Stereoselective synthesis of either (E)- or (Z)-silyl enol ether from the same acyclic α,β-unsaturated ketone using cationic rhodium complex-catalyzed 1,4-hydrosilylation

The stereoselective synthesis of either (E)- or (Z)-silyl enol ether from the same acyclic α,β-unsaturated ketone is reported. Highly (Z)-selective conditions were the use of [Rh(cod)₂]BF₄/DPPE at room temperature with no solvent, whereas (E)-selective conditions were the use of [Rh(cod)₂]BF₄/P(1-Nap)₃ (1-Nap = 1-naphthyl) under refluxing dichloromethane.     

Synthetic studies of spiroketal enol ethers: an unexpected oxidation by Martin’s sulfurane

In an attempt to synthesize a spiroketal enol ether natural product, we found that treatment of alcohol 5 with Martin’s sulfurane did not give the anticipated olefin, but instead afforded ketone 15 through an unprecedented oxidation.     

Rh-catalyzed novel α-fluoroalkylation of α,β-unsaturated ketones and its mechanism

Treatment of α,β-unsaturated ketones and fluoroalkyl halides with Et₂Zn in the presence of RhCl(PPh₃)₃ gave novel reductive fluoroalkylation products at the α-position of α,β-unsaturated ketones in moderate to good yields. The rhodium hydride complex derived from Et₂Zn and Rh catalyst seems to have played an important role in this reaction.     

Iodine-catalyzed efficient conjugate addition of pyrroles to α,β-unsaturated ketones

Iodine was used as a catalyst for the conjugate addition of pyrroles to α,β-unsaturated ketones at room temperature. Mono- and dialkylated products were obtained by using equimolar amounts of the reactants. However, the use of excess enones afforded only dialkylated products.     

Amino-acid-mediated epoxidation of α,β-unsaturated ketones by hydrogen peroxide in aqueous media

Amino acids, such as arginine and lysine, can be used as an efficient catalyst in the epoxidation of α,β-unsaturated ketones with aqueous hydrogen peroxide. Up to >99% conversion was obtained in the reaction toward 11 α,β-unsaturated ketones.     

Palladium catalyzed mild reduction of α,β-unsaturated compounds by triethylsilane

The palladium(II) chloride/triethylsilane system has been successfully applied for the selective hydrogenation of the carbon-carbon double bond of α,β-unsaturated ketones to yield the corresponding saturated carbonyl compounds. The reaction takes place under mild conditions and affords high yields.     

A novel method for the synthesis of 3-fluoro-4-aryl-2-pyridone via unprecedented denitration

A simple and novel method to the synthesis of 3-fluoro-4-aryl-2-pyridone from a Michael-adduct of fluoronitroacetate and α,β-unsaturated ketone is reported. With (NH₄)₂CO₃ as the N-source and TsOH as the promoted acid, a series of fluorinated-pyridones was obtained with moderate to good yields.     

Hydrogenation of olefins using Hantzsch ester catalyzed by palladium on carbon

Hantzsch 1,4-dihydropyridine (HEH), a well-known model compound of coenzyme NAD(P)H was found as an efficient reducing agent in hydrogenation of unactivated olefins catalyzed by Pd/C. α,β-Unsaturated ketones also underwent hydrogenation, affording the corresponding saturated ketones selectively.     

Preparation of polymer incarcerated gold nanocluster catalysts (PI-Au) and their application to aerobic oxidation reactions of boronic acids,alcohols, and silyl enol ethers

Heterogeneous gold nanocluster catalysts immobilized by the method known as polymer incarceration were prepared. Polystyrene-derived polymers with epoxide and alcohol moieties, which could be cross-linked under heating conditions, were employed as supports for their preparation. Cationic gold salts were reduced in a solution of NaBH₄ and the polymers. Poor solvents for the polymers were added, and the polymers were precipitated and encapsulated gold nanoclusters with weak but multiple interactions between a gold nanocluster surface and the π electrons of benzene rings. The polymer capsules were heated under neat conditions to afford heterogeneous gold nanocluster catalysts; namely, polymer-incarcerated gold nanoclusters. The catalysts thus prepared could be applied to the aerobic oxidation of phenyl boronic acids, alcohols, and silyl enol ethers. We found that the choice of polymers, good and poor solvents for the polymers, metal loadings, heating conditions for cross-linking, and final activation were all crucial for obtaining high-activity catalysts.     

