Palladium-Catalyzed Asymmetric Allylic Alkylations of Colby Pro-Enolates with MBH Carbonates: Enantioselective Access to Quaternary C-F Oxindoles

Organocatalyzed Asymmetric Michael Addition of 3-Fluorooxindole to Vinylidene Bisphosphonates

Both the 3-fluorooxindole and germinal bisphosphonate structural motifs are prevalent in bioactive molecules because of their associated biological activities. We describe an approach to accessing 3,3-disubstituted 3-fluorooxindoles bearing a geminal bisphosphate fragment through a highly enantioselective Michael addition reaction between 3-fluorooxindoles and vinylidene bisphosphonates. These reactions are catalyzed by a commercially available cinchona alkaloid catalyst, have a broad substrate scope concerning 3-fluorooxindoles, and provide the corresponding addition products in a yield of up to 95% with an enantiomeric excess of up to 95%. A reasonable reaction pathway to explain the observed stereochemistry is also proposed.

Organocatalytic Asymmetric Conjugate Addition of Fluorooxindoles to Quinone Methides

Fluorooxindoles undergo asymmetric Michael addition to para-quinone methides under phase-transfer conditions with 10 mol% of a readily available cinchona alkaloid ammonium catalyst. This reaction affords sterically encumbered, multifunctional fluorinated organic compounds displaying two adjacent chirality centers with high yields, ee's and dr's.

Chiral Phosphine Ligands of COAP and SKP Switched Regiodivergent Asymmetric Allylic Alkylation of MBH Adducts

The palladium-catalyzed highly regioselective asymmetric allylic alkylation of 3'-indolyl-3-oxindole derivatives with Morita-Baylis-Hillman (MBH) carbonates was developed to facilely construct chiral 3,3'-bisindole derivatives under mild reaction conditions. The regioselectivity (α/γ) of MBH carbonates was efficiently switched in the presence of chiral oxalamide phosphine or spiroketal-based diphosphine/Pd(0) complexes as a chiral catalyst. A series of multifunctional 3,3'-bisindole derivatives with all-carbon quaternary stereogenic centers were obtained in high yields with good to excellent enantio-, diastereo-, and regioselectivity. The present process is endowed with some salient features such as broad substrate scope, N-protecting group-free, excellent stereoselectivity, as well as adjustable regioselectivity.

Pd-Catalysed asymmetric allylic alkylation of heterocycles: a user's guide

This review provides an in-depth analysis of recent advances and strategies employed in the Pd-catalysed asymmetric allylic alkylation (Pd-AAA) of nucleophilic prochiral heterocycles. The review is divided into sections each focused on a specific family of heterocycle, where optimisation data and reaction scope have been carefully analysed in order to bring forward specific reactivity and selectivity trends. The review eventually opens on how computer-based technologies could be used to predict an ideally matched catalytic system for any given substrate. This user-guide targets chemists from all horizons interested in running a Pd-AAA reaction for the preparation of highly enantioenriched heterocyclic compounds.

Asymmetric Construction of Carbon-Fluorine Quaternary Stereogenic Centers via Synergistic Pd/Cu Catalysis

We developed an asymmetric decarboxylative allylic alkylation of vinylethylene carbonates with α-fluoro pyridinyl acetates through a synergistic palladium/copper catalysis. This protocol provides chiral allylic alcohol with carbon-fluorine quaternary stereogenic centers in good yield with good enantioselectivities and excellent regioselectivities. The utility of this approach was further demonstrated via a gram-scale experiment and derivatizations of the product.

Rhodium-Catalyzed Asymmetric Synthesis of 1,2-Disubstituted Allylic Fluorides

Although there are many methods for the asymmetric synthesis of monosubstituted allylic fluorides, construction of enantioenriched 1,2-disubstituted allylic fluorides has not been reported. To address this gap, we report an enantioselective synthesis of 1,2-disubstituted allylic fluorides using chiral diene-ligated rhodium catalyst, Et3 N ⋅ 3HF as a source of fluoride, and Morita Baylis Hillman (MBH) trichloroacetimidates. Kinetic studies show that one enantiomer of racemic MBH substrate reacts faster than the other. Computational studies reveal that both syn and anti π-allyl complexes are formed upon ionization of allylic substrate, and the syn complexes are slightly energetically favorable. This is in contrast to our previous observation for formation of monosubstituted π-allyl intermediates, in which the syn π-allyl conformation is strongly preferred. In addition, the presence of an electron-withdrawing group at C2 position of racemic MBH substrate renders 1,2-disubstituted π-allyl intermediate formation endergonic and reversible. To compare, formation of monosubstituted π-allyl intermediates was exergonic and irreversible. DFT calculations and kinetic studies support a dynamic kinetic asymmetric transformation process wherein the rate of isomerization of the 1,2-disubstituted π-allylrhodium complexes is faster than that of fluoride addition onto the more reactive intermediate. The 1,2-disubstituted allylic fluorides were obtained in good yields, enantioselectivity, and branched selectivity.

