Catalysis by ionic liquid: a simple, green and efficient procedure for the Michael addition of thiols and thiophosphate to conjugated alkenes in ionic liquid, [pmIm]Br

A room temperature ionic liquid, 1-pentyl-3-methylimidazolium bromide, [pmIm]Br efficiently catalyzes Michael addition of thiols and diethyl dithiophosphate to a variety of conjugated alkenes such as α,β-unsaturated carbonyl compounds, carboxylic esters, nitriles and chalcones without requiring any other organic solvent and catalyst. The ionic liquid can be recycled for subsequent reactions without any appreciable loss of efficiency.     

Catalysis by an ionic liquid: efficient conjugate addition of thiols to electron deficient alkenes catalyzed by molten tetrabutylammonium bromide under solvent-free conditions

An inexpensive and readily available ionic liquid, tetrabutylammonium bromide in the molten state, efficiently catalyzes the conjugate addition of thiols to α,β-unsaturated nitriles, carboxylic ester, ketones and aldehydes as well as nitro olefins.     

Ionic liquid as catalyst and reaction medium. The dramatic influence of a task-specific ionic liquid, [bmIm]OH, in Michael addition of active methylene compounds to conjugated ketones, carboxylic esters, and nitriles

[reaction: see text] A task-specific ionic liquid, [bmIm]OH, has been introduced as a catalyst and as a reaction medium in Michael addition. Very interestingly, although the addition to alpha,beta-unsaturated ketones proceeds in the usual way, giving the monoaddition products, this ionic liquid always drives the reaction of open-chain 1,3-dicarbonyl compounds with alpha,beta-unsaturated esters and nitriles toward bis-addition to produce exclusively bis-adducts in one stroke.     

Nickel Acetylacetonate-Induced 1,4-Additions of 1-Alkenyl(Disiamyl)Boranes to α,β-Unsaturated Ketones,Esters and Nitriles

The conjugate addition of 1-alkenyl(disiamyl)boranes to α,β-unsaturated ketones, esters, or nitriles was carried out in the presence of Ni(acac)₂ and triethylamine in DMF. The reactions provided γ,δ-unsaturated ketones, esters, and nitriles in high yields while retaining the original configuration of the 1-alkenylboranes. A similar addition reaction of 1-alkenyl(disiamyl)boranes to 1-acetyl-2-vinylcyclopropane produced the terminal and internal coupling products, 5,8-alkadien-2-on and 5-ethenyl-6-alken-2-on, in high yields in some cases with high regioselectivity favoring the terminal addition products.     

K2CO3-promoted domino reactions: construction of functionalized 2,3-dihydrobenzofurans and clofibrate analogues

The K(2)CO(3)-catalyzed domino reactions (Michael alkylation, Mannich alkylation, and aldol alkylation) of salicylic aldehyde derivatives (2-hydroxyaryl-α,β-unsaturated ketones, 2-hydroxyarylnitroalkenes, 2-hydroxyarylimines, and salicylic aldehydes) and 2-halo-1,3-dicarbonyl compounds (diethyl α-bromomalonate, diethyl α-chloromalonate, ethyl 2-chloroacetoacetate, and 3-chloropentane-2,4-dione) were carried out under mild conditions to provide a series of functionalized 2,3-dihydrobenzofurans in moderate to excellent yields. The novel transformations simultaneously gave a series of clofibrate analogues, which possess various substitution patterns.     

Convenient One-Pot Synthesis of β-Alkylthio Acid Derivatives from Thioacetates and the Corresponding α,β-Unsaturated Compounds

Various β-alkylthio acid derivatives were prepared conveniently from thioacetates and α,β-unsaturated compounds through borohydride exchange resin (BER)-Pd catalyzed transesterification of thioacetates to the corresponding thiols and Michael addition of the resulting thiols to α,β-unsaturated compounds.     

KF/Al2O3-Mediated Michael Addition of Thiols to Electron‐Deficient Olefins

Potassium fluoride supported on alumina efficiently catalyzes Michael addition of aromatic and aliphatic thiols to a variety of conjugated alkenes such as α,β‐unsaturated carbonyl compounds, carboxylic esters, amides, nitriles and chalcones. The Michael adducts are produced in good to excellent yields and relatively in short times. The catalyst can be recycled for subsequent reactions without any appreciable loss of efficiency.     

