Search results for "acid catalysis"

Using theozymes for designing transition-state analogs for the intramolecular aldol reaction of δ-diketones

2001

Two theozymes for the intramolecular aldol reaction of δ-diketones have been studied using ab initio methods. The presence of both acid/base residues favors several steps of the aldol reaction. The appropriate positioning of these residues can accelerate one of two diastereromeric reaction pathways, the catalyzed aldol reaction being highly stereoselective. Analysis of the geometrical parameters, charge distribution, and the shape of molecular electrostatic potential for the corresponding acid/base catalyzed transition structure allows us to design adequate transition-state analogs to favor a reactive channel of this intramolecular aldol reaction. © 2001 John Wiley & Sons, Inc. Int J Quant …

Cationic mono- and bi-nuclear iron complexes as Lewis acid catalysts in Mukaiyama reactions

1992

Organometallic Lewis acids derived from photolysis of mono- and bi-nuclear cationic iron carbonyl complexes function as excellent catalysts for the Mukaiyama aldol reaction.

MINDO/3 Study of the Rearrangement of 1-Methylcyclohexyl Cation to 1,2-Dimethylcyclopentyl Cation

1986

The rearrangement of the 1-methylcyclohexyl cation to the 1,2-dimethylcyclopentyl cation has been studied by MINDO/3 calculations, as an application of the branching mechanism model for cycloalkanes. Possible intermediates and transition states have been characterized by diagonalization of their Hessian matrixes. Two nonequivalent pathways, α and β scissions, are relatively close in energy. The calculated transition states are almost equivalent in energy to those found for cyclohexyl cation. Hence, the energy barriers are higher for the rearrangement of the 1-methyl than for cyclohexyl cation, because the former is less stable than the latter.

The Pd3(dppm)3(CO)2+ Cluster: An Efficient Electrochemically Assisted Lewis Acid Catalyst for the Fluorination and Alcoholysis of Acyl Chlorides.

2002

The dicationic palladium cluster Pd3(dppm)3(CO)2+ (dppm = bis(diphenylphosphino)methane) reacts with acid chlorides RCOCl (R = n-C6H13, t-Bu, Ph) to afford quantitatively the chloride adduct Pd3(dppm)3(CO)(Cl)+ and the acyl cation RCO+ as the organic counterpart. The dicationic reactive cluster can be reformed by electrolyzing the chloride complex with a copper anode leaving CuCl as a byproduct. The combination of these two reactions provides an electrocatalytic way to form the acylium from the acid chloride. Indeed, in CH2Cl2, 0.2 M NBu4PF6, or NBu4BF4, the electrolysis of the acid chloride in the presence of a catalytic amount of the cluster (1%) gives in good yields the acid fluoride RCO…

A molecular electron density theory study of the Lewis acid–catalyzed decomposition reaction of nitroethyl benzoate using aluminum derivatives

2019

Catalytic Dehydration of Fructose to 5-Hydroxymethylfurfural in Aqueous Medium over Nb2O5-Based Catalysts

2021

The catalytic dehydration of fructose to 5-hydroxymethylfurfural (HMF) in water was performed in the presence of pristine Nb2O5 and composites containing Nb and Ti, Ce or Zr oxides. In all experiments, fructose was converted to HMF using water as the solvent. The catalysts were characterized by powder X-ray diffraction, scanning electron microscopy, N2 physical adsorption, infrared and Raman spectroscopy and temperature-programmed desorption of NH3. Experimental parameters such as fructose initial concentration, volume of the reacting suspension, operation temperature, reaction time and amount of catalyst were tuned in order to optimize the catalytic reaction process. The highest selectivit…

2H -[1,3]Oxazino[3,2-α]indolin-4(3H )-ones: A Class Of Polyheterocyclic Indole-Based Compounds

2018

The Reactions of Electron-Rich Heterocycles with Derivatives of Orthocarboxylic Acids; VIII. Proton Acid-Catalyzed Acylation of Indoles by 2-Alkoxy-1…

1987

In acid-catalyzed reactions with 3-unsubstituted indoles 1, 2-alkoxy-1,3-dioxolanes 2a-c behave as acyl equivalents. Depending on the substitution patterns of the reaction partners, the 1,3-dioxolanium ions 3a-c, generated in situ from the cyclic ortho esters by the action of sulfosalicylic acid, react to form tris-(3-indolyl)alkanes 6 and 9, bis-(3-indolyl)ethenes 7, or 3-benzoylindoles 8. Analogous reactivity was observed with related acyclic ortho esters. Reaktionen elektronenreicher Heterocyclen mit Orthocarbonsaure-Derivaten; VIII. Protonsaurekatalysierte Acylierung von Indolen mit 2-Alkoxy-1,3-dioxolanen 2-Alkoxy-1,3-dioxolane 2a-c reagieren als Acylaquivalente mit 3-unsubstituierten …

Regioselective proton-catalyzed diarylmethylation of indoles with 9H-xanthydrol, dibenzosuberenol, and bis[4-dimethylaminophenyl]methanol

1988

3-Isopropylindole (4) is xanthenylated both at N-1 (stereocontrolled major reaction), C-2, and on the phenyl nucleus of the indole skeleton by xanthydrol (1). Other carbinols such as dibenzosuberenol (2) and bis[4-dimethylaminophenyl]methanol (3) with lower electrophilic SN1 activities than 1 do not react with 4 but do react very selectively with simple methylindoles to form diarylmethylated derivatives.

A Synthetic Model for the [4+2] Cycloaddition in the Biosynthesis of the Brevianamides, Paraherquamides, and Related Compounds

2000

Abstract The reactivity of model systems for the proposed [4+2] cycloaddition in the biosynthesis of the brevianamides, paraherquamides, and marcfortines is explored. The model for the intermolecular reaction reveals that the cycloaddition takes place under mild conditions only if activated, very reactive dienophiles are used. When relatively unreactive dienophiles such as cyclopentene and cyclohexene are used, harsh reaction conditions and/or a Lewis acid catalyst are necessary for the reaction. In contrast, the model for the intramolecular reaction demonstrates that the cycloaddition takes place within a few hours at room temperature, even in the absence of a Lewis acid catalyst. Conclusi…