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In this study, Na-ZrO2 was prepared from two types of ZrO2 as solid base catalyst and the catalytic activity, selectivity, and mechanism of Na-ZrO2 for base catalyzed reactions in subcritical water were elucidated using aldol condensation between acetophenone and benzaldehyde as a model reaction. Based on the different selectivity for Cannizzaro reaction of benzaldehyde, a side reaction accompanied with the aldol condensation, two plausible mechanisms were proposed. One was that the doped Na2O could directly act as a base, deprotonating the acetophenone for catalyzing aldol condensation, and the other was that the doped Na2O could dissociate the water to provide OH− for catalyzing both aldol condensation and Cannizzaro reaction. The dominant mechanism varied depending on the nature of the ZrO2 support. The effect of the amount of subcritical water was also examined, showing that as reducing the loading of water, the yield of byproduct from the Cannizzaro reaction decreased due to the lower amount of dissociated OH−. On the other hand, the presence of water adversely affected the reaction equilibrium, but meanwhile sufficient water in the system also prevented the carbonization of organics and polymerization reaction on the catalyst surface, favoring for a ring balance.

The Cannizzaro reaction has emerged as a versatile synthetic tool for the construction of functionalized molecules. Dating back to the 19th century, this reaction, though initially used for the synthesis of an alcohol and acid functionality from aldehydes, has henceforth proven useful to generate diverse molecular entities using both intermolecular and intramolecular synthetic strategies. Immense applications in the synthesis of hydroxy acids and esters, heterocycles, fused carbocycles, natural products, and others with broad substrate scope have raised profound interest from methodological and synthetic standpoints. The ongoing development of reagents, solvents, and technologies for the Cannizzaro reaction reflects the broader trend in organic synthesis towards more sustainable and efficient practices. The focus of this review is to highlight some recent advances in synthetic strategies and applications of the Cannizzaro reaction towards the synthesis of potentially useful molecules.

A tandem Cu‐catalyzed oxidation‐intramolecular Cannizzaro reaction leading to bioactive α‐hydroxyesters from α‐hydroxyketones is reported. The process uses oxygen as a sole oxidant to achieve the formation of glyoxals, which are efficiently converted in situ to important α‐hydroxyesters. The mechanistic insights are provided by isotopic labeling and supported by DFT calculations. The transformation proved a robust synthetic tool to achieve the synthesis of human metabolites and hydroxyl esters of various biologically active steroid derivatives. [ABSTRACT FROM AUTHOR]

A simple synthesis of a novel fungicide mandipropamid has been achieved in six steps, with an overall yield of 43%. Synthesis has been carried out from commercially available starting materials, 4-chloroacetophenone and vanillin. The key steps involved in the synthesis are Cannizzaro and Henry reactions, amide bond formation and O-propargylation. [ABSTRACT FROM AUTHOR]

A simple and efficient protecting group free synthesis of a relatively new fungicide Mandipropamid has been achieved in five steps, with an excellent overall yield. The synthesis started from commercially available starting materials like vanillin and p-chloroacetophenone. The key steps involved in the synthesis are the Henry and Cannizzaro reactions, as well as amide formation through a carboxylic acid-amine coupling step. [ABSTRACT FROM AUTHOR]

Aldol condensation reactions between furfural and various ketones were studied in a flow reactor at 373 K and 100 psi for application to upgrading of furfural. Specific rates for the reaction of acetone and furfural were measured on MgAl2O4, Al2O3, CaO/MgAl2O4 and MgO/MgAl2O4 and found to be highest on CaO/MgAl2O4. While the presence of CO2 and H2O did not affect the stability of the CaO/MgAl2O4 catalyst, the catalyst deactivated over a period of a few hours due to the production of 2-furoic acid formed by the Cannizzaro reaction. While aldol condensation rates between furfural and either 2-pentanone and decanal approached that of acetone, rates for 4-heptanone and 2,5-heptanedione were significantly lower because the α-hydrogens of the carbonyl compounds are less easily attacked in these molecules. The selectivity to aldol products is affected by the relative rates of the aldol-condensation and the Cannizzaro reactions. Possible strategies for maximizing production of the aldol products with larger ketones are discussed. [ABSTRACT FROM AUTHOR]

