Catalytic conjugate additions of carbonyl anions under neutral aqueous conditions

The conjugate addition of carbonyl anions catalyzed by thiazolium salts that is fully operative under neutral aqueous conditions has been accomplished. The combination of alpha-keto carboxylates and thiazolium-derived zwitterions produces reactive carbonyl anions in a buffered protic environment that readily undergo conjugate additions to substituted alpha,beta-unsaturated 2-acyl imidazoles. The scope of the reaction has been examined and found to accommodate various alpha-keto carboxylates and beta-aryl substituted unsaturated 2-acyl imidazoles. The optimal precatalyst for this process is the commercially available thiazolium salt 5, a simple analogue of thiamin diphosphate. In this process, no benzoin products from carbonyl anion dimerization are observed. The corresponding 1,4-dicarbonyl compounds can be efficiently converted into esters and amides by way of activation of the N-methylimidazole ring via alkylation.     

An efficient protocol for acetalization of carbonyl compounds using Zr(HSO4)4 at room temperature under solvent-free conditions

Zr(HSO₄)₄ as a solid acid was applied for the acetalization of carbonyl compounds, at room temperature, under solvent-free conditions with good to excellent yields. The low cost and availability of the reagents, versatile procedure and easy work-up make this method attractive for the organic synthesis of these compounds.     

Substitution reactions of some polynuclear carbonyl anions

The reactions of [FeCo₃(CO)₁₂]^- and [MnFe₂(CO)₁₂]^- with a number of monodentate phosphorus donor ligands (L) are reported, and complexes of the type [FeCo₃(CO)₁₁L]^- and [MnFe₂(CO)₁₁L]^- have been isolated and characterised. Only with Ph₂PCH₂CH₂PPh₂ (DPPE) was it possible to replace more than one CO group, the complex [FeCo₃(CO)₁₀(DPPE)]^- being obtained. Protonation of the ironcobalt anions leads to the neutral hydrido clusters and is accompanied by a large kinetic isotope effect, although not as large as for [FeCo₃(CO)₁₂]^- itself. The reaction of [FeCo₃(CO)₁₂]^- with Ph₂C₂ gives [FeCo₃(CO)₁₀(Ph₂C₂)]^-.     

Stereoselective reactions of α-silylallyl anions with carbonyl compounds.

α-silylallyl anions of the type 6 react with carbonyl compounds at the γ-position, and stereoselectively to give the E- or Z-isomer depending on the reaction conditions. Solvent and reaction temperature play a critical role in the controle of stereoselectivity.     

Synthesis of polyfunctional aliphatic carbonyl compounds under phase-transfer conditions

We have studied mono- and dialkylation of malonic, acetoacetic, and cyanoacetic esters with esters of haloacetic and -halopropionic acids and addition of the CH acids mentioned and their analogs to methyl and ethyl acrylate under phase-transfer catalysis conditions, and also deethoxycarbonylation of the obtained products. We have demonstrated for the first time the possibility of Dieckmann cyclization under phase-transfer catalysis conditions and have developed a simple method for the synthesis of 2,3-di(ethoxycarbonyl)cyclopentanone, a key intermediate in the syntheis of deoxyprostaglandins, by cyclization of triethyl 1,2,4-butanetricarboxylate.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1073–1079, May, 1991.     

House bulb light-induced photochemical acetalization of carbonyl compounds catalyzed by Eosin Y

We have systematically studied the reactions of acetalization and found that high reaction efficiency can be achieved using cheap and readily available organic Eosin Y as catalyst. The reaction proceeds smoothly under house bulbs and shows excellent functional group tolerance. The substrates of the reaction system are compatible with aromatic aldehydes, aliphatic aldehydes, aromatic ketones, and cyclic ketones with high yields.     

