Meerwein Ponndorf Verley Reaction Research Articles

Reduction of heterocyclic carboxaldehydes via Meerwein–Ponndorf–Verley reaction

A series of Mg/Al and Mg/Al/Zr layered double hydroxides (LDHs) was prepared for use as catalysts in the Meerwein–Ponndorf–Verley (MPV) reaction of heterocyclic carboxaldehydes. Analysis of the solids revealed that zirconium is in fact incorporated into the LDH structure; as a result, their calcination produces Mg/Al/Zr oxides that are effective catalysts for the MPV reduction of heterocyclic compounds. In fact, the catalysts thus obtained exhibited higher activity than a catalyst obtained from an LDH containing Mg and Al only. The reaction was conducted under very mild conditions (viz. atmospheric pressure and a temperature of 82 °C) and provided conversions close to 90 and 100% selectivity in all instances.

A concise synthetic route to optically active cis-β,γ-disubstituted-γ-butyrolactones via tandem Michael–MPV reaction: new total synthesis of (−)- cis-whisky lactone and (−)- cis-cognac lactone

Optically active cis-β,γ-disubstituted-γ-butyrolactones, for example, cis-whisky lactone and cis-cognac lactone, were readily synthesized by using tandem Michael–Meerwein–Ponndorf–Verley reactions that employed (−)-10-mercapto-isoborneol as a chiral template in the key step.

Bimetallic isopropoxides M[Al(OC3Hi7)4]3 (M = Pr, Nd)—catalyzed reduction of 2-octanone and benzophenone

Bimetallic alkoxides of praseodymium and neodymium with aluminum, viz., M[Al(OC(3)H(i)(7))(4)](3), where M = Pr(III)/Nd(III), have been used as catalysts in Meerwein-Ponndorf-Verley (MPV) reduction of 2-octanone and benzophenone in isopropanol to give their corresponding secondary alcohols. The reduction of ketones is investigated by following the absorption spectra involving 4f-4f transitions. During the MPV reduction the oscillator strengths (P) and the Judd-Ofelt intensity (T(lambda), lambda = 2,4,6) parameters corresponding to each 4f-4f band (H43-->D21, H43-->P03, H43-->P13, and H43-->P23 in praseodymium, and I9/24-->F3/24, I9/24-->F5/24, I9/24-->F7/24, I9/24-->G5/24, and I9/24-->G7/24 in neodymium alkoxides) at different time intervals have also been calculated and used in the determination of rates. Rates were calculated in terms of complexation of ketone and isopropanol with M[Al(OC(3)H(i)(7))(4)](3) during the MPV reaction, from the changes in both absorbance and oscillator strength with time, and were found to be comparable, verifying the Judd-Ofelt theory. The stronger oxyphilicity of Pr(III) and Nd(III) in M[Al(OC(3)H(i)(7))(4)](3) than of their analogue Al(III) in Al(OC(3)H(i)(7))(3) made the bimetallic alkoxides better catalyst in MPV reduction of ketones.

Catalytic Meerwein-Ponndorf-Verley (MPV) and Oppenauer (OPP) Reactions: Remarkable Acceleration of the Hydride Transfer by Powerful Bidentate Aluminum Alkoxides

A highly efficient catalytic procedure for Meerwein-Ponndorf-Verley (MPV) reduction has been devised by employing (2,7-dimethyl-1,8-biphenylenedioxy)bis(dialkoxyaluminum) (3) as a catalyst. For example, reduction of 4-phenylcyclohexanone in CH 2 Cl 2 with i-PrOH (1 equiv) as a hydride source in the presence of a catalytic amount of the in situ generated 3a ( 1 mol%) smoothly proceeded at room temperature within I hour to furnish 4-phenylcyclohexanol in 82% isolated yield. In sharp contrast, the conventional MPV reduction with stoichiometric Al(i-PrO) 3 resulted in the recovery of the starting ketone under similar conditions. Our approach also enabled the reverse reaction of MPV reduction, i.e., Oppenauer (OPP) oxidation in a truly catalytic manner. Furthermore, these findings prompted us to develop a simultaneous intramolecular reduction/oxidation of hydroxy carbonyl substrates via the MPV reaction process in the presence of bidentate aluminum catalyst 1, where highly chemoselective hydride transfer from a secondary alcohol moiety to the remote carbonyl group took place. Finally, we demonstrate that the modern MPV system is applicable to highspeed, catalytic Tishchenko reactions. For instance, the dimerization product of cyclohexanecarbaldehyde was obtained in almost quantitative yield using only 0.2 mol% of catalyst 3a. Based on this result, highly stereoselective intramolecular Tishchenko reduction of a β-hydroxy ketone was also accomplished successfully.