The reaction of 3,5-dimethyl- and 5-methyl-3-(2-propyl)tetrahydro-4H-thiopyran-4-ones with formaldehyde without or in the presence of 0.1–0.5 equiv. sodium hydroxide produces 3,5-dialkyl-3-(hydroxymethyl)tetrahydro-4H-thiopyran-4-ones. 3,5-Dimethyltetrahydro-4H-thiopyran-4-one converted into 3,5-bis(hydroxymethyl)tetrahydro-2H-thiopyran-4-ol when the amount of base to 1 equiv increase. Under similar conditions 5-methyl-3-(2-propyl)tetrahydro-4H-thiopyran-4-one form 3-hydroxymethyltetrahydro-2H-thiopyran-4-ol, which cyclization to 7-oxa-3-thiabicyclo[4.2.0]octane. [ABSTRACT FROM AUTHOR]

Pine bark, a natural and renewable forest residue, was modified using a simple interfacial solid-phase chemical method to design a highly chemically reactive additive for urea-formaldehyde (UF) resin. The modification introduced carbonyl groups onto the bark surface during the glyoxal reaction at the bark-solid interface. Thermal properties, including curing temperatures, of UF, UFB, and UFGB were evaluated using DSC and DMA. Glyoxal modification of bark significantly influenced these properties, facilitating the crosslinking and curing of adhesives. Notably, plywood bonded with UFGB resin released approximately half as much formaldehyde (52.89 % less) compared to plywood bonded with UF resin, reducing from 1.38 to 0.65 mg/L. Additionally, the wet shear strength of plywood increased by 197.3 %, from 0.37 MPa to 1.10 MPa, exceeding the minimum requirement (0.7 MPa) defined by the China national standard (GB/T 17657–2013). The study presents a compelling case for the utilization of glyoxal-modified pine bark as a filler in UF adhesive for plywood manufacturing. The demonstrated improvements in plywood properties and formaldehyde emissions, along with the environmentally friendly nature of the approach, make it a promising avenue for sustainable plywood production. Further investigations into the underlying mechanisms and long-term performance are encouraged to solidify the potential of this technology. [Display omitted] • Reduced formaldehyde emissions: Plywood bonded with a UF resin containing glyoxal-modified pine bark as a reactive additive released nearly 53 % less formaldehyde , a major health concern. • Enhanced strength: The wet shear strength of the plywood increased by almost 200 % , exceeding national standards. • Sustainable approach: Utilizing a natural waste product and a simple modification process makes this method environmentally friendly. • Cost-effective: The modified bark powder can be easily incorporated into existing production lines, minimizing additional costs. [ABSTRACT FROM AUTHOR]

In this research, new ferrocenylmethylesters were synthesized according to esterification reaction. To reach this purpose, direct and indirect esterification methods were used. Indirect method included Cannizzaro reaction of new alkylferrocenecarboxaldehydes result in production of alkylferrocenecarboxylic acids and alkyl(hydroxymethyl)ferrocene derivatives. Finally, a variety of known procedures were used for converting the new alkylferrocenecarboxylic acids to the corresponding esters. The oxidative esterification reaction was accomplished using K2CO3/I2 as oxidant in the direct method. The advantages of this method are one-pot and single-step reaction and remarkably high total yield of this procedure. The chemical structures were confirmed with FT-IR, 1H NMR, 13C NMR and MASS spectroscopy as well as CHN analysis. Electrochemical behavior of synthesized compounds was studied by cyclic voltammetry, and the relationship between the peak currents and the square root of the scan rate showed that the redox process is diffusion-limited. [ABSTRACT FROM AUTHOR]