Construction of Enantioenriched Quaternary C-Cl Oxindoles through Palladium-Catalyzed Asymmetric Allylic Substitution with Chloroenolates

A palladium-catalyzed asymmetric chloroenolate allylation with vinyl benzoxazinanones under mild reaction conditions has been developed, affording a series of optically active 3,3-disubstituted oxindoles exhibiting a chloro-group and a linear aryl amino side chain in good yields with up to 96% ee. Versatile functional group tolerance on the benzene ring has been demonstrated, and the utility of this method was probed by a scale-up synthesis and highlighted by product derivatizations.

Cascade Detrifluoroacetylation, C-S Bond Cleavage, and SN2' Reaction of α,α-Difluorinated Gem-Diols with MBH Esters

A new SN2' reaction type of Morita-Baylis-Hillman (MBH) ester with sulfonyl anion, generated in situ via detrifluoroacetylation as a nucleophile is developed. Experimental results and DFT calculations disclose that the reaction proceeds via C-C bond cleavage to generate a PhSO2CF2 anion, C-S bond cleavage to generate a sulfonyl anion with the release of CF2 carbene, and an SN2' reaction with the MBH ester. The reaction features operational simplicity, wide substrate scope, high yields, and excellent stereoselectivity, which represents a new reaction mode of fluorinated gem-diols and also provides an efficient way to obtain β,γ-unsaturated sulfones.

Divergent Fluorinations of Vinylcyclopropanes: Ring-Opening 1,5-Hydrofluorination and Ring-Retaining 1,2-Difluorination

Organofluorine compounds have been widely used in pharmaceutical, agrochemical, and material sciences. Reported herein are divergent fluorination reactions of vinylcyclopropanes with different electrophiles, which allow the facile synthesis of homoallylic monofluorides and vicinal-difluorides through ring-opening 1,5-hydrofluorination and ring-retaining 1,2-difluorination, respectively. Both protocols feature mild conditions, simple operations, good functional group tolerance, and generally good yields. The practicality of these reactions is demonstrated by their scalability, as well as the successful conversion of the formed homoallylic monofluorides into other complex fluorinated molecules.

Asymmetric α-Allylation of Glycinate with Switched Chemoselectivity Enabled by Customized Bifunctional Pyridoxal Catalysts

Owing to the strong nucleophilicity of the NH₂ group, free-NH₂ glycinates react with MBH acetates to usually deliver N-allylated products even in the absence of catalysts. Without protection of the NH₂ group, chiral pyridoxal catalysts bearing an amide side chain at the C3 position of the naphthyl ring switched the chemoselectivity of the glycinates from intrinsic N-allylation to α-C allylation. The reaction formed chiral multisubstituted glutamic acid esters as S_N 2'-S_N 2' products in good yields with excellent stereoselectivity (up to 86 % yield, >20 : 1 dr, 97 % ee). As compared to pyridoxal catalysts bearing an amide side arm at the C2 position, the pyridoxals in this study have a bigger catalytic cavity to enable effective activation of larger electrophiles, such as MBH acetates and related intermediates. The reaction is proposed to proceed via a cooperative bifunctional catalysis pathway, which accounts for the high level of diastereo- and enantiocontrol of the pyridoxal catalysts.

Synthesis of oxindoles bearing a stereogenic 3-fluorinated carbon center from 3-fluorooxindoles

3,3-Disubstituted oxindoles bearing a stereogenic 3-fluorinated carbon center are privileged structural motifs present in many bioactive molecules. The straightforward functionalization of 3-fluorooxindoles constitutes a powerful method for the synthesis of 3-fully substituted 3-fluorooxindoles, taking advantage of the ease of preparation of 3-fluorooxindoles with different substitution patterns and the atom efficiency of chemical reactions. In the past decade, many papers have appeared on the synthesis of 3-fully substituted 3-fluorooxindoles from 3-fluorooxindoles. Importantly, many asymmetric catalytic methods have been developed for the enantioselective synthesis of these valuable compounds. This review summarizes the achievements in this area, and overviews synthetic opportunities that still exist.