Addition of anions to carbonyl compounds: an ab initio study

Energies for the addition of anionic nucleophiles, Z(-), to carbonyl compounds, XYCO, are calculated at the G2(MP2) level of theory. The substituents X, Y, and Z are taken from the set {H, CH3, NH2, OH, F, CF3, CHCH2, CHO, CCH, and CN}. The basicity and, to a lesser extent, ionization potential of Z(-) were found to correlate with the enthalpy of addition of Z(-) to H2CO. The enthalpy of addition of Z(-) to XYCO relative to H2CO is largely independent of Z. The ordering of the enthalpies of addition for the series of XYCO's is rationalized. By using a thermodynamic cycle, the independence of this ordering from Z is attributed to the additivity of the inductive stabilization of XYZCO(-) by X and Y versus H2ZCO(-). A method for estimating the enthalpy of addition for nucleophile/carbonyl combinations not studied above is described and shown to give good results on a model system.     

A facile procedure for acetalization under aprotic conditions

Carbonyl compounds are readily acetalized by alkoxysilanes in the presence of trimethylsilyl trifluoromethanesulfonate catalyst.     

Photochemical acetalization of carbonyl compounds in protic media using an in situ generated photocatalyst

Carbonyl compounds are conveniently converted into their corresponding dimethyl acetals in good yields and short reaction times by means of a photochemical reaction in methanol with a catalytic amount of chloranil (2,3,5,6-tetrachloro-1,4-benzoquinone, CA) as the sensitizer. Using aldehydes gives better results than using ketones, which also tend to form enol ethers as side products. These results are similar to those of simple acid-catalyzed acetalization reactions, suggesting the involvement of a photochemically generated acid. On the basis of steady state and laser flash photolysis data the reaction is proposed to involve the in situ generation of a photocatalyst (2,3,5,6-tetrachloro-1,4-hydroquinone, TCHQ) via reaction of CA with the solvent. The acetalization process is initiated by ionization of TCHQ, followed by loss of a proton to the solvent or the carbonyl, which starts a catalytic reaction. The photocatalyst is regenerated via a disproportionation reaction.     

Reaction of Grignard reagents with carbonyl compounds under continuous flow conditions

This contribution details how a continuous flow reactor was used to react carbonyl compounds with Grignard reagents at room temperature in an efficient and safe manner. Flow rate, residence time and temperature were optimized for the preparation of a small collection of secondary and tertiary alcohols. Excellent yields and general applicability were observed using the set-up protocol. The procedure was also applied for the preparation of Tramadol, an analgesic drug belonging to the opioid group. The developed conditions allowed the selective addition of Grignard reagents to aldehydes and ketones in the presence of a nitrile function.     

Gallium metal mediated allylation of carbonyl compounds and imines under solvent-free conditions

Gallium metal is effective in mediating the allylation of various carbonyl compounds and imines under solvent-free conditions, with the application of sonic energy, affording the corresponding homoallylic alcohols and amines. The imines themselves were also prepared under solventless conditions in high yield, thereby establishing a two-step solvent-free synthesis of homoallylic amines. In comparison, indium metal produced a mixture of the desired homoallylic secondary amine and the bis-allylated species via an iminium ion intermediate.     

Intermolecular rhodium(II)-catalyzed reactions with silicon-substituted carbonyl ylides

[reaction: see text] The Rh(II)-catalyzed reaction of benzyl 2-trialkylsilyl-2-diazoacetates with various acyclic and cyclic ketones affords novel dioxolanones via silicon-substituted carbonyl ylides in up to 98% yield.     

Experimental study of dimerization of radical anions of aromatic carbonyl compounds

The rate constants of dimerization (k₁) of radical anions of acetophenone, 1-acetylnaphthalene, 9-acetylanthracene, 9-formylanthracene, and anthracene in DMF containing 0.02 M tetrabutylammonium bromide were determined by differential cyclic voltammetry. It was shown that the values of k₁ of the radical anions investigated are correlated with the values of the boundary electron density on the reaction sites, which in turn increase symbatically with an increase in the size of the aryl fragment or on incorporation of electron-acceptor functional groups in the anthracene nucleus.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1777–1782, August, 1991.     

Pyrrolidine-diaminomethylenemalononitrile organocatalyst for Michael additions of carbonyl compounds to nitroalkenes under solvent-free conditions

The novel pyrrolidine-diaminomethylenemalononitrile organocatalyst 7 promotes the asymmetric conjugate addition of a carbonyl compound to a nitroalkene to afford the corresponding adduct in high yield with up to 99% ee, under solvent-free conditions.