Al‐Free Zr‐Zeolite β as a Regioselective Catalyst in the Meerwein—Ponndorf—Verley Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Gas-phase Meerwein–Ponndorf–Verley reaction: correlation of the 3665 cm −1 IR band with the cis-alcohol selectivity

The two Lewis acid sites assumed to catalyze the Meerwein–Ponndorf–Verley (MPV) reaction are identified by IR bands at 3782 and 3660–3680 cm −1. Different combinations of heat-treatment protocols were used and the results indicated that the final temperature, ramp rate, and gas environment make a difference in the relative intensities of the 3782 and 3665 cm −1 bands. Combining different heat-treatment procedures, samples were produced where the 3782 and 3665 cm −1 band intensities moved in opposite directions (i.e., one increasing and the other decreasing). The MPV reduction of 4- tert-butylcyclohexanone with 2-propanol in the gas phase was studied at 100 °C in a nitrogen atmosphere. The increasing trend of the relative intensity of the 3665 cm −1 band showed a correlation in favor of the formation of cis-4- tert-butylcyclohexanol ( cis-4-TBCHL). This suggests that the species associated with the 3665 cm −1 band are likely responsible for cis-4-TBCHL selectivity.

Catalytic Applications of Aluminum Isopropoxide in Organic Synthesis

AbstractFor Abstract see ChemInform Abstract in Full Text.

Al-free Zr-zeolite beta as a regioselective catalyst in the Meerwein-Ponndorf-Verley reaction.

Al-free Zr-zeolite beta catalyzes the transfer reduction of ketones to the corresponding alcohols in high yield and with exceptional stereocontrol. Notably, the catalyst is very robust and gives good results even with 10% water content in the reaction mixture.

Influence of the preparation method on the structural and surface properties of various magnesium oxides and their catalytic activity in the Meerwein–Ponndorf–Verley reaction

The Meerwein–Ponndorf–Verley (MPV) reaction of cyclohexanone with isopropyl alcohol, which yields cyclohexanol, was studied by using basic catalysts consisting of magnesium oxide. The oxides were prepared using various synthetic procedures including calcination of commercially available magnesium hydroxide and carbonate, calcination of magnesium hydroxides obtained from magnesium nitrate and sulphate, the sol–gel technique and precipitation by decomposition of urea. The solids thus obtained were characterized structurally by X-ray diffraction spectroscopy and their surface properties determined using gas adsorption measurements (of nitrogen for textural properties and carbon dioxide for basic properties). Based on the results, the most active catalyst was the solid prepared by rehydration and subsequent calcination of a magnesium oxide that was previously obtained from commercially available magnesium hydroxide.

Hydrous Zirconia as a Selective Catalyst for the Meerwein–Ponndorf–Verley Reduction of Cinnamaldehyde

Hydrous zirconia was found to be active in the Meerwein–Ponndorf–Verley (MPV) reduction of cinnamaldehyde with 2-propanol. An initial selectivity to cinnamyl alcohol of higher than 97% was measured. At longer reaction times, etherification between cinnamyl alcohol and 2-propanol decreased the selectivity. The activity decreased sharply when the hydrous zirconia was calcined to higher temperatures. Surface hydroxyl groups are postulated to be important for the activity. They are required for ligand exchange with 2-propanol. Zirconium 1-propoxide grafted on silica, siliceous MCM-41, and Al-MCM-41 were also active in the MPV reaction. In contrast, zeolite beta, although active in the conversion of cinnamaldehyde, showed poor selectivity toward the desired product, cinnamyl alcohol. Instead, the main product formed was cinnamyl 2-propyl ether.