An exceptional palladium-catalyzed alkenylation of silyl enol ether in the absence of a fluoride additive

An exceptional intramolecular palladium-catalyzed alkenylation of silyl enol ether in the absence of a fluoride additive was developed, and this reaction led to the construction of bicyclo[3.3.1]nonane ring system in reasonable yield. In this type of reactions, trialkylamines were employed as additives instead of previously indispensable fluoride additives.     

An efficient heterogeneous catalytic system for chemoselective hydrogenation of unsaturated ketones in aqueous medium

A highly chemoselective and green heterogeneous catalytic system of immobilized Ru(II)–phenanthroline complexes on amino functionalised MCM-41 material for the chemoselective hydrogenation of unsaturated ketones to unsaturated alcohols is demonstrated using water as a solvent. The XRD and FTIR spectra show the highly ordered hexagonal nature of the MCM-41, even after encapsulation of the ruthenium complex. The complex retains its configuration after anchoring, as was confirmed by FTIR and UV–Vis analysis. The detailed reaction parametric effect was studied for the hydrogenation of 3-methylpent-3-en-2-one to achieve complete conversion up to >99% chemoselectivity of 3-methylpent-3-en-2-ol. The anchored heterogeneous catalysts were recycled effectively and reused five times with marginal changes in activity and selectivity. The use of water as a solvent not only afforded high activity for the hydrogenation reaction compared to organic solvents, but also afforded a green process.     

One-pot synthesis of 1,5-diketones catalyzed by barium isopropoxide

A tandem cross-coupling reaction of aryl methyl ketones with aromatic aldehydes has been accomplished employing barium isopropoxide as a catalyst, in which barium enolates are generated and then three consecutive reactions (aldol reaction/β-elimination/conjugate addition) occur; this one-pot procedure is a convenient method to obtain symmetrical 1,5-diketones in good yields. In some cases, addition of iso-propanol is effective in improving the chemical yield.     

A simple borohydride-based method for selective 1,4-conjugate reduction of α,β-unsaturated carbonyl compounds

Sodium borohydride is used in combination with a heterogeneous palladium catalyst and acetic acid to selectively reduce the carbon-carbon double bonds of various α,β-unsaturated ketones and related compounds. This simple method is most selective when non-polar solvents such as toluene are used. We observed nearly complete conversion and high selectivities using moderate catalyst loadings. The reactions were typically complete in less than 2 h.     

Palladium-bipyridine catalyzed conjugate addition of arylboronic acids to α,β-unsaturated carbonyl compounds in aqueous media

Palladium/bipyridine catalyzed conjugate addition of arylboronic acids to α,β-unsaturated carbonyl compounds in aqueous media was developed with high yields.     

Silver triflate and triphenylphosphine co-catalyzed reactions of 2-alkynylbenzaldehyde, amine, and α,β-unsaturated ketone

A two-component activation system that combines metal catalysis (AgOTf) and the employment of catalytic amount of organocatalyst (PPh₃) has been successfully employed in the three-component reaction of 2-alkynylbenzaldehyde, amine, and α,β-unsaturated ketone. This reaction proceeds smoothly in THF under mild conditions leading to the functionalized 1,2-dihydroisoquinolines in moderate to good yields.     