The Cannizzaro reaction of benzaldehyde is a representative experiment in organic chemistry teaching experiment. This experiment is highly comprehensive, since it involves with many basic techniques and complicated operations. Students can get the corresponding training of the preparation and purification of liquid and solids respectively. Being a mature and classic teaching experiment, the Cannizzaro reaction of benzaldehyde is always used as the final operation test of organic chemistry experiment. However, some new problems and situations were founded when the experiment was carried out repeatedly. In order to make the experiment more perfect and accurate, Cannizzaro reaction of benzaldehyde was further studied. On the basis of our previous study results, this essay attempted to further discuss and provide solutions to some new problems arising from the students ' experiment, such as: reaction temperature, the concentration of sodium hydroxide, the amount of solvent for recrystallization and the dehydration of benzyl alcohol, etc. The result of our study not only enhances the controllability of the Cannizzaro reaction of benzaldehyde, but also is very useful to improve the teaching quality of organic chemistry experiment, at the same time, it is contributed to accumulating faculties teaching experience. In addition, through addressing the aforementioned problems, it is helpful to improve the students ' skills of analyzing and solving problems as well as the their awareness of innovation. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Aqueous‐phase conversion of glyceraldehyde to lactic acid was investigated over Nb2O5, TiO2, ZrO2 and SnO2 in a fixed‐bed up‐flow reactor. Special attention was given to the catalysts acidity regarding the type, amount, strength and tolerance to water of surface acid sites. These sites were assessed by infrared spectroscopy of pyridine adsorbed on dehydrated and hydrated catalysts as well as by isopropanol decomposition. It was found that Nb2O5 and TiO2 have the highest fraction of water‐tolerant Lewis acid sites (40 and 47 %), while only 6 % was estimated for ZrO2. No relevant Lewis acidity was observed on SnO2, but it was noticed the presence of strong base sites. The transformation of glyceraldehyde into lactic acid proceeded via a cascade reaction in which glyceraldehyde is firstly dehydrated to pyruvaldehyde, followed by its rearrangement to lactic acid with the addition of a water molecule. The dehydration step occurs on Brønsted acid sites and/or on water‐tolerant Lewis acid sites. These latter sites also determine the selectivity to lactic acid. Strong base sites promote glyceraldehyde fragmentation leading to formaldehyde with high selectivity. [ABSTRACT FROM AUTHOR]

Abstract Several aldehydes undergo disproportionation into corresponding acids and alcohols (Cannizzaro reaction) over calcined hydrotalcite, magnesium aluminum layered double hydroxide (LDH), in water. The reactions are slow and ~10% conversions were achieved after stirring for 24 h at room temperature. The mixed metal oxide obtained on calcination of the LDH gets hydrated to a meixnerite-type phase, which provides the necessary basicity for the Cannizzaro reaction. The calcination temperature of LDH, if it is above the decarbonation temperature, has no appreciable effect on the outcome of the reaction. Highlights • LDH-derived mixed metal oxide catalyzes Cannizzaro reactions of aldehydes. • Reactions are slow, and the yields are low. • Calcination temperature has no effect on the catalysis. • The products get separated – the carboxylic acid gets intercalated in the regenerated LDH. [ABSTRACT FROM AUTHOR]

While formaldehyde (HCHO) was likely generated in Earth's prebiotic atmosphere by ultraviolet light, electrical discharge, and/or volcano-created lightning, HCHO could not have accumulated in substantial amounts in prebiotic environments, including those needed for prebiotic processes that generate nucleosidic carbohydrates. HCHO at high concentrations in alkaline solutions self-reacts in the Cannizzaro reaction to give methanol and formate, neither having prebiotic value. Here, we explore the possibility that volcanic sulfur dioxide (SO2) might have generated a reservoir for Hadean HCHO by a reversible reaction with HCHO to give hydroxymethanesulfonate (HMS). We show that salts of HMS are stable as solids at 90°C and do not react with themselves in solution, even at high (>8 M) concentrations. This makes them effective stores of HCHO, since the reverse reaction slowly delivers HCHO back into an environment where it can participate in prebiotically useful reactions. Specifically, we show that in alkaline borate solutions, HCHO derived from HMS allows formation of borate-stabilized carbohydrates as effectively as free HCHO, without losing material to Cannizzaro products. Further, we show that SO2 can perform similar roles for glycolaldehyde and glyceraldehyde, two intrinsically unstable carbohydrates that are needed by various models as precursors for RNA building blocks. Zircons from the Hadean show that the Hadean mantle likely provided volcanic SO2 at rates at least as great as the rates of atmospheric HCHO generation, making the formation of Hadean HMS essentially unavoidable. Thus, hydroxymethylsulfonate adducts of formaldehyde, glycolaldehyde, and glyceraldehyde, including the less soluble barium, strontium, and calcium salts, are likely candidates for prebiotically useful organic minerals on early Earth. [ABSTRACT FROM AUTHOR]

