Unsaturated Ketoesters Research Articles

Synthesis of Bicyclo[3.2.0]heptanes by Organophotoredox Catalytic Diastereoselective Anion Radical [2+2] Photocycloadditions of Arylenones under Batch and Flow Conditions

AbstractIn this study, the anion radical [2+2] photocycloaddition of aryl‐enones was investigated under batch and flow conditions. The reaction was promoted by LiBr as a Lewis acid and catalyzed by Eosin Y under visible light irradiation. Symmetrical enones and asymmetrical unsaturated ketoesters were effectively cyclized to yield substituted bicyclo[3.2.0]heptanes in high yield and diastereoselectivity. Through the exploration of different experimental setups and reaction conditions, a precise control over the diastereoselectivity of the process was achieved, favoring the formation of either cis or trans substituted bicyclo[3.2.0]heptanes. In‐flow experiments allowed to further improve the efficiency of the methodology, leading to higher productivity and space time yields. Furthermore, DFT investigations were conducted in order to elucidate the reaction mechanism.

Creation of a Chiral All-Carbon Quaternary Center Induced by CF3 and CH3 Substituents via Cu-Catalyzed Asymmetric Conjugate Addition.

Cu-catalyzed asymmetric construction of a chiral quaternary center bearing CH3 and CF3 groups was achieved with high to excellent enantioselectivity using our originally developed ligands. The asymmetric conjugate addition of Me3Al to β-CF3-substituted enones and unsaturated ketoesters proceeded efficiently. The use of unsaturated ketoesters gives optically active furanones in high yields with high enantioselectivities. The perfluoroalkyl-substituted enone does not seem to be favorable in the present reaction.

Fluorinated Chiral Pyrans Obtained via Mechanochemical Organocatalytic Michael/oxa‐Michael Cascade

Fluorine‐containing compounds are important in medicine or crop‐protection. Herein, we show asymmetric organocatalytic Michael/oxa‐Michael cascade leading to chiral fluorinated pyrans under mechanochemical conditions. Formal oxa‐Diels‐Alder reaction between fluorine containing unsaturated keto esters and β,γ‐unsaturated ketones afforded a range of drug‐like pyran derivatives in short times and good to high yields. Ball‐milling convey the reaction in short times and high product yields, while keeping high enantiomeric purities of products. The reaction is diastereodivergent depending on the use of either monofunctional amine catalysts or bifunctional thiourea or squaramide.

Highly Diastereo- and Enantioselective Formal [4 + 2] Cyclization of Nitroalkenes and Unsaturated Ketoesters under Phase-Transfer Catalysis.

A highly diastereo- and enantioselective formal [4 + 2] cyclization of α,β-unsaturated ketoesters with nitroalkenes through a tandem asymmetric Michael addition-intramolecular Henry reaction under dihydroquinine-based phase-transfer catalysis, leading to a one-pot construction of four contiguous stereochemical centers and multiple functional groups with excellent diastereo- and enantioselectivities in high yields, has been developed. The ee values of some products were increased to ∼100% in good yields after one crystallization.

Organocatalytic Remote Asymmetric Inverse‐Electron‐Demand Oxa‐Diels‐Alder Reaction of Allyl Ketones with Isatin‐Derived Unsaturated Keto Esters

AbstractA remote cascade asymmetric inverse‐electron‐demand oxa‐Diels‐Alder reaction of allyl ketones with isatin‐derived β,γ‐unsaturated α‐keto esters has been developed in the presence of a chiral bifunctional squaramide catalyst. Taking advantage of the secondary amide activating group, a series of enantioenriched 3,4’‐pyranyl spirooxindole derivatives bearing three contiguous chiral centers were attained in high yields (84 to >99%) with excellent enantioselectivities (96–99% ee). Moreover, the gram‐scale synthesis and the construction of 1‐benzazepine scaffold by the product were also demonstrated.magnified image

Divergent synthesis of chiral cyclic azides via asymmetric cycloaddition reactions of vinyl azides

Vinyl azides, bearing conjugated azide and alkene functional groups, have been recognized as versatile building blocks in organic synthesis. In general vinyl azides act as 3-atom (CCN) synthons through the fast release of molecular nitrogen and have been extensively utilized in the construction of structurally diverse N-heterocycles. Keeping the azide moiety intact in organic transformations to synthesis chiral azides is an important but challenging task. Herein, we report an enantioselective copper(II)/BOX-catalyzed cycloaddition of vinyl azides, generating diverse chiral cyclic azides. α-Aryl substituted vinyl azides react with unsaturated keto esters through an inverse-electron-demand hetero-Diels-Alder reaction to afford chiral azido dihydropyrans with excellent enatioselectivities. In contrast, cyclohexenyl azides undergo a diastereo- and enantio-selective Diels-Alder reaction giving important azido octahydronaphthalenes with three continuous stereogenic centers. Notable features of these reactions include a very broad scope, mild reaction conditions and 100% atom economy.

