Kinetic scheme of homogeneous acid-catalyzed transformation of isopentenols

The reactions occurring in an equilibrium mixture of 3-methyl-1-buten-3-ol and 3-methyl-2-buten-1-ol in 24–49 % aqueous solutions of H₂SO₄ yield isoprene, 3-methyl-3-buten-1-ol, isobutylene, formaldehyde, 3-methylbutane-1,3-diol. Isobutylene is rapidly hydrated to give 2-methylpropan-2-ol. The presence of formaldehyde in the reaction mixture indicates that the transformations involve the reverse Prins reaction. On the basis of experimental and literature data, two most probable reaction schemes were suggested.Translated fromIzvestiya Akademii Nauk. Sertya Khimicheskaya, No. 5, pp. 867–870, May, 1995.     

The kinetics of acid-catalyzed decomposition of decanepersulfonic acid

The kinetics of thermal decomposition of decanepersulfonic acid (RSO₂OOH, R=C₁₀H₂₁) in CCl₄ in the presence of cyclohexanesulfonic and trifluoroacetic acids at 323–343 K was studied. The reaction has an autocatalytic character. The kinetics of consumption of the persulfonic acid is described by the equation-d[RSO₂OOH]/dt=k ₁[RSO₂OOH]+k ₂[RSO₂OOH]·[HX]. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 202–203, January, 1999.     

New observation on a class of old reactions:Chemoselectivity for the solvent-free reaction of aromatic aldehydes with alkylketones catalyzed by a double-component inorganic base system

Solvent-free reactions of aromatic aldehydes with three representative ketones,including acetophenone,acetone and cyclohexanone,have been examined under the catalysis of a low-cost inorganic base system consisting of NaOH and K2CO3.It was found that the chemoselectivity of the reactions is in close relationship with the composition of the reactants and the doublecomponent catalyst.Under the optimized experimental conditions,1,2,3,4,5-pentasubstituted cyclohexanols,α,β-unsaturated ketones and Claisen-Schmidt...     

Chiral phosphoric acid-catalyzed enantioselective three-component Mannich reaction of acyclic ketones,aldehydes and anilines

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Brønsted acid-catalyzed C-C bond forming reaction for one step synthesis of oxazinanones

An efficient Brønsted acid-catalyzed synthesis of oxazinanones (2) from corresponding Boc-imines (1) in one-step has been developed. Oxazinanones are obtained via an unprecedented tandem elimination-cycloaddition reaction. The reaction is remarkably significant given its novelty, mild reaction conditions, simplicity and low cost of the catalyst system.     

Asymmetric sp C-H functionalization via a chiral Brønsted acid-catalyzed redox reaction for the synthesis of cyclic aminals

An organocatalytic asymmetric tandem 1,5-hydride transfer/ring closing reaction of o-aminobenzoketones with anilines to give cyclic aminals in fairly good diastereo- and enantioselectivities.     

A very high yielding and facile alkaline earth metals homogeneous catalysis of Biginelli reaction: an improved protocol

Abstract

A high yielding and facile Biginelli reaction for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones and thiones, using inexpensive and available alkaline earth metal chlorides (MgCl₂, CaCl₂, SrCl₂ and BaCl₂) and acetic acid as the solvent in a homogeneous catalytic reaction, is reported.     

The thermal decomposition of the carbonate reaction products

The complex thermal analysis was used in the investigations of the carbonate reaction products in the residue after Al leaching from calcium aluminate-12CaO·7Al₂O₃ and Selfdisintegrated Powder. The conversion of Al was calculated basing on a content of Al in the pregnant solution as well as in a residue obtained from the kinetic investigations. The third method of measurements of a conversion of Al was presented and discussed. Results show, that the proposed method can be used for conversion estimations with 95% of confidence level as well as for the detection of carbonate products and is useful for an interpretation of the new approach for kinetic mechanism of Al leaching.     

Triflic acid-catalyzed cascade cyclization of arenyl enynes via acetylene-cation cyclization and Friedel-Crafts type reaction

A novel triflic acid-catalyzed cascade cyclization of arenyl 1,7-enynes through acetylene-cation cyclization followed by Friedel-Crafts reaction has been described. Various fused poly carbocycles can be obtained in good to high yields under mild reaction conditions.     

Heterogeneous decomposition ofp-methoxy- andp-methyl-dibenzoyl peroxides by a montmorillonite amine intercalate

A kinetic study of the heterogeneous thermal decomposition ofp-MeO-DBP andp-Me-DBP catalysed by the montmorillonite benzidine intercalate has been made. The kinetics of decomposition were observed to follow a three-halves order reaction with respect to the peroxides. The activation parameters in heterogeneous media have lower values compared with the corresponding values in homogeneous ones. The relationships between H ^* and S ^* were plotted and show two converging straight lines which indicate that both electron donating and withdrawing substituents on the peroxide enhance the rate of decomposition under these conditions.     