Synthesis and curing behavior of alkyl-substituted poly(aryl ether ketone)s having a crosslinkable styryl group at chain ends

Crosslinkable alkyl-substituted poly(aryl ether ketone)s (PEKs) bearing a styryl group at both chain ends were synthesized by nucleophilic substitution reaction of 1,1′-(p-phenyl-enedioxy)bis[2-methyl-4-(4-fluorobenzoyl)benzene] with an excess aromatic diol in the presence of a base, followed by the reaction of the terminal phenol group with chloromethylstyrene. The aromatic diols used in this study were hydroquinone and resorcinol. The molecular weight of the polymer determined by GPC and ¹H NMR agreed with each other and close to the theoretical value calculated from the feed ratio. The polymer was soluble in N,N-dimethylacetamide and tetrahydrofuran, but insoluble in acetone and methanol. From DSC analysis, the polymer was thermally crosslinked around 220°C. The addition of dicumyl peroxide as a radical generator in the polymer decreased the curing temperature. The cured polymer showed high thermal stability up to 420°C under nitrogen. © 1997 John Wiley & Sons, Inc.     

A computational study on the mechanism for the GaCl3-catalyzed [4+1] cycloaddition of α,β-unsaturated ketone and 2,6-dimethylphenyl isocyanide

The reaction of the GaCl₃-catalyzed [4+1] cycloaddition of α,β-unsaturated ketone with 2,6-dimethylphenyl isocyanide leading to unsaturated γ-lactone derivative has been investigated using the density functional theory with the B3LYP hybrid functional. According to our calculations we found that the reaction is stepwise and exothermic. The reaction proceeds via three steps. The first step is the coordination of GaCl₃ to the oxygen atom in mesityloxide leading to a more electrophilic C3 atom. At the second step, 2,6-dimethylphenyl isocyanide attacks mesityloxide to form the C3-C6 bond with GaCl₃ activator, which is the rate-limiting step. Finally, the C6-O bond is formed to give the five-member cycle product due to the attack of the C6 atom to the O atom. In addition, our calculations also suggest that GaCl₃ activator can be easily detached from the product. The theoretical results are in good agreement with the recent experimental observations.     

Simultaneous construction of a polyether backbone and a variety of keto side chains by three‐component polycondensation: An improved method for the use of a variety of silyl enol ethers

For the synthesis of polyethers with a variety of keto side chains in a one‐step reaction, the three‐component polycondensation of dialdehydes, diol disilyl ethers, and silyl enol ethers of ketones was investigated. The method of monomer addition strongly affected the molecular weight of polymers and was optimized to yield high molecular weight polymers by model reactions. A variety of dialdehydes, diol disilyl ethers, and silyl enol ethers were polymerized in the presence of a catalytic amount of triphenylmethyl (trityl) perchlorate in CH₂Cl₂ at −78 °C according to the method of monomer addition. This polymer synthesis was unusual in that it concurrently constructed both the polyether backbone and the keto side chains from three starting compounds. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 179–188, 2000     

A novel transition metal-free conjugate reduction of α,β-unsaturated ketones with tosylhydrazine as a hydrogen source

A novel and efficient method has been developed for the chemoselective conjugate reduction of α,β-unsaturated ketones with tosylhydrazine as a hydrogen source to the corresponding saturated ketones in moderate to good yields. The present protocol does not require the use of transition metal, and is efficient being applicable to a wide range of substrates (25 examples).     

The synthesis and characterization of amine-terminated poly(aryl ether ketone)s as a function of side group and molecular weight

It is shown that amine-terminated poly(aryl ether ketone)s based on the reaction of 4,4'-difluorobenzophenone, and a substituted hydroquinone [either methylhydroquinone (MePK), t-butylhydroquinone (tBPK), or phenylhydroquinone (PhPK)] of controlled molecular weight and high amine-termination efficiency can be synthesized by a two-step reaction technique. Attempts to synthesize analogous materials by a one-step method were shown to be unsuccessful. The side groups are shown to have a large influence on the aromatic proton chemical shifts and this effect is characterized. The side groups and molecular weight are also shown to influence the thermal transitions of the respective polymers. The tBPK polymer possessed the highest glass transition temperature, while the MePK polymer was found to be the only semi-crystalline polymer; a unit cell is proposed. The side groups and molecular weight effects are also characterized as a function of thermal stability and mechanical properties. © 1994 John Wiley & Sons, Inc.