CONVENIENT AND EFFICIENT SYNTHESES OF β-KETO ESTERS AND β-KETO AMIDES DIRECTLY FROM α-ALKYLACETYL CHLORIDES

The α-alkylacetyl chlorides were slowly treated with dried triethylamine, followed by treatment with alcohols or amines, to produce β-keto esters or β-keto amides, respectively. The process is a convenient alternative to prepare β-keto esters and β-keto amides.     

以芳樟醇为手性源的β-羟基酸的不对称合成

以芳樟醇与乙酰乙酸乙酯进行酯交换反应,合成了具有手性的乙酰乙酸芳樟酯(β-酮酯),再用其与不同的格氏试剂反应,得到不对称β-羟基酸;产物分别经手性柱分析.结果表明,手性乙酰乙酸芳樟酯与格氏试剂的反应具有不同程度的立体选择性,产物为R-或S-构型过量的β-羟基酸,ee值最高达50%.     

Rhenium-catalyzed regio- and stereoselective addition of two carbon units to terminal alkynes via carbon-carbon bond cleavage of β-keto sulfones

Treatment of β-keto sulfones with terminal alkynes gave unsaturated δ-keto sulfones in good to excellent yields under rhenium catalysis. In this reaction, the insertion of the alkynes into the nonstrained carbon-carbon single bond between the α- and β-positions of the β-keto sulfones proceeded smoothly, and (Z)-isomers were produced with high regio- and stereoselectivities.     

Efficient one-pot selective reduction of esters in β-ketoesters using LiHMDS and lithium aluminium hydride

The ester functionality in β-keto esters is selectively reduced in one-pot, first by enolization using LiHMDS and then reduced with lithium aluminium hydride. This method produces β-hydroxyl ketones from the corresponding β-keto esters in high yield.     

A mild and environmentally acceptable synthetic protocol for chemoselective α-bromination of β-keto esters and 1,3-diketones

A wide variety of unsubstituted β-keto esters can be brominated chemoselectively to the corresponding α-monobromo-β-keto esters by using a combination of vanadium pentoxide, hydrogen peroxide and ammonium bromide in a biphasic system, dichloromethane-water at 0-5 °C. In addition, α-mono substituted β-keto esters, cyclic β-keto-esters and 1,3-diketones can also be brominated selectively using the same protocol.     

Palladium-catalyzed dehydrogenative β'-functionalization of β-keto esters with indoles at room temperature

The dehydrogenative β'-functionalization of α-substituted β-keto esters with indoles proceeds with high regioselectivities (C3-selective for the indole partner and β'-selective for the β-keto ester) and good yields under mild palladium catalysis at room temperature with a variety of oxidants. Two possible mechanisms involving either late or early involvement of indole are presented.     

A new method for the synthesis of N-protected β-amino-α-keto esters from fluoroalkanesulfonylazides and α-keto esters

In the presence of a secondary amine, treatment of α-keto esters with fluoroalkanesulfonyl azides at room temperature afforded N-sulfonyl protected β-amino-α-keto esters in good to excellent yields. This reaction provided a novel, direct and convenient access to N-sulfonyl protected β-amino-α-keto esters from α-keto esters and fluoroalkanesulfonyl azides under mild conditions. However, the reaction of fluoroalkanesulfonyl azides with β-ketoester enamines afforded two products: N-fluoroalkanesulfonyl amidines and diazoacetate. The reaction mechanism is discussed.     

Manganese(III)-mediated free-radical cyclization of acitve methylene compounds,alkenes and molecular oxygen. Syntheses of sulfur- and phosphorus-containing 1,2-dioxan-3-ols

The reactions of β-keto sulfoxide, β-keto sulfones, or β-keto phosphinate with 1,1-disubstituted ethenes in the presence of manganese(III) acetate and molecular oxygen yielded 4-phenylsulfinyl-, 4-phenylsulfonyl-, or 4-phosphinoyl-1,2-dioxan-3-ols 3 in moderate-to-good yields. m-Chloroperbenzoic acid oxidation of 4-phenylsulfinyl-1,2-dioxan-3-ols gave the corresponding 4-phenylsulfonyl derivatives. The temperature dependence of the reactions was observed and the stereochemistry of the 1,2-dioxan-3-ols are discussed.     

Solvent-Free Microwave-Assisted Organic Reactions Preparation of β-Keto Esters

Microwave technique has been utilised in the preparation of β-keto esters. Two different procedures are described: transesterification of β-keto esters and ring opening of 2,2,6-trimethyl-1,3-dioxin-4-one.     

Highly enantioselective Ru-catalyzed hydrogenation of β-keto esters using electron-donating bis(trialkylphosphine) ligand-TangPhos

Highly electron-donating bis(trialkylphosphine) TangPhos and its corresponding ruthenium complexes provided high enantioselectivities for the hydrogenation of β-keto esters. Up to 99.8% and 99.5% ee have been achieved in hydrogenation of β-alkyl and β-aryl substituted β-keto esters, respectively. Asymmetric hydrogenation of ethyl 4-chloro acetoacetate in 98.2% ee is also reported.     