Enantioselective organocatalytic conjugate addition of α-nitroacetate to α,β-unsaturated ketones in water

The catalytic enantioselective conjugate addition reaction of α-nitroacetate to α,β-unsaturated ketones promoted by chiral bifunctional organocatalysts is described. The treatment of α-nitroacetate to α,β-unsaturated ketones under aqueous-phase reaction conditions afforded the corresponding Michael adducts with high enantioselectivity. The conjugate addition adducts are easily converted to chiral δ-keto nitroalkanes and δ-keto esters.     

Elementary Reactions of Metal Alkyl in Anionic Polymerization. III. Reaction Mode of n-Butylmagnesium Bromide with α,β-Unsaturated Carbonyl Compounds∗

Reaction modes of n-butylmagnesium bromide with α,β-unsaturated esters, ketones, and nitriles were investigated in ether under anionic polymerization conditions. n-Butane and conjugate addition products observed were with all the monomers examined, but carbonyl addition products were not detected except with the unsaturated esters. Product distribution depends mainly upon reaction temperature and the concentration of the Grignard reagent, not upon the concentration of the unsaturated compounds. n-Butyl-magnesium bromide etherate in toluene gave similar results.     

Computational mechanistic study of PMe3 and N-heterocyclic carbene catalyzed intramolecular Morita-Baylis-Hillman-like cycloalkylations: the origins of the different reactivity

It has been experimentally reported that PMe(3) catalyzes the cycloalkylation of the pendant halogenated α,β-unsaturated ketones (e.g., 1) at the C(α) position, whereas NHC catalyzes the cycloalkylation of the pendant halogenated α,β-unsaturated esters (e.g., 2) at the C(β) position. A DFT study has been performed to understand the detailed reaction mechanisms and the causes for the different ring closure positions in the two cycloalkylations promoted by the similar catalysts. Both reactions undergo three stages that include the nucleophilic addition of the catalysts (PMe(3) or NHC) to the substrates (1 or 2) and subsequent ring closure via S(N)2 mechanism, the H-elimination by the bases (KOH or K(3)PO(4)), and the catalyst release giving the final products. The first stage in the NHC-catalyzed reaction involves a favorable H-transfer step leading to the umpolung Michael acceptor, which is more stable than the nucleophilic addition complex. The H-transfer turns off the possibility to close ring at C(α) position for the reaction. In contrast, the similar H-transfer in the PMe(3)-catalyzed reaction is thermodynamically unfavorable. According to the electronic structure of the addition complex of PMe(3) to substrate (1), we rationalize why the experimentally isolated intermediate in the PMe(3)-catalyzed reaction is the trans-cyclic ketophosphonium salt, rather than its cis isomer that favors electrostatic attraction. The differences and the similarities among the two reactions and the traditional MBH reaction are discussed.     

Ceric ammonium nitrate (CAN) as a green and highly efficient promoter for the 1,4-addition of thiols and benzeneselenol to α,β-unsaturated ketones

A mild and efficient process for the 1,4-addition of thiols and benzeneselenols to various α,β-unsaturated ketones using a catalytic amount of CAN with excellent product yields is described. This inexpensive, nontoxic, and readily available catalytic ceric(IV) ammonium nitrate system efficiently catalyzes conjugate addition reactions between thiol derivatives and various α,β-unsaturated ketones under solvent-free conditions. A plausible mechanism for the role of CAN, both as a promoter in free radical chain addition reactions as well as a catalyst for the conjugate addition process is proposed.     

Effective methods for the syntheses of 2-pyrazolines and pyrazoles from diazocarbonyl compounds

Dipolar addition of diazocarbonyl compounds to α,β-unsaturated esters and nitriles in the presence of pyridine results in the production of 2-pyrazolines in nearly quantitative yields. In one case, reaction of α-diazoacetophenone with acrylonitrile, Michael addition of the 2-pyrazoline to the conjugated olefin is observed, but this process is minimized by limiting the amount of pyridine employed. 5-Cyano-2-pyrazolines are converted to derivative pyrazoles through alkoxide promoted hydrogen cyanide elimination. With vinyl sulfone, α-diazoacetophenone undergoes sequential dipolar addition, Michael addition, and vinyl sulfite elimination under exceptionally mild conditions to form the derivative β-(1-pyrazolyl)ethyl vinyl sulfone in good yield.     

