Asymmetric Allylation Research Articles

Copper(I)-Catalyzed Asymmetric Allylation of Ketones with 2-Aza-1,4-Dienes.

Catalytic asymmetric allylation of ketones under proton-transfer conditions is a challenging issue due to the limited pronucleophiles and the electrophilic inertness of ketones. Herein, a copper(I)-catalyzed asymmetric allylation of ketones with 2-aza-1,4-dienes (N-allyl-1,1-diphenylmethanimines) is disclosed, which affords a series of functionalized homoallyl tertiary alcohols in high to excellent enantioselectivity. Interestingly, N-allyl-1,1-diphenylmethanimines work as synthetic equivalents of propanals. Upon the acidic workup, a formal asymmetric β-addition of propanals to ketones is achieved. An investigation on KIE effect indicates that the deprotonation of N-allyl-1,1-diphenylmethanimines is the rate-determining step, which generates nucleophilic allyl copper(I) species. Finally, the synthetic utility of the present method is demonstrated by the asymmetric synthesis of (R)-boivinianin A and (R)-gossonorol.

Copper(I)‐Catalyzed Asymmetric Allylation of Ketones with 2‐Aza‐1,4‐Dienes

AbstractCatalytic asymmetric allylation of ketones under proton‐transfer conditions is a challenging issue due to the limited pronucleophiles and the electrophilic inertness of ketones. Herein, a copper(I)‐catalyzed asymmetric allylation of ketones with 2‐aza‐1,4‐dienes (N‐allyl‐1,1‐diphenylmethanimines) is disclosed, which affords a series of functionalized homoallyl tertiary alcohols in high to excellent enantioselectivity. Interestingly, N‐allyl‐1,1‐diphenylmethanimines work as synthetic equivalents of propanals. Upon the acidic workup, a formal asymmetric β‐addition of propanals to ketones is achieved. An investigation on KIE effect indicates that the deprotonation of N‐allyl‐1,1‐diphenylmethanimines is the rate‐determining step, which generates nucleophilic allyl copper(I) species. Finally, the synthetic utility of the present method is demonstrated by the asymmetric synthesis of (R)‐boivinianin A and (R)‐gossonorol.

TADDOL-based P,S-bidentate diastereomeric ligands in asymmetric allylation and hydrogenation reactions

Diastereomeric P,S-bidentate phosphoramidite ligands with TADDOL core and (1R,2S)-1,2-diphenyl-2-(phenylthio)-ethan-1-amine residue were synthesized. These ligands provided up to 76% ee in the Pd-catalyzed alkylation of (E)-1,3-diphenylallyl acetate with dimethyl malonate, up to 70% ee in the amination of this substrate with pyrrolidine, and 89–95% ee in the Rh-catalyzed asymmetric hydro- genation of dimethyl itaconate and methyl (Z)-2-acetamido-3-arylacrylates. The different contributions of diastereomeric chiral inducers to the catalytic outcome are discussed.

Asymmetric Pd-Catalyzed Allylation of N-Functionalized Glycine Ethyl Esters

Asymmetric Pd-Catalyzed Allylation of N-Functionalized Glycine Ethyl Esters

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.

Palladium-Catalyzed Regioselective Asymmetric Chemodivergent Allylation of Oxazolones with Morita–Baylis–Hillman Adducts

Palladium-Catalyzed Regioselective Asymmetric Chemodivergent Allylation of Oxazolones with Morita–Baylis–Hillman Adducts

Quaternary Stereocenters via Catalytic Enantioconvergent Allylation of Epoxides.

The development of catalytic and enantioselective transformations for the synthesis of all-carbon quaternary stereocenters has long been recognized as a significant challenge in organic synthesis. While considerable progress has been made in asymmetric allylations, their potential to functionalize the commonly used synthon, epoxide, remains largely underexplored. Here we demonstrate the first highly regio- and enantioselective allylation of epoxides that delivers a range of quaternary stereocenters in the face of potentially problematic elimination and protonation reactions. The reaction proceeds via a radical approach under mild conditions and benefits from the use of earth-abundant titanium with a highly sophisticated salen ligand, which facilitates remarkable enantiocontrol and suppresses undesired side reactions. The resulting allylation products are multifunctional building blocks that can be elaborated chemo- and stereoselectively to a broad array of stereodefined structural motifs.