Sugars are essential for the formation of genetic elements such as RNA and as an energy/food source. Thus, the formose reaction, which autocatalytically generates a multitude of sugars from formaldehyde, has been viewed as a potentially important prebiotic source of biomolecules at the origins of life. When analyzing our formose solutions we find that many of the chemical species are simple carboxylic acids, including α-hydroxy acids, associated with metabolism. In this work we posit that the study of the formose reaction, under alkaline conditions and moderate hydrothermal temperatures, should not be solely focused on sugars for genetic materials, but should focus on the origins of metabolism (via metabolic molecules) as well.

We developed an on-packaging colorimetric sensor label that can detect the aldehyde emission of apples based on Methyl Red. The sensor label was constructed using printable inks on paper medium and relied on the change in basicity caused by the nucleophilic addition reaction between aldehyde and hydroxide via the Cannizzaro reaction. The sensor can be used to detect aldehyde in solution and vapor. Sensitivity and stability toward changes in humidity were achieved by altering the concentration of OH − . Under exposure to ripening apples, the label changed color from yellow to orange, and then to red. The degree of ripeness was estimated by a sensory test and texture analysis. The color change of sensor label had showed a similar tendency to the changes in the parameters of the sensory test, soluble solid content, and hardness. Therefore, the sensor label can be used for real time on-package ripeness monitoring of apples during their shelf life. [ABSTRACT FROM AUTHOR]

[Display omitted] • Brønsted acid sites are not active on aqueous-phase conversion of pyruvaldehyde. • TiO 2 , ZrO 2 and Nb 2 O 5 water-tolerant Lewis acid sites are responsible for activity. • Nb 2 O 5 is the most active and stable catalyst. • ZnO fastly deactivated due to the formation of amorphous carbonaceous materials. The eventual role played by Brønsted and Lewis acid sites on pyruvaldehyde Cannizzaro reaction to lactic acid was investigated in a flow reactor using different catalysts bearing different acidity. It was shown that Lewis acid sites on heterogeneous catalysts are crucial for the reaction while Brønsted sites play no role at all. The results revealed that catalytic activity is indeed directly related to catalyst acidity. TiO 2 , ZrO 2 and Nb 2 O 5 were the most promising catalysts and their activity was related to their water-tolerant Lewis acid sites. Nb 2 O 5 was shown to be the most active and stable catalyst while ZnO underwent a fast deactivation process ascribed to the formation of amorphous carbonaceous materials as revealed by TG and laser Raman spectroscopy. [ABSTRACT FROM AUTHOR]

The study describes the synthesis of new α,α-disubstituted β-amino acid (β2,2-Caa) and attempts the synthesis of peptides from it. The β2,2-Caa was prepared from D-(+)-mannose, using crossed aldol and Cannizzaro reactions. [ABSTRACT FROM AUTHOR]

The Cannizzaro reaction of pyruvaldehyde to lactic acid is investigated in a flow reactor with ZrO2 catalysts with different structures and acid-base properties. The results show that a difference in the crystalline structures of two ZrO2 polymorphs strongly affects the conversion of pyruvaldehyde. The monoclinic phase of zirconia is the most active for this reaction. A good correlation is observed between the reaction rate and the concentration of Lewis acid sites of sufficient strength, which shows that these sites play a major role in the reaction. A reaction mechanism is proposed involving coordinatively unsaturated Zr4+ cations as sites for activating pyruvaldehyde molecules, whereas Zr4+-O2- pairs generate terminal OH groups through water dissociation. [ABSTRACT FROM AUTHOR]

