Methods for the synthesis of α-keto esters

Introducing an α-Keto Ester Functional Group through Pt-Catalyzed Direct C-H Acylation with Ethyl Chlorooxoacetate

Platinum-catalyzed selective C-H acylation of 2-aryloxypyridines with ethyl chlorooxoacetate provides an efficient way of introducing an α-keto ester functional group. The reaction is oxidant-free, additive-free, and, more significantly, free of any decarbonylative side reactions. The reaction tolerates a variety of substituents from strongly electron-donating to strongly electron-withdrawing groups. Double acylation is feasible for 2-phenoxypyridine and its derivatives with only one substituent at the para position. Although the reaction of 2-(2-methylphenoxy)pyridine with ethyl malonyl chloride did not produce the desired β-keto ester, the reaction with ethyl succinyl chloride proceeded smoothly to give the γ-keto ester. Ethyl chlorooxoacetate is much more reactive than ethyl succinyl chloride in this Pt-catalyzed C-H acylation reaction.

Palladium-Catalyzed β-Arylation of α-Keto Esters

A catalyst system derived from commercially available Pd₂(dba)₃ and P^tBu₃ has been applied to the coupling of α-keto ester enolates and aryl bromides. The reaction provides access to an array of β-stereogenic α-keto esters. When the air-stable ligand precursor P^tBu₃·HBF₄ is employed, the reaction can be carried out without use of a glovebox. The derived products are of broad interest given the prevalence of the α-keto acid substructure in biologically important molecules.

2-Aryl-2-nitroacetates as central precursors to aryl nitromethanes, α-ketoesters, and α-amino acids

Nitroarylacetates are useful small molecular building blocks that act as precursors to α-ketoesters and aryl nitromethanes as well as α-amino acids. Methods were developed that produce each of these compound types in good yields. Two different conditions for decarboxylation are discussed for substrates with neutral and electron-poor aryl groups versus electron-rich aryl groups. For formation of the α-ketoesters, new mild conditions for the Nef disproportionation were identified.

Asymmetric synthesis of α-keto esters via Cu(II)-catalyzed aerobic deacylation of acetoacetate alkylation products: an unusually simple synthetic equivalent to the glyoxylate anion synthon

A simple and efficient method for the preparation of β-stereogenic α-keto esters is described using a copper(II)-catalyzed aerobic deacylation of substituted acetoacetate esters. The substrates for the title process arise from catalytic, enantioselective conjugate additions and alkylation reactions of acetoacetate esters. The mild conditions do not induce racemization of the incipient enolizable α-keto ester. The reaction is tolerant of esters, certain ketones, ketals, and nitro groups and utilizes inexpensive, readily available materials.

Catalytic nucleophilic glyoxylation of aldehydes

Beta-silyloxy-alpha-keto esters are prepared through a cyanide-catalyzed benzoin-type reaction with silyl glyoxylates and aldehydes. The products undergo a dynamic kinetic resolution to provide enantioenriched orthogonally protected alcohols and can be converted to the corresponding beta-silyloxy-alpha-amino esters.

Stereoselective synthesis of a potent thrombin inhibitor by a novel P2-P3 lactone ring opening

The concise synthesis of a potent thrombin inhibitor was accomplished by a mild lactone aminolysis between an orthogonally protected bis-benzylic amine and a diastereomerically pure lactone. The lactone was synthesized by the condensation of l-proline methyl ester with an enantiomerically pure hydroxy acid, which in turn was synthesized by a highly stereoselective (>500:1 er) and productive (100,000:1, S/C) enzymatic reduction of an alpha-ketoester. In addition, a second route to the enantiomerically pure lactone was accomplished by a diastereoselective ketoamide reduction.

Dimethylzinc-mediated addition of alkenylzirconocenes to alpha-keto and alpha-imino esters

[reaction: see text] Hydrozirconation of alkynes followed by in situ transmetalation to dimethylzinc and 1,2-addition to activated ketones and N-diphenylphosphinoylimines leads to tertiary allylic alcohols and amines in high overall yield. With 8-phenylmenthol as the chiral auxiliary, si-face attack proceeds in good to excellent diastereoselectivities.

Synthetic and theoretical studies on group-transfer imidoylation of organotellurium compounds. remarkable reactivity of isonitriles in comparison with carbon monoxide in radical-mediated reactions

Imidoylation of organotellurium compounds with isonitriles has been investigated in conjunction with the radical-mediated C1 homologation reaction by using CO and isonitriles. Carbon-centered radicals generated photochemically or thermally from organotellurium compounds react with isonitriles in a group-transfer manner to give the corresponding imidoylated products. Organotellurium compounds have been found to serve as effective precursors of a wide variety of stabilized radicals, namely benzyl, alpha-alkoxy, alpha-amino, and acyl radicals, which take part in the imidoylation with high efficiency. The reactions are compatible with various functional groups, and can be carried out in various solvents including environmentally benign water. The reactivity of isonitriles has been compared with that of CO through competition experiments, and the results indicate that isonitriles are superior to CO as radical acceptors in reactions with stabilized radicals. The origin of the differences has been addressed in theoretical studies with density functional theory calculations using the B3LYP hybrid functional. The calculations suggest that both carbonylation and imidoylation proceed with low activation energies, and that there are virtually no differences in the kinetic sense. Instead, it indicates that thermodynamic effects, namely differences in the stability of the acyl and the imidoyl radicals, control the overall course of the reactions.