Tandem reactions of 1,2-allenic ketones leading to substituted benzenes and α,β-unsaturated nitriles

One-pot double Michael addition/intramolecular aldol reaction/decarboxylation of 1,2-allenic ketones with cyanoacetate offers an efficient and convenient approach to highly functionalized benzenes. With 2-substituted cyanoacetates, the reaction proceeds via a different tandem process to afford α,β-unsaturated nitriles effectively.     

Conjugate addition of indoles to α,β-unsaturated ketones using Cu(OTf)2 immobilized in ionic liquids

Indoles undergo smooth conjugate addition with α,β-unsaturated ketones in the presence of 10 mol% copper(II) triflate immobilized in air and moisture stable [bmim]BF₄ ionic liquid under mild conditions to afford the corresponding conjugate addition products in high to quantitative yields. The recovery of Cu(OTf)₂ is facilitated by the ionic liquid. The recovered catalyst was reused four to five times with consistent activity.     

Enantioselective conjugate addition of fluorobis(phenylsulfonyl)methane to α,β-unsaturated ketones catalyzed by chiral bifunctional organocatalysts

The catalytic enantioselective conjugate addition reaction of fluorobis(phenylsulfonyl)methane to α,β-unsaturated ketones promoted by chiral bifunctional organocatalysts is described. The treatment of fluorobis(phenylsulfonyl)methane to α,β-unsaturated ketones under mild reaction conditions afforded the corresponding Michael adducts with high enantioselectivity. The conjugate addition adducts are useful for the synthesis of chiral monofluoromethylated compounds.     

Catalyzed Addition of Aldehydes to Activated Double Bonds—A New Synthetic Approach

In the presence of cyanide ions as catalyst, aromatic and heterocyclic aldehydes can be smoothly added to α,β-unsaturated ketones, esters, and nitriles in aprotic solvents to form γ-diketones, 4-oxo carboxylic esters, and 4-oxo nitriles. Thiazolium salts in the presence of bases are also suitable catalysts; they permit not only addition of aromatic and heterocyclic aldehydes but also the addition of aliphatic aldehydes.     

N-heterocyclic carbene catalyzed reactions of α-bromo-α,β-unsaturated aldehydes/α,β-dibromoaldehydes with 1,3-dinucleophilic reagents

Carbenes ring true: N-Heterocyclic carbene (NHC) catalyzed reactions of α-bromo-α,β-unsaturated aldehydes/α,β-dibromoaldehydes with 1,3-dinucleophilic reagents, such as 1,3-dicarbonyl compounds, β-enamino ketones, and β-enamino esters through umpolung processes gave functionalized 3,4-dihydropyranones and 3,4-dihydropyridinones. The availability of the starting materials, lack of external oxidant, and usefulness of the products make this strategy attractive.     

New synthetic methods for α,β -unsaturated ketones,aldehydes, esters and lactones by the palladium-catalyzed reactions of silyl enol ethers,ketene silyl acetals,and enol acetates with allyl carbonates

Silyl enol ethers and ketene silyl acetals derived from ketones, aldehydes, esters and lactones are converted into α,β-unsaturated ketones, aldehydes, esters and lactones by treatment with allyl carbonates in high yields using the palladium—bis(diphenylphosphino)ethane (dppe) complex as catalyst. Phosphine-free palladium catalyst instead of the palladium—phosphine complex gives a higher selectivity for the preparation of cyclopentenone, cyclooctenone, dienones, α,β-unsaturated esters and lactones. As a solvent, the use of nitriles such as acetonitrile is essential. In other solvents, allylation takes place. Enol acetates derived from ketones are converted into α,β-unsaturated ketones by reaction with allyl carbonate in acetonitrile using the palladium complex and tributyltin methoxide as bimetallic catalysts.     

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.     

ZrOCl2·8H2O on montmorillonite K10 accelerated conjugate addition of amines to α,β-unsaturated alkenes under solvent-free conditions

At room temperature, ZrOCl₂·8H₂O on montmorillonite K10 efficiently catalyzes conjugate addition of amines to a variety of conjugated alkenes such as α,β-unsaturated carbonyl compounds, carboxylic esters, nitriles and amides under solvent-free conditions. The catalyst can be recycled for subsequent reactions without any appreciable loss of efficiency.