A novel reaction involving in situ redox conversion of glyoxylate esters to glycine is described. Simple starting materials and mild conditions for the synthesis of glycine derivatives probably indicate a pathway towards prebiotic chemistry. This proceeds analogous to Cannizzaro reaction involving ammonia therefore it can be termed as intramolecular Aza-Cannizzaro type reaction. This reaction is examined in detail with an aid of computational analysis to corroborate the proposed mechanism. [ABSTRACT FROM AUTHOR]

Aldol condensation in presence of reconstructed hydrotalcites as basic catalysts is well documented and attracts an increased attention because it allows producing complex molecules starting from relatively simpler ones. Nevertheless, more studies are necessary for the better understanding of preparation factors that affect the physico-chemical properties of these materials and their catalytic performance. This work considers the effect of the duration of the liquid-phase rehydration of Mg-Al mixed oxide as well as the drying duration of prepared samples on their physico-chemical properties and performance in aldol condensation of furfural and acetone. The properties of all materials were investigated by XRD, TGA, TGA-MS, SEM and DRIFT. Experiments on aldol condensation of furfural and acetone were performed by using a stirred batch reactor at T = 25 °C with Ac:F = 5 molar ratio. The characterization of the prepared materials showed that the recovery of HTC structure occurred within a few seconds of the contact between Mg-Al mixed oxide with liquid water. The content of functional species in all reconstituted HTCs was nearly constant and independent on preparation conditions while the amount of physisorbed water in the prepared samples decreased with increasing drying time. The calcination of as-prepared HTC followed by the subsequent rehydration of Mg-Al mixed oxide resulted in the replacement of >90% carbonate groups on hydroxyls which are Brønsted basic sites. Consequently, the activity of the reconstructed HTCs in aldol condensation of furfural and acetone was significantly higher compared to Mg-Al mixed oxide. The catalytic performance of rehydrated materials was almost independent on rehydration time while furfural conversion decreased if carrying out the reaction in an aqueous medium with increased water content. On the other hand, properly dried reconstructed HTC with the absence of physisorbed water also exhibited a very low activity in the reaction. The effect of Cannizzaro reaction as a simultaneous process with aldol condensation on the composition of reaction products was also considered. The obtained results may be useful for optimizing the preparation conditions of reconstructed HTC as a basic catalyst as well as for evaluating their performance during long-term catalytic tests. [ABSTRACT FROM AUTHOR]

Cannizzaro reaction of various aryl aldehydes employing solvent free grindstone technique using solid sodium hydroxide was examined and obtained excellent yields (94–99%) with 97–100% conversion rate.

The formation of low molecular carboxylic and hydroxycarboxylic acids as well as sugar and deoxysugar acids from monosaccharides (D-glucose, D-fructose, D-arabinose, DL-glyceraldehyde, and 1,3-dihydroxyacetone) was studied in three different model systems: aqueous and alkaline solutions of potassium peroxodisulfate (K2S2O8), and sodium hydroxide solution. In total, 3 low molecular carboxylic acids (formic, acetic and propionic), 24 hydroxycarboxylic acids, and 12 corresponding lactones were identified and quantified by GC/MS. Formic, acetic, and propionic acids were isolated by extraction with diethyl ether and directly analysed by GC/MS; hydroxycarboxylic acids and their lactones were monitored as their trimethylsilylated derivatives using the same method. Formic, acetic, L-lactic, glycollic, DL-2,4-dihydroxybutanoic acids and aldonic acids derived from the parent sugars were the most abundant compounds in all model systems. Within the models investigated, the yield of carboxylic acids and hydroxycarboxylic acids (together with their lactones) ranged between 9.3-22.2% (n/n) and between 3.6-116.9% (n/n), respectively. The amount of acids was significantly lower in aqueous solutions of K2S2O8 than in the alkaline solutions. The data obtained indicate that lower carboxylic acids are formed by both subsequent reactions (oxidation and/or intramolecular Cannizzaro reaction) of the sugar fragmentation products and direct decomposition of some intermediates such as uloses or hydroperoxides derived from the parent sugars. The acids possessing the original sugar skeleton are formed as a result of sugar oxidation or benzilic acid type rearrangement of deoxyuloses. Lower acids may also be formed by a recombination of free radicals.

