Lead(IV) acetate mediated cleavage of β-hydroxy ethers: enantioselective synthesis of α-acetoxy carbonyl compounds

α-Acetoxy aldehydes or α-acetoxy ketones can be efficiently synthesized by treating 2,3-epoxy primary alcohols with lead tetraacetate. The reaction, which proceeds with complete regio- and stereoselectivity facilitates the enantioselective synthesis of α-acetoxy carbonyl compounds from allyl alcohols, via Sharpless epoxidation. Cyclic β-hydroxy ethers, with an oxygenated five-, six- or seven-membered ring, are transformed into α-acetoxy ethers.     

Copper-catalyzed β-boration of α,β-unsaturated carbonyl compounds with tetrahydroxydiborane

The copper-catalyzed β-boration of α,β-unsaturated carbonyl compounds with tetrahydroxydiborane has been developed. This diboron reagent allows direct, efficient access to boronic acids and their derivatives. Primary, secondary, and tertiary α,β-unsaturated amides are converted to the corresponding β-trifluoroboratoamides in good to excellent yields. The β-boration of a variety of α,β-unsaturated esters and ketones is also reported.     

Alkylating potential of α,β-unsaturated compounds

Alkylation reactions of the nucleoside guanosine (Guo) by the α,β-unsaturated compounds (α,β-UC) acrylonitrile (AN), acrylamide (AM), acrylic acid (AA) and acrolein (AC), which can act as alkylating agents of DNA, were investigated kinetically. The following conclusions were drawn: i) The Guo alkylation mechanism by AC is different from those brought about the other α,β-UC; ii) for the first three, the following sequence of alkylating potential was found: AN > AM > AA; iii) A correlation between the chemical reactivity (alkylation rate constants) of AN, AM, and AA and their capacity to form adducts with biomarkers was found. iv) Guo alkylation reactions for AN and AM occur through Michael addition mechanisms, reversible in the first case, and irreversible in the second. The equilibrium constant for the formation of the Guo-AN adduct is K(eq) (37 °C) = 5 × 10(-4); v) The low energy barrier (≈10 kJ mol(-1)) to reverse the Guo alkylation by AN reflects the easy reversibility of this reaction and its possible correction by repair mechanisms; vi) No reaction was observed for AN, AM, and AA at pH < 8.0. In contrast, Guo alkylation by AC was observed under cellular pH conditions. The reaction rate constants for the formation of the α-OH-Guo adduct (the most genotoxic isomer), is 1.5-fold faster than that of γ-OH-Guo. vii) a correlation between the chemical reactivity of α,β-UC (alkylation rate constants) and mutagenicity was found.     

Kinetics and mechanism of oxidation of α,β-unsaturated alcohols by manganese(III) acetate in aqueous sulphuric acid medium

Summary The kinetics of oxidation of ,-unsaturated alcohols (UA's), such as prop-2-ene-1-ol, but-2-ene-1-ol and 3-phenyl-prop-2-ene-1-ol, by manganese(III) acetate in aqueous H₂SO₄ at constant ionic strength and different acidities has been studied. The reaction was found to proceed through an outer sphere mechanism. The reactions were first order with respect to [Mn^III] and fractional order in [UA]. The reaction showed first order dependence in [H⁺], and the rate decreased on addition of [Mn^II]. Added salts, such as Na₂SO₄, had a negligible effect on the rate. The data suggested that disproportionation of the Mn^III-UA complex into free radicals was the rate determining step in the presence of [Mn^II]. A mechanism consistent with the experimental data is proposed. The activation parameters have been evaluated for the temperature range 298–313 K.     

The structure of some α, β-unsaturated sulfur compounds from dipole moment data

Summary Measurements have been made of the dipole moments of the following , -unsaturated organic sulfur compounds: vinylethylsulfide (1.38 D), vinylbutylsulfide (1.40 D), vinylphenylsulfide (1.27 D), vinylethylsulfoxide (3.80 D), vinylbutylsulfoxide (3.78 D), vinylphenylsulfoxide (3.83 D), divinylsulfone (4.41 D), vinylethylsulfone (4.43 D), vinylbutylsulfone (4.45 D), 1,2-diethylsulfonylethylene, cis-(2.69 D) and trans- (1.36 D)-isomers and 1,4-dibutylsulfonylbutadiene-1,3-cis-trans-(5.19 D), cis-cis-(4.11 D) and trans-trans-(4.19 D)-isomers. Some conclusions are drawn as to the structure of the compounds investigated.     

Oxidative bisdecarboxylation of α-alkoxymalonic acids with cerium(IV)

Ceric ammonium nitrate is an excellent reagent for preparing carboxylic esters from α-alkoxymalonic acids by oxidative bisdecarboxylation.     

Traceless sulfone linker cleavage triggered by ozonolysis: solid-phase synthesis of diverse α-β-unsaturated carbonyl compounds

The highly efficient and convenient protocol to prepare diverse α,β-unsaturated aldehydes, ketones, and acids via the parallel solid-phase synthesis is developed. The key sulfone linker cleavage strategy is performed by ozonolysis to generate a carbonyl moiety followed by base-mediated polymer-bound sulfinate elimination to release our desired molecules from the resin. All α,β-unsaturated carbonyl compounds are prepared in good purities and yields without further purification.     