Multisite catalysis: a mechanistic study of beta-lactone synthesis from epoxides and CO--insights into a difficult case of homogeneous catalysis

Carbonylation of epoxides with a combination of Lewis acids and cobalt carbonyls was studied by both theoretical and experimental methods. Only multisite catalysis opens a low-energy pathway for trans opening of oxirane rings. This ring-opening reaction is not easily achieved with a single-site metal catalyst due to structural and thermodynamic constraints. The overall reaction pathway includes epoxide ring opening, which requires both a Lewis acid and a tetracarbonylcobaltate nucleophile, yielding a cobalt alkyl-alkoxy-Lewis acid moiety. After CO insertion into the Co-C(alkyl) bond, lactone formation results from a nucleophilic attack of the alkoxy Lewis acid entity on the acylium carbon atom. A theoretical study indicates a marked influence of the Lewis acid on both ring-opening and lactone-formation steps, but not on carbonylation. Strong Lewis acids induce fast ring opening, but slow lactone formation, and visa versa: a good balance of Lewis acidity would give the fastest catalytic cycle as all steps have low barriers. Experimentally, carbonylation of propylene oxide to beta-butyrolactone was monitored by online ATR-IR techniques with a mixture of tetracarbonylcobaltate and Lewis acids, namely BF(3), Me(3)Al, Et(2)Al(+).diglyme, and a combination of Me(3)Al/dicobaltoctacarbonyl. We found that the last two mixtures are extremely active in lactone formation.     

用固体碱催化Michael加成反应的研究

Different Michael addition reactions catalyzed by solid base K2O/γ-Al2O3 and KF/γ-Al2O3, MgO/γ-Al2O3 prepared by microwave irradiation method were reported in this paper. For the K2O/γ-Al2O3, not only good yield was attained but also made the reaction of Acetonitrile that usually is regarded as inactive carbonion and α, β-unsatumted compound to carry out. The yield of Michael reaction of Ethyl acetoacetate and Crotonaldehyde catalyzed by KF/γ-Al2O3, MgO/γ-Al2O3, MgO/NaY all could reach to 80% and the latter could reach to 90%. At the same time, the catalysts of different content(the ratio of load) of MgO were also applied in this reaction, and it was found that the best content of MgO was 20% ～ 25%。     

Lewis acid-catalyzed asymmetric hydroxymethylation of silicon enolates in aqueous media

Asymmetric hydroxymethylation of silicon enolates with formaldehyde in aqueous media has been achieved using praseodymium triflate and a chiral crown ether. Formaldehyde aqueous solution can be directly used for the reactions, and a water/THF mixture was found to be the best solvent system. This is the first example of catalytic asymmetric hydroxymethylation of silicon enolates.     

Brönsted acid-catalyzed synthesis of diarylmethanes under non-genotoxic conditions

Triflic acid and triflimide were found to efficiently catalyze the formation of a wide diversity of diarylmethanes from the non-genotoxic benzylic acetates and electron-rich arenes or heteroarenes. The reaction worked best with acetates capable of generating a stabilized benzylic cationic species. In most cases, the reactions were conveniently run in the absence of solvent under mild conditions.     

Catalytic asymmetric synthesis of spirooxindoles by a mannich-type reaction of isothiocyanato oxindoles

Easy access: a strontium/Schiff base complex as catalyst for the title reaction provided straightforward access to enantiomerically enriched spiro[imidazolidine-4,3'-oxindole] compounds, as well as a spiro[imidazoline-4,3'-oxindole] through a two-step conversion from the Mannich adduct.     

Amino acid-catalyzed direct enantioselective synthesis of β-amino-α-oxyaldehydes

The first direct amino acid-catalyzed asymmetric syntheses of α-oxy-β-aminoaldehydes are presented. The organocatalytic Mannich reactions between unmodified α-oxyaldehydes and anilines proceeded with excellent enantioselectivities. In most cases, the corresponding α-oxy-β-aminoaldehyde adducts were isolated in high yield with excellent chemo- and enantioselectivity. For example, orthogonally protected 3-amino-tetroses and α-amino acid derivatives were isolated in up to >99% ee.     

Macrocycles from simple building blocks by a multifold Heck-type coupling reaction

Diiodobenzenes and bisallylic alcohols—two equivalents of each—were coupled under palladium catalysis to give oxofunctionalized macrocycles as 2:2 products. The 1:1 products as medium sized rings were disfavoured and not observed.     

Heterogeneous synergistic catalysis by a palladium complex and an amine on a silica surface for acceleration of the tsuji-trost reaction

The cooperative surface-catalysis strategy of a Br?nsted acid and an organic base can be extended to a metal complex and organic base pair. A silica-supported diaminopalladium complex and a tertiary amine were prepared and characterized. The Pd-catalyzed Tsuji-Trost reaction was enhanced significantly by the presence of the tertiary amine on the same silica surface as the Pd complex.