitution reaction of benzothiazolylacetamide with allylic alcohols in water has been developed, and the corresponding allylated products were afforded in good to excellent (up to 99%) yields with high regioselectivities. This straightforward protocol exhibits good functional group tolerance and scalability.

Synergetic iridium and amine catalysis enables asymmetric [4+2] cycloadditions of vinyl aminoalcohols with carbonyls

Catalytic asymmetric cycloadditions via transition-metal-containing dipolar intermediates are a powerful tool for synthesizing chiral heterocycles. However, within the field of palladium catalysis, compared with the well-developed normal electron-demand cycloadditions with electrophilic dipolarophiles, a general strategy for inverse electron-demand ones with nucleophilic dipolarophiles remains elusive, due to the inherent linear selectivity in the key palladium-catalyzed intermolecular allylations. Herein, based on the switched regioselectivity of iridium-catalyzed allylations, we achieved two asymmetric [4+2] cycloadditions of vinyl aminoalcohols with aldehydes and β,γ-unsaturated ketones through synergetic iridium and amine catalysis. The activation of vinyl aminoalcohols by iridium catalysts and carbonyls by amine catalysts provide a foundation for the subsequent asymmetric [4+2] cycloadditions of the resulting iridium-containing 1,4-dipoles and (di)enamine dipolarophiles. The former provides a straightforward route to a diverse set of enantio-enriched hydroquinolines bearing chiral quaternary stereocenters, and the later represent an enantio- and diastereodivergent synthesis of chiral hydroquinolines.

Inverse electron-demand cycloadditions in palladium catalysis are inherently limited by the linear selectivity in the allylic substitution step. To overcome this issue, the authors report a synergetic iridium (branched-selective) and amine catalysis in [4+2] cycloadditions of vinyl aminoalcohols with carbonyls.

Regio- and Enantioselective Iridium-Catalyzed N-Allylation of Indoles and Related Azoles with Racemic Branched Alkyl-Substituted Allylic Acetates

Cyclometallated π-allyliridium C,O-benzoates modified with (S)-tol-BINAP, which are stable to air, water, and SiO₂ , catalyze highly enantioselective N-allylations of indoles and related azoles. This reaction complements previously reported metal-catalyzed indole allylations in that complete levels of N versus C3 and branched versus linear regioselectivity are observed.

Iridium-Catalyzed Enantioselective Allylation of Aryl Enamides and Enecarbamates

Aromatic enamide and enecarbamate as a novel type of nucleophile in the asymmetric allylation of branched, racemic allylic alcohols to give homoallylic ketones has been described. Enabled by Carreira's chiral Ir (P, olefin) complex, the reactions proceed in good yields with excellent enantioselectivities.