Divergent pathways of β,γ-unsaturated α-diazocarbonyl compounds catalyzed by dirhodium and Lewis acids catalysts separately or in combination

β,γ-Unsaturated a-diazocarbonyl compounds possess two reactive sites for electrophilic addition-one at the diazo carbon and the other at the vinylogous γ-position.Controlled by catalyst,divergent transformations are achieved starting from the same starting materials,either by Lewis acid-catalyzed addition or by dirhodium-catalyzed metal carbene reactions.In select cases two catalysts working in combination or in sequence provide a relay for cascade transformations.In this review,we summarize advances in catalyst-dependent divergent transformations of β,γ-unsaturated α-diazocarbonyl compounds and highlight the potential of this exciting research area and the many challenges that remain.     

Unexpected copper(II) catalysis: catalytic amine base promoted β-borylation of α,β-unsaturated carbonyl compounds in water

Using bis(pinacolato)diboron, catalytic amounts of Cu(II), and various amine bases in water under atmospheric conditions at rt, acyclic and cyclic α,β-unsaturated ketones and esters are β-borylated in up to 98% yield. Mechanistic investigations using UV-vis spectroscopy, (11)B NMR, and solvent kinetic isotope effect suggest that the role of the amine is not only to coordinate to Cu(II) but also to activate a nucleophilic water molecule to form the reactive sp(2)-sp(3) diboron complex.     

A new pyridine synthesis starting from α, β-unsaturated carbonyl compounds

A new and mild synthetic method of substituted pyridines from α, β-unsaturated carbonyl compounds through a sequence involing (1) 1, 4-conjugate addition of thiophenol (2) condensation with a methylene ketone (3) Pummerer rearrangement to an unsaturated 1, 5-dicarbonyl compound (4) treatment with ammonia is described.     

Some anomalies in the vibrational spectra of α, β-unsaturated ketones

Summary Some anomalies in the intensities of the bands of the C=C and C=O bonds in the vibrational spectra of , -unsaturated ketones have been explained by a difference in the sequence of the frequencies of the in-phase (_s) and out-of-phase (_as) vibrations of the multiple bonds in their cis (_s<_as) and trans (_s>_as) arrangements.     

1,4-Addition of tetraethyl fluoromethylenebisphosphonate to α,β-unsaturated compounds

Tetraethyl fluoromethylenebisphosphonate in the presence of cesium carbonate in DMF undergoes efficient 1,4-addition to Michael acceptors having terminal double bond such as α,β-unsaturated ketones, esters, sulfones, sulfoxides, and phosphonates to yield the corresponding adducts (α-alkyl-α-fluoromethylenebisphosphonates) in good to excellent yields.     

Reaction of 2-aminopyridines with α, β-unsaturated acids

The reaction of 2-amino- and 2-amino-5-halopyridines with acrylic, methacrylic, and crotonic acids forms N-(2-pyridyl)- and N-(5-halo-2-pyridyl)--alanines and the betaines 2-amino-1-(2-carboxylatoethyl)pyridinium or 3,4-dihydropyrido[1,2-a]pyrimidin-2-ones, or their homologs.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 80–85, January, 1992.     

DABCO-catalyzed regioselective cyclization reactions of β,γ-unsaturated α-ketophosphonates or β,γ-unsaturated α-ketoesters with allenic esters

Highly efficient DABCO-catalyzed [4 + 2] cycloaddition of β,γ-unsaturated α-ketophosphonates or β,γ-unsaturated α-ketoesters with allenic esters gives the corresponding highly functionalized tetrahydropyran and dihydropyran derivatives in good to excellent yields and moderate to good regioselectivities under mild conditions.     

Asymmetric hydrogenation of α- or β-acyloxy α,β-unsaturated phosphonates catalyzed by a Rh(I) complex of monodentate phosphoramidite

The Rh(I) complex of a monodentate phosphoramidite bearing a primary amine moiety (DpenPhos) has been disclosed to be highly efficient for the asymmetric hydrogenation of a variety of α- or β-acyloxy α,β-unsaturated phosphonates, providing the corresponding biologically important chiral α- or β-hydroxy phosphonic acid derivatives with excellent enantioselectivities (90->99% ee).     

A novel synthesis of α, β-unsaturated γ-hydroxy carbonyl compounds from enones with carbon homologation

The alkylation of enone with 1-chloroalkyl phenyl sulfoxide followed by treatment with thiophenolate afforded α-phenylthio-β, γ-unsaturated carbonyl compound, which was oxidized and then hydrolyzed to give α, β-unsaturated γ-hydroxy carbonyl compound in good yield.     

Diastereoselective addition of nitro compounds to α,β-unsaturated γ-butyrolactones

Herein, we report our results on the diastereoselective addition of nitro compounds to α,β-unsaturated γ-butyrolactones, which afforded the corresponding Michael adducts 9-17 in moderate to good yields and good to excellent diastereoisomeric ratio. A one-pot conversion of α,β-unsaturated γ-butyrolactones 7 and 8 to the corresponding trisubstituted keto-γ-butyrolactones 24 and 25 via a tandem Michael-Nef protocol is also described.