Activity of Basic Catalysts in the Meerwein–Ponndorf–Verley Reaction of Benzaldehyde with Ethanol

The Meerwein–Ponndorf–Verley (MPV) reaction of benzaldehyde with ethanol in the liquid phase in the presence of basic catalysts consisting of magnesium oxide, calcium oxide, and mixed oxides obtained by calcination of layered double hydroxides, was studied. The catalysts were characterized using various techniques including X-ray diffraction and gas adsorption (viz nitrogen physisorption to determine textural properties and carbon dioxide chemisorption to elucidate surface basic properties). The catalyst consisting of calcium oxide, which was that possessing the highest density of basic sites, was found to be the most active in the process; the MPV reaction was accompanied by two other, competing reactions (viz aldol condensation and the Tishchenko cross-reaction). The MPV reaction of benzaldehyde with other alcohols was also examined, the highest conversion being obtained with secondary alcohols as hydrogen sources.

Plutonium(III)-catalyzed Meerwein–Ponndorf–Verley reactions

The reactivity of Th(IV), U(III), U(IV), Pu(III) and Pu(IV) iso-propoxide in the Meerwein–Ponndorf–Verley reduction of ketones by iso-propanol have been examined. Plutonium(III) iso-propoxide is found to be an effective catalyst for the reduction of a range of substituted aryl-alkyl ketones, while An(IV) iso-propoxides (An=Th, U, Pu) are found to be inactive. U(III) was found to oxidize under the reaction conditions to a U(IV) complex, which was also catalytically inactive.

Preparation, Characterization, and Reactions of [(EDBP)Al(μ-OiPr)]2, a Novel Catalyst for MPV Hydrogen Transfer Reactions

The reaction of [(μ-EDBP)AlMe]2 (EDBP-H2 = 2,2‘-ethylidenebis(4,6-di-tert-butylphenol) with 2 mol equiv of 2-propanol at ambient temperature yields [(EDBP)Al(μ-OiPr)]2 (1), which has shown excellent catalytic activities toward hydrogen transfer reactions between aldehydes and 2-propanol (Meerwein−Ponndorf−Verley (MPV) reactions). The addition of 4 mol equiv of benzaldehyde, 4-methoxybenzaldehyde, or 4-chlorobenzaldehyde to [(EDBP)Al(μ-OiPr)]2 yields [(EDBP)Al(μ-OBz-p-X)(OCHC6H4-p-X)]2 (2, X = H; 3, X = OMe; 4, X = Cl). However, in the reaction of 1 with excess 4-nitrobenzaldehyde, only the four-coordinated complex [(EDBP)Al(μ-OBz-p-NO2)]2 (5) was obtained. Complex 1 further reacts with 2 mol equiv of OPPh3 or hexamethylphosphoramide (HMPA), yielding the four-coordinated monomeric complex [(EDBP)Al(OiPr)(S)] (6, S = OPPh3; 7, S = HMPA). Compounds 1, 3, 6, and 7 have been characterized by X-ray crystal structure determinations, enabling us to describe the intermediate of the MPV reactions.

Vapour-Phase Reaction of Acetophenone with Methanol or Dimethyl Carbonate on Magnesium Oxide and Magnesium Phosphates

The vapour-phase reaction of acetophenone with methanol on magnesium oxide, various magnesium phosphates, and combinations of the two types of catalysts was studied. The process was found to involve the Meerwein–Ponndorf–Verley reaction, aldol condensations, dehydrations, and hydrogenations. The presence of basic sites is indispensable for the reaction to develop; however, acid sites also play an active role. The selectivity for each reaction product depends on the particular catalyst used. The total conversion is maximal with the catalysts containing the largest populations of acid and basic sites. Also, catalysts with large numbers of acid sites exhibit an increased selectivity towards the corresponding alkenes. The use of dimethyl carbonate instead of methanol alters the reaction selectivity to an extent dependent on the particular catalyst and operating conditions. However, this also results in markedly decreased total conversion in some instances.

