Γ-keto Acids Research Articles

Photocatalytic Three-Component Acylcarboxylation of Alkenes with CO2.

γ-Keto acid is a valuable chemical motif in a wide range of fields including organic, biological, and medicinal chemistry. However, its single-step synthesis is challenging because of the mismatch of the carbonyl polarity and low tolerance of carboxylic acids. Herein, we report the single-step syntheses of γ-keto acids using alkenes and CO2. Our photocatalytic system enabled the transformation of alkenes under mild conditions in high yields (up to 95%) with broad substrate generality (35 examples).

Photocatalyzed Functionalization of Alkenoic Acids in 3D-Printed Reactors.

The valorization of alkenoic acids possibly deriving from biomass (fumaric and citraconic acids) was carried out through conversion in important building blocks, such as γ‐keto acids and succinic acid derivatives. The functionalization was carried out by addition onto the C=C double bond of radicals generated under photocatalyzed conditions from suitable hydrogen donors (mainly aldehydes) and by adopting a decatungstate salt as the photocatalyst. Syntheses were performed under batch (in a glass vessel) and flow (by using 3D‐printed reactors) conditions. The design of the latter reactors allowed for an improved yield and productivity.

Nickel-Catalyzed Asymmetric Hydrogenation of γ-Keto Acids, Esters, and Amides to Chiral γ-Lactones and γ-Hydroxy Acid Derivatives.

A highly efficient asymmetric hydrogenation of a series of γ-keto acid derivatives, including γ-keto acids, esters, and amides, using a Ni-(R,R)-QuinoxP* complex as the catalyst has been developed to afford chiral γ-hydroxy acid derivatives with excellent enantioselectivities, up to 99.9% ee. This method provides not only an economical one-pot approach for the synthesis of chiral γ-lactones but also access to (S)-norfluoxetine, an inhibitor of neural serotonin reuptake and an essential intermediate for pharmaceutical synthesis.

Visible-Light Photoredox-Catalyzed Dicarbofunctionalization of Styrenes with Oxime Esters and CO2: Multicomponent Reactions toward Cyanocarboxylic Acids and γ-Keto Acids.

A photoredox-catalyzed dicarbofunctionalization of styrenes with oxime esters and CO2 has been achieved. Notably, a series of four-, five-, or six-membered cyclic ketone oximes worked well to furnish a wide range of ε-, ζ-, and η-cyanocarboxylic acids in good yields. Furthermore, a series of γ-keto acids also could be obtained by employing acyclic ketone oxime esters as the carbonyl radical precursor. It provides convergent access to diverse biologically important cyanocarboxylic and γ-keto acids.

Asymmetric cross-aldol reactions of α-keto hydrazones and α,β-unsaturated γ-keto hydrazones with trifluoromethyl ketones.

α-Keto hydrazones and α,β-unsaturated γ-keto hydrazones are suitable pro-nucleophiles for asymmetric cross-aldol reactions with trifluoromethyl ketones via aza-di(tri)enamine-type intermediates. A quinidine-derived primary amine catalyst affords tertiary trifluoromethylated alcohols in good-to-excellent yields and high enantioselectivities. Subsequent transformations of hydrazono moieties yield appealing fluorinated carboxylic acids, 1,4-dicarbonyls and γ-keto acids.

Dual Catalytic Switchable Divergent Synthesis: An Asymmetric Visible-Light Photocatalytic Approach to Fluorine-Containing γ-Keto Acid Frameworks.

Herein, we describe a novel and efficient method for constructing a series of fluorine-containing γ-keto acid derivatives through combining visible-light photoredox catalysis and chiral Lewis acid catalysis. With this dual catalytic strategy, a variety of chiral γ-keto amides containing a gem-difluoroalkyl group and a series of fluorine-containing α,β-unsaturated-γ-keto esters were successfully constructed with high stereoselectivities, respectively. A series of experiments showed that the chemoselectivity of this process was highly dependent on the fluorine reagents besides the Lewis acid catalysts. This approach facilitates rapid access to γ-keto acid derivatives, an important class of precursors for pharmaceuticals, plasticizers, and various other additives.