Transition-Metal-Catalyzed Monofluoroalkylation: Strategies for the Synthesis of Alkyl Fluorides by C-C Bond Formation

Alkyl fluorides modulate the conformation, lipophilicity, metabolic stability, and p K a of compounds containing aliphatic motifs and, therefore, have been valuable for medicinal chemistry. Despite significant research in organofluorine chemistry, the synthesis of alkyl fluorides, especially chiral alkyl fluorides, remains a challenge. Most commonly, alkyl fluorides are prepared by the formation of C-F bonds (fluorination), and numerous strategies for nucleophilic, electrophilic, and radical fluorination have been reported in recent years. Although strategies to access alkyl fluorides by C-C bond formation (monofluoroalkylation) are inherently convergent and complexity-generating, they have studied less than methods based on fluorination. This Review provides an overview of recent developments in the synthesis of chiral (enantioenriched or racemic) secondary and tertiary alkyl fluorides by monofluoroalkylation catalyzed by transition-metal complexes. We expect this contribution will illuminate the potential of monofluoroalkylations to simplify the synthesis of complex alkyl fluorides and suggest further research directions in this growing field.

Recommended Tests for the Self-Disproportionation of Enantiomers (SDE) to Ensure Accurate Reporting of the Stereochemical Outcome of Enantioselective Reactions

The purpose of this review is to highlight the necessity of conducting tests to gauge the magnitude of the self-disproportionation of enantiomers (SDE) phenomenon to ensure the veracity of reported enantiomeric excess (ee) values for scalemic samples obtained from enantioselective reactions, natural products isolation, etc. The SDE always occurs to some degree whenever any scalemic sample is subjected to physicochemical processes concomitant with the fractionation of the sample, thus leading to erroneous reporting of the true ee of the sample if due care is not taken to either preclude the effects of the SDE by measurement of the ee prior to the application of physicochemical processes, suppressing the SDE, or evaluating all obtained fractions of the sample. Or even avoiding fractionation altogether if possible. There is a clear necessity to conduct tests to assess the magnitude of the SDE for the processes applied to samples and the updated and improved recommendations described herein cover chromatography and processes involving gas-phase transformations such as evaporation or sublimation.

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.

Ligand-Dependent Regiodivergent Enantioselective Allylic Alkylations of α-Trifluoromethylated Ketones

The asymmetric introduction of the CF₃ unit is a powerful tool for modifying pharmacokinetic properties and slowing metabolic degradation in medicinal chemistry. A catalytic and enantioselective addition of α-CF₃ enolates allows for expeditious access to functionalized chiral building blocks with CF₃-containing stereogenicity. The computational studies reveal that the choice of ligand in a designed palladium-complex system regulates the regioselectivity and stereoselectivity of the asymmetric allylic alkyation of α-CF₃ ketones and Morita-Baylis-Hillman adducts.

Phosphine-Catalyzed Asymmetric Allylic Alkylation of Achiral MBH Carbonates with 3,3'-Bisindolines: Enantioselective Construction of Quaternary Stereogenic Centers

The asymmetric allylic alkylation (AAA) of achiral Morita-Baylis-Hillman (MBH) carbonates with 3,3'-bisindolines under the catalysis of amino-acid-derived bifunctional phosphines was accomplished. With the AAA approach introduced herein, challenging 3,3'-bisindolines bearing an all-carbon quaternary stereocenter (C3a) have been constructed in good yields with good to excellent enantioselectivties. In addition, the synthetic value of this protocol was demonstrated by the facile synthesis of the core skeleton of gliocladin C.

A Type of Structurally Adaptable Aromatic Spiroketal Based Chiral Diphosphine Ligands in Asymmetric Catalysis

ConspectusWhile spectacular successes have been achieved in homogeneous catalysis with the use of achiral diphosphine ligands featuring a wide natural bite angle, such as XantPhos, chiral diphosphines that can induce a large P-M-P bite angle in their transition metal complexes are conspicuously less explored in asymmetric catalysis, probably due to the challenges in the identification and efficient construction of a suitable chiral backbone. In the past decade, a highly efficient synthesis of chiral aromatic spiroketals and the corresponding diphosphine ligands (SKPs) has been developed in this group.Based on a one-pot catalytic tandem double asymmetric hydrogenation-spiroketalization ring-closure reaction sequence, these SKP ligands featuring an extraordinarily long P···P distance and a flexible backbone have been readily prepared in large scale. Remarkably versatile coordination modes have been found in the complexes of SKP with some catalysis-relevant transition metals, for example, Pd, Cu, Au, and Rh. Whereas SKP enforces an unusually large bite angle in [Pd(SKP)Cl₂] and [Cu(SKP)Cl] complexes (160.1° and 132.8°, respectively), it also allows for a bimetallic Au-Au interaction (3.254 Å) in the complex of [Au₂(SKP)Cl₂] or a square-planar coordination geometry for the [Rh(SKP)(cod)]SbF₆ complex. Such an adaptable nature of SKP ligands for transition metal coordination has profound consequences in homogeneous asymmetric catalysis, as demonstrated by their unique performance in several types of catalytic asymmetric reactions. One of the most exciting examples is SKP/Pd-catalyzed asymmetric allylic amination of Morita-Baylis-Hillman (MBH) adducts, in which SKP/Pd complexes demonstrated excellent control of regio- and enantioselectivities and exhibited exceptionally high efficiency (with a TON up to 4750) in the catalysis. SKP ligands have also found a diversity of successful applications in Cu-, Au-, or Rh-catalyzed asymmetric reactions, further attesting their wide utilities in asymmetric catalysis. Overall, this class of readily accessible SKP ligands featuring a chiral aromatic spiroketal skeleton have demonstrated unique adaptable structures in a variety of transition metal complexes and provided outstanding performance in some difficult asymmetric transformations. The works delineated herein would be expected to stimulate further research efforts on the application of this type of chiral ligand and to provide useful clues in the design of new chiral diphosphine ligands with adaptable bite angles for transition metal catalyzed asymmetric reactions.