Monocyclic analog of neuroexcitatory neodysiherbaine has been designed and stereoselectively synthesized in 0.40% yield over total 24 steps starting from d -ribose, by employing domino aldol-Cannizzaro reaction and stereoselective aldol reaction for construction of two quaternary carbon stereogenic centers at C4 and C6 positions, respectively. The hyperactivity of neodysiherbaine in mice was found to deteriorate in the novel analog, upon intracerebroventricular injection. [ABSTRACT FROM AUTHOR]

Mg-Al mixed oxides and reconstructed hydrotalcites prepared from mixed oxides by rehydration attract much attention as solid basic catalysts for organic reactions, such as aldol condensation. Therefore, the understanding of parameters that govern their catalytic performance is of great importance. Cannizzaro reaction in the presence of mixed oxide and reconstructed HTC as basic catalysts was used as a model reaction to characterize both catalytic systems and to understand their behavior in aldol condensation. The performance of the samples was investigated in the conversion of aqueous furfural mixture using stirred batch reactor operating at T = 50 °C. The properties of both initial samples and catalysts after reaction were studied by different physico-chemical methods, such as XRD, DRIFT and TGA. It was shown that both mixed oxide and reconstructed HTC possessed poor activity in the conversion of dried furfural proving the importance of water presence for the reaction to take place. Addition of water to the reaction mixture resulted in growth of the yield of both furfuryl alcohol and furoyl furoate as reaction products. Furoic acid was not identified by GC analysis, but the interaction of the acid with the basic sites of catalysts was confirmed by DRIFT and TGA analyses indicating that at optimum reaction conditions, most of the basic sites were involved in the formation of furoate species. The formation of the surface furoate species influenced the behavior of the basic catalysts in aldol condensation of furfural and acetone. It allows concluding that the occurrence of Cannizzaro reaction should be taken into account when considering the behavior of basic catalysts in organic reactions with furfural as a reactant. [ABSTRACT FROM AUTHOR]

Aqueous polyurethane dispersions (APUDs) are commodity synthetic polymers and have a broad range of well-known applications, nevertheless their possible use as a green catalyst or ionic solvent is yet unknown. Here, we demonstrate how a polyurethane dispersion facilitates the progress of the Cannizzaro reaction under very mild alkaline conditions. We introduce anionic polyurethane nanomicelles as an expeditious green polymer ionic solvent for the Cannizzaro reaction. The reusable and novel eco-friendly polymer solvent, excellent yields of the products, low reaction times and low reaction temperatures are the main advantages of this reaction. [ABSTRACT FROM AUTHOR]

An intramolecular Cannizzaro-type hydride transfer to an in situ prepared allene enables the synthesis of ortho-fused 4-substituted cycloocta-2,5-dien-1-ones with unprecedented technical ease for an eight-ring carboannulation. Various derivatives could be obtained from commercially available (hetero)aryl aldehydes, trimethylsilylacetylene, and simple propargyl chlorides in good yields. [ABSTRACT FROM AUTHOR]

An environmentally benign catalyst, the N,N′-dioxide–FeCl3 complex, has been developed for the asymmetric intramolecular Cannizzaro reaction. Aryl and alkyl glyoxal monohydrates were applied to obtain α-hydroxy acid esters with excellent results. Deuterium-label and control experiments shed light on the reaction mechanism. [ABSTRACT FROM AUTHOR]