Enzymatic reductions for the regio- and stereoselective synthesis of hydroxy-keto esters and dihydroxy esters

Ketoreductases were utilized for the stereoselective synthesis of δ-hydroxy-β-keto esters, β-hydroxy-δ-keto esters, and β,δ-dihydroxy esters. Seven out of eight possible stereoisomers were obtained from the enzymatic reduction of the corresponding β,δ-diketo ester in high enantio- and diastereomeric excess.     

One-pot three-component reaction providing 1,5-benzodiazepine derivatives

The novel one-pot three-component reaction of aromatic aldehydes, 1,2-phenylenediamine, and β-keto esters is described. This reaction involves the γ-selective C-C bond formation of β-keto esters and produces 1,5-benzodiazepine derivatives.     

Transition-metal,organic solvent and base free α-hydroxylation of β-keto esters and β-keto amides with peroxides in water

Without employing any transition metal, organic solvent and base, a facile, economical and environmentally friendly strategy has been developed for the α-hydroxylation of β-keto esters and β-keto amides with peroxides via radical cross-coupling reaction in water under open-air conditions. This protocol allows a convenient access to various α-hydroxy-β-keto esters and α-hydroxy-β-keto amides with up to 92% yield (34 examples). Moreover, the reaction was successfully scaled up to gram quantity and mechanistic studies showed the radical pathway was involved in this hydroxylation.     

Catalytic enantioselective chlorination of cyclic β-keto esters in the presence of chiral Pd(II) complexes

The catalytic enantioselective electrophilic chlorination promoted by chiral palladium complexes is described. The treatment of β-keto esters with 2,3,4,5,6,6-hexachlorocyclohex-2,4-dienone as chlorine source under mild reaction conditions afforded the corresponding α-chlorinated β-keto esters with excellent enantioselectivities (up to 94% ee).     

Double Michael addition of dithiols to acetylenic carbonyl compounds under the influence of molecular sieve and dimethyl sulfoxide

Double Michael addition of dithiols such as 1,3-propanedithiol and 1,2-ethanedithiol to α,β-acetylenic carbonyl compounds in the presence of molecular sieve and dimethyl sulfoxide proceeds very smoothly to afford the corresponding β-keto 1,3-dithianes and β-keto 1,3-dithiolanes, respectively, in good to high yields.     

Differentiation effect of solvents on the keto-enol equilibrium of heterocyclic β-dicarbonyl compounds

The differentiation effect of a solvent on the equilibrium of five- and six-membered heterocyclic β-keto esters and β-diketones containing =O, =S, =SO, =NR, =NRHC1, and -S-C(R)₂-S-fragments and, for comparison, on the equilibrium of aliphatic and carbocyclic β-keto esters and β-diketones was studied. The differentiating effect of a solvent is explained by different kinds of solvation of the heteroatomic fragments in the ketone and enol forms of heterocyclic β-dicarbonyl compounds.     

Copper-bipyridine-catalyzed enantioselective α-amination of β-keto esters

The Cu(OTf)₂-bipyridine-catalyzed, enantioselective, direct α-amination of β-keto esters and β-diketones with diethyl azodicarboxylate (DEAD) has been studied. Exceptionally high enantioselectivities of up to 99% ee were found for 1-indanone-based β-keto esters in particular even for substrates and reagents carrying conventional ester groups such as methyl and ethyl.     

Synthesis of β-keto esters in-flow and rapid access to substituted pyrimidines

We have developed an in-flow process for the synthesis of β-keto esters via the BF(3)·OEt(2)-catalyzed formal C-H insertion of ethyl diazoacetate into aldehydes. The β-keto esters were then condensed with a range of amidines to give a variety of 2,6-substituted pyrimidin-4-ols.     

Enantioselective gem-chlorofluorination of active methylene compounds using a chiral spiro oxazoline ligand

Highly enantioselective gem-chlorofluorination of active methylene compounds was carried out by using a copper(II) complex of a chiral spiro pyridyl monooxazoline ligand. This reaction yielded α-chloro-α-fluoro-β-keto esters and α-chloro-α-fluoro-β-keto phosphonates with up to 92% ee. The resulting dihalo β-keto ester was converted into various α-fluoro-α-heteroatom-substituted carbonyl compounds via nucleophilic substitution without loss of optical purity. A fully protected β-amino acid with a gem-chlorofluoromethylene function was also synthesized.     

Organocatalytic asymmetric conjugate addition and cascade acyl transfer reaction of α-nitroketones

Organocatalytic asymmetric conjugate addition of α-nitroketones to β,γ-unsaturated α-keto esters has been developed. A pyrrolidine-based thiourea-tertiary amine was identified as the best catalyst. The reaction was found to proceed via cascade conjugate addition and acyl transfer reaction. A number of α-nitroketones and β,γ-unsaturated α-keto esters were examined in this transformation. 5-Nitro-2-acyloxypent-2-enoates were obtained in good yields (up to 99%) and enantioselectivities (up to 99% ee). The products could be hydrolyzed to provide 5-nitro-2-oxopentanoates, which are not available from the direct addition of nitromethane to β,γ-unsaturated α-keto esters.