Nickel-Catalyzed Desymmetrizing Cross-Electrophile Coupling of Cyclic Meso-Anhydrides.

A Ni-catalyzed desymmetrizing cross-electrophile coupling of cyclic meso-anhydrides with aryl triflates has been successfully demonstrated. This is the only example using cyclic meso-anhydrides in cross-electrophile coupling reactions. A diverse array of valuable γ-keto acid building blocks can be generated under these conditions with excellent functional group tolerance and stereochemical fidelity.

Enzyme-Inspired Chiral Secondary-Phosphine-Oxide Ligand with Dual Noncovalent Interactions for Asymmetric Hydrogenation.

Inspired by the unique character of enzymes, we developed novel chiral SPO (secondary-phosphine-oxide) ligand (SPO-Wudaphos) which can enter into both ion pair and H-bond noncovalent interactions. The novel chiral SPO-Wudaphos exhibited excellent results in the asymmetric hydrogenation of α-methylene-γ-keto carboxylic acids, affording the chiral γ-keto acids with up to over 99 % ee. A series of control experiments and DFT calculations were conducted to illustrate the critical roles of both the ion pair and H-bond noncovalent interactions.

Gallium-catalyzed reductive lactonization of γ-keto acids with a hydrosilane

Gallium chloride efficiently catalyzes cyclization of γ-keto carboxylic acids in the presence of PhSiH3 to produce the corresponding γ-lactone derivatives.

Squaramide-Catalyzed Enantioselective Michael Addition of Masked Acyl Cyanides to Substituted Enones

Masked acyl cyanide (MAC) reagents are shown to be effective umpolung synthons for enantioselective Michael addition to substituted enones. The reactions are catalyzed by chiral squaramides and afford adducts in high yields (90–99%) and with excellent enantioselectivities (85–98%). The addition products are unmasked to produce dicyanohydrins that, upon treatment with a variety of nucleophiles, provide γ-keto acids, esters, and amides. The use of this umpolung synthon has enabled, in enantiomerically enriched form, the first total synthesis of the prenylated phenol (+)-fornicin C.

2-(2-Methylbenzoyl)benzoic acid: catemeric hydrogen bonding in a γ-keto acid

The crystal structure of the title compound, C15H12O3, displays catemeric aggregation involving O—H⋯O hydrogen bonds progressing from the carboxyl group of one mol­ecule to the ketone O atom of another glide-related neighbor. The mol­ecule is twisted, with the toluene 80.61 (3)° out of plane with respect to the phenyl group of the benzoic acid. The acid group makes a dihedral angle of 13.79 (14)° with the attached phenyl ring. The mol­ecules are achiral, but the space group glide planes create alternating conformational chirality in the chain units. The four hydrogen-bonding chains progress along [001] in an A—A—B—B pattern (right-to-left versus left-to-right), and are related to each other by the center of symmetry at (0.5, 0.5, 0.5) in the chosen cell. There is one close contact (2.54 Å) between a phenyl H atom and the acid carbonyl from a symmetry-related mol­ecule.

A facile synthesis of new 3,3-disubstituted phthalides of pharmacological interest

A series of new phthalides of pharmacological interest were synthesized by a protocol involving condensation of two γ-keto acids, 2-(4-isopropylbenzoyl)benzoic acid (1a) and 2-(4-isopropyl-3-nitrobenzoyl)benzoic acid (1b) with phenolic compounds in the presence of catalytic quantity of concentrated sulphuric acid. The method is simple, efficient, economical and environmentally benign as the reaction is carried out under solvent free condition attempting a green approach. Structural characterization of these newly synthesized compounds was accomplished by IR, UV, 1H NMR, 13C NMR, Mass spectral data, elemental analysis and chemical reactions. Some of the synthesized phthalides were found to exhibit antifungal and antibacterial activity against various human pathogenic bacterial and fungal strains.

Synthesis of Ring-Substituted N -Benzyl γ-Phenyl Gaba Derivatives Via Reductive Amination

GABA derivatives are important for the development of drugs for disorders of the CNS and PNS. We describe a simple synthesis of N-benzyl γ-phenyl-γ-aminobutyric acids, via the reductive amination of the corresponding γ-keto acids with benzylamines using ammonia borane. This procedure provides an efficient and economical method for the synthesis of GABA derivatives.

