42597-26-2

We have discovered synthetic access to β-hydroperoxy-β-peroxylactones via BF3-catalyzed cyclizations of a variety of acyclic precursors, β-ketoesters and their silyl enol ethers, alkyl enol ethers, enol acetates, and cyclic acetals, with H2O2. Strikingly, independent of the choice of starting material, these reactions converge at the same β-hydroperoxy-β-peroxylactone products, i.e., the peroxy analogues of the previously elusive cyclic Criegee intermediate of the Baeyer-Villiger reaction. Computed thermodynamic parameters for the formation of the β-hydroperoxy-β-peroxylactones from silyl enol ethers, enol acetates, and cyclic acetals confirm that the β-peroxylactones indeed correspond to a deep energy minimum that connects a variety of the interconverting oxygen-rich species at this combined potential energy surface. The target β-hydroperoxy-β-peroxylactones were synthesized from β-ketoesters, and their silyl enol ethers, alkyl enol ethers, enol acetates, and cyclic acetals were obtained in 30-96% yields. These reactions proceed under mild conditions and open synthetic access to a broad selection of β-hydroperoxy-β-peroxylactones that are formed selectively even in those cases when alternative oxidation pathways can be expected. These β-peroxylactones are stable and can be useful for further synthetic transformations.

Ethyl 2,2-disubstituted-3-oxobutanoates were biocatalytically reduced to the corresponding (S)-ethyl 3-hydroxy-2,2-disubstitutedbutanoate with the growing cells of Klebsiella pneumoniae (NBRC 3319) with excellent enantioselection. The biocatalytically derived enantiopure hydroxyl esters were then synthetically manipulated to give (S)-4-hydroxy-3,3-disubstituted pentane-2-ones. The whole process can be regarded as an indirect enantioselective enzymatic desymmetrization method for the synthesis of (S)-4-hydroxy-3,3-disubstituted pentane-2-ones.

The substrate range of the [TiCl2(TADDOLate)] (TADDOL=α,α,α′,α′-tetraaryl-1,3-dioxolane-4, 5-dimethanol)-catalyzed asymmetric α-fluorination of activated β-carbonyl compounds has been investigated. Optimal conditions for catalysis are characterized by using 5 mol-% of TiCl2(naphthalen-1- yl)-TADDOLate) as catalyst in a saturated (0.14 mol/l) MeCN solution of F-TEDA (1-(chloromethyl)-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis- [tetrafluoroborate]) at room temperature. A series of α-methylated β-keto esters (3-oxobutanoates, 3-oxopentanoates) with bulky benzyl ester groups (60-90% ee) or phenyl ester (67-88% ee) have been fluorinated readily, whereas α-acyl lactones were also readily fluorinated, but gave lower inductions (13-46% ee). Double stereochemical differentiation in β-keto esters with chiral ester groups raised the stereoselectivity to a diastereomeric ratio (dr) of up to 96.5:3.5. For the first time, β-keto S-thioesters were asymmetrically fluorinated (62-91.5% ee) and chlorinated (83% ee). Lower inductions were observed in fluorinations of 1,3-diketones (up to 40% ee) and β-keto amides (up to 59% ee). General strategies for preparing activated β-carbonyl compounds as important model substrates for asymmetric catalytic α-functionalizations are presented (>60 examples). Copyright

Novel α,α-disubstituted epoxy esters were prepared in enantiopure form by hydrolytic kinetic resolution (HKR) of the corresponding racemic mixtures using chiral salenCo(III) as catalyst. The methodology provides a convenient route to enantioenriched β,γ-epoxy esters 2a, 2c and 2d.

The efficient synthesis of 1,1-disubstituted derivatives and the construction of cyclopropane and cyclopentane ring systems via dialkylation and cycloalkylation reactions of active methylene compounds using imidazolium salts as phase transfer catalyst is described. The dialkylation and cycloalkylation reactions of active methylene compounds in the presence of readily available imidazolium salts (ionic liquids) as phase transfer catalysts were performed to afford the respective dialkylated or cycloalkylated products. This method is very efficient for the synthesis of 1,1-disubstituted derivatives and cyclopropane and cyclopentane ring systems in a facile manner.

Lithium hydroxide-mediated alkylation of 1,3-dicarbonyl compounds proves to proceed with high efficiency and selectivity.

Highly selective mono- and di-C-alkylation of 1,3-dicarbonyl compounds with different, structurally varied alkyl halides has been achieved in high yields through a simple solvent-free reaction on the surface of alumina impregnated with sodium or potassium alkoxide.

An efficient synthesis of α-(hydroxymethyl) ketones from β-keto esters has been developed, which is experimentally simple, amenable to large scale production and provides products of high purity without resort to chromatography in most cases. The method is a useful alternative and complement to condensation processes.

A number of β-dicarbonyl compounds (2,4-pentanedione, 5,5-dimethyl-1,3-cyclohexanedione, 1,3-cyclopentanedione, ethyl 3-oxobutanoate, and diethyl propanedioate) reacted with benzyl bromide in basic aqueous solutions of hexadecyltrimethylammonium bromide at room temperature.The presence of the cationic surfactant directed the reaction toward the carbon nucleophilic site, with high chemioselectivity.C-Dialkylated species were generally predominant, due to the increased lipophilicity of the monoalkylated species, with respect to the reagent.No hydrolysis of benzyl bromide was observed in the presence of the surfactant.