Palladium-catalyzed asymmetric allylation via directed migration of remote dienes

Palladium-catalyzed asymmetric allylation via directed migration of remote dienes

Iridium-Catalyzed Asymmetric Allylation of Indoles via Kinetic Resolution of 1-Alken-4-yn-3-ols

AbstractWe report the iridium-catalyzed asymmetric allylation of indoles via kinetic resolution of 1-alken-4-yn-3-ols to form chiral 1-alken-4-yn-3-ols and branched allylated products with high selectivity. 1-Alken-4,6-diyn-3-ol was also found to be suitable for this asymmetric allylation and gave the products in high yield and enantioselectivity. Other nucleophiles such as a malonic ester and a thiol, besides indoles, reacted to give allylated products and 1-alken-4-yn-3-ols with high enantioselectivities.

Access to Fluorinated Quaternary Stereogenic Centers via Palladium-Catalyzed Asymmetric Allylic C–H Alkylation

AbstractA Pd-catalyzed branch- and enantioselective allylic C–H alkylation reaction has been developed for the rapid assembly of fluorinated quaternary stereogenic centers from allylarenes and prochiral α-fluorinated esters. Using chiral phosphoramidite as ligand and 2,5-diphenylquinone as oxidant, the reaction proceeds smoothly under mild conditions and tolerates a broad scope of substrates, resulting in α-quaternary fluorinated ester products with high levels of yields, enantioselectivities, and regioselectivities.

Stabilized Chiral Organic Material Containing BINAP Oxide Units as a Heterogeneous Asymmetric Organocatalyst for Allylation of Aldehydes.

Condensation of BINAPO-(PhCHO)2 and 1,3,5-tris(4-aminophenyl)benzene (TAPB) results in a new imine-based chiral organic material (COM) that can be further post-functionalized through reductive transformation of imine linkers to amines. While the imine-based material does not show the necessary stability to be used as a heterogeneous catalyst, the reduced amine-linked framework can be efficiently employed in asymmetric allylation of different aromatic aldehydes. Yields and enantiomeric excesses found are comparable to those observed for the molecular BINAP oxide catalyst, but importantly, the amine-based material also permits its recyclability.

Stereoselective synthesis of S-norvaline and related amino acids through a common intermediate.

A divergent, enantioselective synthetic strategy is reported to produce the non-proteinogenic, biologically active natural amino acids norvaline, 5-hydroxy-4-oxo-L-norvaline, and ɣ-oxonorvaline. These were synthesized in good yields (45-75%) from the common starting material (S)-allylglycine obtained by asymmetric transfer allylation of glycine Schiff base using the Corey catalyst derived from cinchonidine in more than 97% enantiomeric excess.

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.

Asymmetric synthesis of a stereopentade fragment toward latrunculins.

Latrunculins are marine toxins used in cell biology to block actin polymerization. The development of new synthetic strategies and methods for their synthesis is thus important in order to improve, modulate or control this biological value. The total syntheses found in the literature all target similar disconnections, especially an aldol strategy involving a recurrent 4-acetyl-1,3-thiazolidin-2-one ketone partner. Herein, we describe an alternative disconnection and subsequent stereoselective transformations to construct a stereopentade amenable to latrunculin and analogue synthesis, starting from (+)-β-citronellene. Key stereoselective transformations involve an asymmetric Krische allylation, an aldol reaction under 1,5-anti stereocontrol, and a Tishchenko-Evans reduction accompanied by a peculiar ester transposition, allowing to install key stereogenic centers of the natural products.