Brønsted Acid Catalyzed Pictet-Spengler Cyclization of Keto Acids

Dixon and co-workers report the chiral phosphoric acid 1 catalyzed reaction between tryptamines and δ- and γ-keto acids furnishing polycyclic tetrahydro-β-carbolines in good yields and high enantioselectivities. The reaction is assumed to proceed via initial condensation of amine and ketone. Under Brønsted acid catalysis the generated imine reacts further with the acid or ester function to give two diastereoisomeric N-acyl iminium ion pairs, equilibrating with the two possible enamide intermediates. The authors ­propose that only one of the diastereomeric N-acyliminium ion pairs is attacked by the nucleophilic indole to give the desired products in a dynamic kinetic asymmetric cyclization.

ChemInform Abstract: Reactions of 3,6-Dihydrazinopyridazine with γ-Keto Acids and Ethoxymethylene Compounds.

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Some new furanones : Synthesis, characterisation and antimicrobial activity

The synthesis of some new furanones starting from three γ-keto acids, β-(3,4-dimethylbenzoyl)acrylic acid, β-(2,4-dimethylbenzoyl)acrylic acid and β-(2,5-dimethylbenzoyl)acrylic acid is described. Each acid is condensed with various phenols using catalytic quantity of sulphuric acid as condensing agent to get the furanones. The structures of synthesized compounds have been elucidated by elemental analysis, spectral data and chemical reactions. Some of the synthesized compounds have been evaluated for their antimicrobial activities also.

3-Oxocyclobutanecarboxylic acid: hydrogen bonding in a small-ring γ-keto acid

The title ketocarboxylic acid, C5H6O3, is the smallest carboxy­cyclanone to have its crystal structure determined. It adopts a chiral conformation, by rotation of its carboxyl O atoms away from the plane of skeletal symmetry that passes through the carboxyl carbon and both atoms of the ketone carbonyl. The four-membered ring is non-planar, with a shallow fold of 14.3 (1)° along a line connecting the two α-carbons of the ketone group. In the crystal, the molecules are linked by centrosymmetric hydrogen-bond pairing of ordered carboxylic acid groups [O⋯O = 2.6392 (12) Å and O—H⋯O = 175.74 (15)°], yielding two different sets of dimers, related by by a 21 screw axis in c, in the cell. A C—H⋯O interaction is also present.

Synthesis of Functionalized Pyroglutamic Acids, Part 1: The Synthetic Utility of N-Acylindole and the Ugi Reaction with a Chiral Levulinic Acid

A variety of pyroglutamic acid derivatives are readily synthesized via N-acylindole intermediates obtained by the Ugi reaction. For the preparation of functionalized pyroglutamic acid derivatives, the diastereoselectivity of the Ugi 4-center 3-component condensation reaction with a chiral γ-keto acid and convertible isocyanide is described.

Lactones 29. Enzymatic resolution of racemic γ-lactones

Studies on the application of commercially available enzymes to resolution of the racemic unsaturated γ-lactones: 5-(3-methylbutylidene)-4-methyl-tetrahydrofuran-2-one (1a) and 5-(3,3-dimethylbutylidene)-4-methyl-tetrahydrofuran-2-one (2a) are presented. Lipase PS, Rhizopus niveus lipase, Rhizopus arrhizus lipase, porcine pancreas lipase and hog liver esterase transformed substrates into their respective γ-keto acids with good efficiency (50–75%). Three of them hydrolysed the studied lactones with moderate enantioselectivity. Enantiomeric excesses determined by GC for the unreacted lactones were in the range of 20–60%. Lipase PS preferentially hydrolysed the (+) enantiomers of lactones 1a and 2a whereas R. niveus lipase hydrolysed the (−) enantiomers, respectively.

Synthesis of Chiral 5‐Aryltetrahydrofuran‐2‐ones via Yeast Bioreduction of γ‐Keto Acids and Their Esters.

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