Construction of unique SCF3-containing building blocks via allylic alkylation of Morita-Baylis-Hillman adducts

Lewis base-catalyzed allylic alkylation of Morita-Baylis-Hillman adducts with α-SCF3 ketones has been demonstrated. The developed strategy provides efficient access to a series of highly functionalized scaffolds featuring trifluoromethanesufinyl motif on a stereogenic carbon.

Pd/Cu-Catalyzed Enantioselective Sequential Heck/Sonogashira Coupling: Asymmetric Synthesis of Oxindoles Containing Trifluoromethylated Quaternary Stereogenic Centers

An asymmetric palladium and copper co-catalyzed Heck/Sonogashira reaction between o-iodoacrylanilides and terminal alkynes to synthesize chiral oxindoles was developed. In particular, a wide range of CF₃ -substituted o-iodoacrylanilides reacted with terminal alkynes, affording the corresponding chiral oxindoles containing trifluoromethylated quaternary stereogenic centers in high yields with excellent enantioselectivities (94-98 % ee). This asymmetric Heck/Sonogashira reaction provides a general approach to access oxindole derivatives containing quaternary stereogenic centers including CF₃ -substituted ones.

Detrifluoroacetylative in Situ Generated Cyclic Fluorinated Enolates for the Preparation of Compounds Featuring a C-F Stereogenic Center

Practical methods for the preparation of selectively fluorinated compounds are in extremely high demand in nearly every sector of the pharmaceutical and agrochemical industries. Here we provided an account of the recent methodological breakthrough dealing with detrifluoroacetylative in situ generation of cyclic fluoro-enolates and their application for the preparation of various polyfunctional compounds featuring quaternary C-F stereogenic carbon. The reactions include aldol, Mannich, Michael addition reactions, S_N2/S_N2' alkylations, and the additions to azo compounds. The detrifluoroacetylative protocol for in situ generation of cyclic fluoro-enolates is operationally simple and scalable and proceeds at ambient temperature. Generally, the stereochemical outcome, controlled by the stoichiometric chiral auxiliary of the chiral catalyst, is synthetically useful, allowing preparation of enantiomerically pure compounds of high pharmaceutical potential.

Enantioselective Mannich Reactions of 3-Fluorooxindoles with Cyclic N-Sulfamidate Aldimines

Both the 3-fluorooxindole and cyclic sulfamidate frameworks are important in medicinal chemistry owing to their associated biological activities. We report an approach accessing 3-fully substituted 3-fluorooxindoles, containing a benzo-fused sulfamidate subunit through highly enantioselective Mannich-type reactions between 3-fluorooxindoles and cyclic benzo-fused N-sulfamidate aldimines. These reactions are promoted by a commercially available cinchona alkaloid catalyst, accommodate a broad substrate scope, and deliver the desired products in a yield of up to 99% with an enantiomeric excess of up to 94%. A plausible reaction pathway is also presented.

Chemistry of detrifluoroacetylativelyin situgenerated fluoro-enolates

This review article provides a summary of the detrifluoroacetylativein situgeneration of fluorine-containing enolates and their related reactions.

Asymmetric synthesis of multifunctional aryl allyl ethers by nucleophilic catalysis

Asymmetric allylic substitution of Morita–Baylis–Hillman (MBH) carbonates with less-nucleophilic phenols mediated by nucleophilic amine catalysis was successfully developed. A variety of substituted aryl allyl ethers were afforded with moderate to high yields with excellent enantioselectivities. The chiral MBH alcohol could be easily accessed from the corresponding aryl allyl ether.

Asymmetric allylic substitution of Morita–Baylis–Hillman (MBH) carbonates with less-nucleophilic phenols mediated by nucleophilic amine catalysis was successfully developed.