One‐Pot Alkynylation of Azaaryl Aldehydes and Spontaneous Base‐Free Rearrangement into Enone Esters: an Autoinductive Mechanism

A direct synthesis of γ‐oxo‐α,β‐unsaturated esters has been developed. When heteroaromatic aldehydes are reacted with deprotonated ethyl propiolate, in the presence of Me2Zn or BuLi, the newly formed propargylic alcohol rearranged spontaneously to give the corresponding unsaturated keto ester. Isotope labeling, allenol intermediate trapping and crossover experiments provided insight into the reactive sequence and suggest an autocatalytic mechanism.

Asymmetric Michael addition between kojic acid derivatives and unsaturated ketoesters promoted by C2-symmetric organocatalysts.

An efficient sterically hindered C2-symmetric bifunctional tertiary amine-squaramide organocatalyst for the asymmetric Michael addition/hemiketalization domino reaction of kojic acid derivatives with β,γ-unsaturated α-ketoesters has been designed. Pharmacology-relevant functionalized 2,3,4,8-tetrahydropyrano[3,2-b]pyran derivatives were produced over the catalyst in as low as 1 mol% with up to 99% yield and 99% ee. The procedure is at least 30-fold scalable and the catalyst is readily reusable in the catalytic reaction via acid-base extraction. Acylation of the products with (S)- or rac-ibuprofen and with undec-10-enoic acid afforded the corresponding chiral esters containing two privileged pharmacophoric motifs.

Enantioselective NHC-catalysed redox [4+2]-hetero-Diels-Alder reactions using α-aroyloxyaldehydes and unsaturated ketoesters

N-Heterocyclic carbene (NHC)-catalysed redox [4+2]-hetero-Diels-Alder reactions of α-aroyloxyaldehydes with either β,γ-unsaturated α-ketoesters or α,β-unsaturated γ-ketoesters generates substituted syn-dihydropyranones in good yield with excellent enantioselectivity (up to >99:1 er). The product diastereoselectivity is markedly dependent upon the nature of the unsaturated enone substituent. The presence of either electron-neutral or electron-rich aryl substituents gives excellent diastereoselectivity (up to >99:5 dr), while electron-deficient aryl substituents give reduced diastereoselectivity. In these cases, the syn-dihydropyranone products are more susceptible to base-promoted epimerisation at the C(4)-position under the reaction conditions, accounting for the lower diastereoselectivity obtained.

ChemInform Abstract: A Practical Synthesis of Optically Active δ‐Nitro‐α‐ketoesters and 4‐Cyclohexyl‐proline Catalyzed by Chiral Squamides.

AbstractOrganocatalytic asymmetric Michael addition of α‐nitroesters to unsaturated ketoesters followed by decarboxylation furnishes the title compounds with good enantioselectivities.

ChemInform Abstract: Chiral Bimetallic Catalysts Derived from Chiral Metal Phosphates: Enantioselective Three‐Component Asymmetric Aza‐Diels—Alder Reactions of Cyclic Ketones.

A new type of chiral bimetallic catalyst is disclosed. These chiral bimetallic catalysts are easily formed through mixing a metal Lewis acid and a metal binaphthyl phosphate (MLA/M[P]3) in solution. 1H and 31P NMR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and X-ray crystallographic analysis reveal a bimetallic structure of the Y(Yb)III/Y[P]3 complexes with bridging binaphthyl phosphate ligands. The Lewis acidity of these chiral bimetallic catalysts is readily tuned by changing either the metal Lewis acid or the chiral metal phosphate. Through cooperative metal Lewis acid–enamine catalysis, asymmetric three-component aza-Diels–Alder reactions of 5-, 6-, and 7-membered cyclic ketones, unsaturated ketoesters, and arylamines were successfully achieved to afford fused bicyclic dihydropyridines in high yields (up to 94%) with high enantioselectivity (up to 99% enantiomeric excess) and excellent chem...

Chiral Bimetallic Catalysts Derived from Chiral Metal Phosphates: Enantioselective Three-Component Asymmetric Aza-Diels-Alder Reactions of Cyclic Ketones.