Relation between structure and Lewis acidity of Ti-Beta and TS-1 zeolites: A quantum-chemical study

Ab-initio Hartree–Fock and density-functional-theory quantum-chemical calculations have been carried out to characterise the geometry and LUMO energies of two zeolites, Ti-Beta and TS-1. The cluster model has been used and results from classical force-field calculations have also been included for comparison and to guide the definition of the cluster boundaries. The LUMO energy, which is related to the Lewis acidity, is shown to be different for the different T-sites, and, in general, Ti-Beta shows higher Lewis acidity than TS-1. This can explain their behaviour for epoxidation of olefins as well as their catalytic properties for Lewis acid-catalysed reactions such as Meerwein–Ponndorf–Verley reactions.

Meerwein–Ponndorf–Verley reaction of α-ketoepoxides. A stereocontrolled one-step synthesis of epoxy-1,3-diol monoesters

Lithium enolate 3, derived from ketoepoxide 1, adds to two molecules of an aldehyde with concomitant hydride transfer to produce 5 stereospecifically.

Catalysis of organic reactions by molecular sieve systems: 1. Meerwein-Ponndorf-Verley reductions

n-C 5 – C 12 alkanals underwent highly selective (9̆9% at 100 °C) Meerwein-Ponndorf-Verley (MPV) reduction in a continuous flow reactor, by applying as reducing agent a two-component hydrogen-transfer system consisting of NaX-type zeolite and isopropanol. Citronellal (1), which contains a Δ 6,7 double bond, underwent with MX-isopropanol systems (where M = alkali or alkaline-earth cation) two competing reactions, i.e., cyclization to isopulegol (2) or normal MPV reduction to citronellol (3). The direction of the reaction can be fully controlled by the type of exchangeable metallic ion in the X-type zeolite, CsX, yielding the MPV reduction product 3 with a selectivity of 92.3% at 150 °C, while LiX, NaX and CaX preferentially produce the cyclic compound 2. Non-substituted and alkyl-substituted cycloalkanones, having 4- to 15-membered rings were also investigated. The relative MPV conversions to the corresponding cycloalkanols at 100 °C and 180 °C were found to depend on the size of the ring system and, for substituted cycloalkanones, on the position and size of the alkyl substituent. Steric effects due to the geometry of the zeolite intracrystalline channel were also indicated. A limit in the applicability of the MPV reaction was reached with cyclopentadecanone, which was resistant to reduction. A mechanistic scheme for the zeolite-catalyzed MPV reductions is proposed.

The reduction of α,β‐unsaturated carbonyl compounds by the meerwein—ponndorf—verley method: The cause of low yields

AbstractThe main cause of low yields in the formation of allylic alcohols from unsaturated carbonyl compounds by the Meerwein—Ponndorf—Verley reaction has been found to be polymerisation of the product by acidity arising from small amounts of chloroalkoxides which occur in most alkoxides. Hot alkaline processing of crude reduction products effectively removes chloroalkoxides and leads to high yields of the allylic alcohols. The present work relates to the preparation of cinnamyl alcohol but it is applicable to other α,β‐unsaturated carbonyl compounds.

Stereochemistry of reduction of (–)-thujone and (—)-isothujone

The title compounds have been converted into mixtures of isomeric thujols by seven aluminium and boron hydrides of differing stereoselectivity, and also by two aluminium alkoxides in Meerwein–Ponndorf–Verley reactions. The products can be rationalised on the basis of recently proposed configurations for thujones and thujols. Convenient methods are described for the preparation of thujone, isothujone, thujol, neothujol, neoisothujol, and isothujol. A claim to prepare both thujones and thujols by base-promoted condensation of acetone could be substantiated.