Chemo- and regioselectivities of the TBAF-catalyzed C[sbnd]F bond allylation of trifluoromethylalkenes: A theoretical view

Selective CF bond activation and functionalization of readily available polyfluorinated groups is a classical and effective way to access high value-added organofluorine compounds. Insights into origin of the selectivities could provide valuable guidance to precise manipulation and so as to get desired products. In this study, the mechanism and causation of the selective mono-CF bond allylation of trifluoromethylalkenes with tetrabutylammonium fluoride (TBAF) as catalyst has been investigated by using the density functional theory (DFT) methods. It is unveiled that the SN2′-type nucleophilic substitution going through the addition-elimination mechanism is more favorable than the concerted SN2 pathway. According to the calculation results, allyl anions would kinetically identify the trifluoromethylalkene, ammonium cation (TBA+), and difluoromethylalkene in turn, which guarantees the mono-CF bond activation under the conditions of excessive nucleophiles. Furthermore, as a specific point, the regioselectivity of the reaction using asymmetric allyl anion as the nucleophile has also been studied. The Parr function calculations and non-covalent interaction analysis reveals that the more significant nucleophilicility of the benzyl carbon atom in allyl anion and the π…π interaction between the aryl substituents on the two reacting fragments leads to favor of the reaction at the benzyl site.

Carbonyl Allylation and Crotylation: Historical Perspective, Relevance to Polyketide Synthesis, and Evolution of Enantioselective Ruthenium-Catalyzed Hydrogen Auto-Transfer Processes.

The evolution of methods for carbonyl allylation and crotylation of alcohol proelectrophiles culminating in the design of iodide-bound ruthenium-JOSIPHOS catalysts is prefaced by a brief historical perspective on asymmetric carbonyl allylation and its relevance to polyketide construction. Using gaseous allene or butadiene as precursors to allyl- or crotylruthenium nucleophiles, respectively, new capabilities for carbonyl allylation and crotylation have been unlocked, including stereo- and site-selective methods for the allylation and crotylation of 1,3-diols and related polyols.

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.

Efficient and Scalable Asymmetric Total Synthesis of (−)-Emetine with Pharmaceutical Grade Quality; First Multigram Scale Synthesis

A scalable asymmetric total synthesis of (−)-emetine, a natural product alkaloid from ipecac species and one of the main active ingredients in ipecac syrup used in emetics, has been accomplished. The synthetic route featured a total of 13 steps of highly efficient chemical reactions, including catalytic asymmetric allylation and an industrial deoxygenation of an aliphatic compound, which obviated the need for any chromatographic purification. (−)-Emetine·2HCl was obtained in 12% overall yield and over 93.2% HPLC purity. The synthesis was easily scaled up to 237.1 g and should be amenable to the production of larger quantities for ongoing drug development, while the compound is currently provided as natural ipecac syrup for a clinical use.

Asymmetric Ruthenium-Catalyzed Carbonyl Allylations by Gaseous Allene via Hydrogen Auto-Transfer: 1° vs 2° Alcohol Dehydrogenation for Streamlined Polyketide Construction.

Iodide-bound ruthenium-JOSIPHOS complexes catalyze the redox-neutral C-C coupling of primary alcohols 2a-2r with the gaseous allene (propadiene) 1a to form enantiomerically enriched homoallylic alcohols 3a-3r with complete atom-efficiency. Using formic acid as reductant, aldehydes dehydro-2a and dehydro-2c participate in reductive C-C coupling with allene to deliver adducts 3a and 3c with comparable levels of asymmetric induction. Deuterium labeling studies corroborate a mechanism in which alcohol dehydrogenation triggers allene hydroruthenation to form transient allylruthenium-aldehyde pairs that participate in carbonyl addition. Notably, due to a kinetic preference for primary alcohol dehydrogenation, chemoselective C-C coupling of 1°,2°-1,3-diols occurs in the absence of protecting groups. As illustrated by the synthesis of C7-C15 of spirastrellolide B and F (7 vs 17 steps), C3-C10 of cryptocarya diacetate (3 vs 7 or 9 steps), and a fragment common to C8'-C14' of mycolactone F (1 vs 4 steps) and C22-C28 marinomycin A (1 vs 9 steps), this capability streamlines type I polyketide construction.

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.