A new type of chiral bimetallic catalyst is disclosed. These chiral bimetallic catalysts are easily formed through mixing a metal Lewis acid and a metal binaphthyl phosphate (MLA/M[P]3) in solution. (1)H and (31)P NMR spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry, and X-ray crystallographic analysis reveal a bimetallic structure of the Y(Yb)(III)/Y[P]3 complexes with bridging binaphthyl phosphate ligands. The Lewis acidity of these chiral bimetallic catalysts is readily tuned by changing either the metal Lewis acid or the chiral metal phosphate. Through cooperative metal Lewis acid-enamine catalysis, asymmetric three-component aza-Diels-Alder reactions of 5-, 6-, and 7-membered cyclic ketones, unsaturated ketoesters, and arylamines were successfully achieved to afford fused bicyclic dihydropyridines in high yields (up to 94%) with high enantioselectivity (up to 99% enantiomeric excess) and excellent chemoselectivity.

ChemInform Abstract: Highly Chemo‐, Enantio‐, and Regioselective Synthesis of α,α‐Disubstituted Furanones by Cu‐Catalyzed Conjugate Addition.

AbstractAsymmetric Cu‐catalyzed conjugate addition of organoaluminum reagents to unsaturated ketoesters results in fast chemo‐, regio‐, and enantioselective synthesis of furanones bearing an α‐chiral quaternary stereocenter.

Highly chemo-, enantio-, and regioselective synthesis of α,α-disubstituted furanones by Cu-catalyzed conjugate addition.

A highly chemo-, enantio-, and regioselective synthesis of furanones bearing an α,α-disubstituted quaternary stereogenic center is reported. The Cu-catalyzed enantioselective conjugate addition of organoaluminum reagents to unsaturated ketoesters at room temperature and subsequent lactonization took place. Synthetic transformations of furanones represent facile approaches to various cyclic or acyclic compounds bearing a quaternary stereogenic center.

ChemInform Abstract: An Unusual Triphenylphosphine Oxide Catalyzed Stereoselective 1,3‐Dichlorination of Unsaturated Ketoesters.

AbstractA mechanism of the title scalable reaction is proposed.

An Unusual Triphenylphosphine Oxide Catalyzed Stereoselective 1,3‐Dichlorination of Unsaturated Ketoesters

An unusual Ph3PO-catalyzed stereoselective 1,3-dicholorination of an unsaturated ketoester has been developed. The novel activation mode involved in this cascade reaction can promote consecutively elusive transformations. The products were obtained with good yields and excellent stereoselectivities. This reaction makes important complementation to the limitations associated with the field of dichlorination.

ChemInform Abstract: Reductive Homocondensation of Benzylidene‐ and Alkylidenepyruvate Esters by a P(NMe2)3‐Mediated Tandem Reaction.

AbstractA P(III)‐mediated trimerization of unsaturated keto esters to diverse oxygenated heterocycles is reported.

ChemInform Abstract: Catalytic Asymmetric Carbon—Carbon Bond Forming Reactions Catalyzed by Tetrahydroisoquinoline (TIQ) N,N′‐Dioxide Ligands.

AbstractTetrahydroisoquinoline N,N′‐dioxide is successfully applied as a chiral ligand for the Michael addition of unsaturated ketoesters (I) to dione (II) and malonates (IV).

Highly Enantioselective Aldol Reactions between Acetaldehyde and Activated Acyclic Ketones Catalyzed by Chiral Primary Amines

Highly enantioselective cross-aldol reactions between acetaldehyde and activated acyclic ketones are reported for the first time. Various acyclic ketones, such as saturated and unsaturated keto esters, reacted with acetaldehyde in the presence of a chiral primary amine and a Brønsted acid to afford optically enriched tertiary alcohols in good yields and with excellent enantioselectivities. Trifluoromethyl ketones were tolerable under the reaction conditions, thereby affording the trifluoromethyl carbinol in good-to-excellent yields and enantioselectivities. Structural modification of the chiral amines from the same chiral source switched the stereoselectivity of the products. The utility of aldol chemistry was demonstrated in the brief synthesis of functionally enriched δ-lactones. Theoretical calculations on the transition-state structure indicated that the protonated tertiary amine could effectively activate the carbonyl group of a keto ester to promote the addition process through hydrogen-bonding interaction and, simultaneously, provide an appropriate attacking pattern for the approach of the keto ester to the enamine, which is formed from acetaldehyde and the chiral catalyst, on a particular face, resulting in high enantioselectivity.

ChemInform Abstract: Highly Diastereoselective 1,3‐Dipolar Cycloaddition via in situ Formed Ketimine Ylides.

AbstractReaction of unsaturated keto esters with glycine derivative (II) is investigated with a view to obtaining the corresponding Michael adducts.