Copyright of Avances en Ciencias e Ingeniería is the property of Avances en Ciencias e Ingenieria and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Herein, we demonstrate that hollow Pd nanotubes could serve as a highly efficient and convenient catalyst for inhibiting Cannizzaro reaction and facilitating hydrogen generation from alkaline formaldehyde solution at room temperature. Moreover, this hollow nanostructure exhibits much higher capability and stability for hydrogen production than conventional Pd nanoparticles. By further optimizing the reaction parameters such as reaction temperature, formaldehyde concentrations, and NaOH concentrations, the hydrogen generation rates could be further increased. Moreover, except for formaldehyde, other aldehydes, including acetaldehyde, propanal, and benaldehyde, could also produce hydrogen with high efficiencies. Owing to its high efficiency at room temperature, this Pd nanotube based hydrogen generation reaction may serve as an alternate hydrogen supply candidate. [ABSTRACT FROM AUTHOR]

A total synthesis of 6-O-benzoylzeylenol from diacetone glucose is described. The key steps were a crossed aldol-Cannizzaro reaction to create a quaternary carbon stereocenter, and cyclization through ring closure metathesis (RCM). Of the four stereogenic centers, two were derived from diacetone glucose, the quaternary stereocenter was created by means of the crossed aldol-Cannizzaro reaction, and the fourth stereogenic center was produced by a Sharpless asymmetric epoxidation. Finally, cyclization through RCM and deprotection by removal of a benzyl group with titanium( IV) chloride gave the target molecule. [ABSTRACT FROM AUTHOR]

The mechanism of the disproportionation of 2,5-diethyl-3,4-dihydro-2 H-pyran-2-carbaldehyde in the Cannizzaro reaction in ethanol was studied by quantum-chemical modeling. The geometry was optimized by the semiempirical RM1 method in the unrestricted Hartree-Fock approximation, and the heats of formation of the reagents and transitional states were calculated. Two possible hydride transfer reaction paths are presented: through the formation of a transition state with one-center interaction or through a transition state with two-center interaction. The theoretically calculated values of the thermodynamic parameters agree with the experimental values and confirm the hydride transfer mechanism. [ABSTRACT FROM AUTHOR]

Three biomimetic iron(II) α-hydroxy acid complexes, [(TpP2h)FeII(mandelate)(H2O)] (1), [(TpP2h)FeII(benzilate)] (2), and [(TpP2h)FeII(HMP)] (3), together with two iron(II) α-methoxy acid complexes, [(TpP2h)FeII(MPA)] (4) and [(TpP2h)FeII(MMP)] (5) (where HMP = 2-hydroxy-2-methylpropanoate, MPA = 2-methoxy-2-phenylacetate, and MMP = 2-methoxy-2-methylpropanoate), of a facial tridentate ligand TpP2h [where TpP2h = hydrotris(3,5-diphenylpyrazole-1-yl)borate] were isolated and characterized to study the mechanism of dioxygen activation at the iron(II) centers. Single-crystal X-ray structural analyses of 1, 2, and 5 were performed to assess the binding mode of an α-hydroxy/methoxy acid anion to the iron(II) center. While the iron(II) α-methoxy acid complexes are unreactive toward dioxygen, the iron(II) α-hydroxy acid complexes undergo oxidative decarboxylation, implying the importance of the hydroxyl group in the activation of dioxygen. In the reaction with dioxygen, the iron(II) α-hydroxy acid complexes form iron(III) phenolate complexes of a modified ligand (TpP2h*), where the ortho position of one of the phenyl rings of TpP2h gets hydroxylated. The iron(II) mandelate complex (1), upon decarboxylation of mandelate, affords a mixture of benzaldehyde (67%), benzoic acid (20%), and benzyl alcohol (10%). On the other hand, complexes 2 and 3 react with dioxygen to form benzophenone and acetone, respectively. The intramolecular ligand hydroxylation gets inhibited in the presence of external intercepting agents. Reactions of 1 and 2 with dioxygen in the presence of an excess amount of alkenes result in the formation of the corresponding cis-diols in good yield. The incorporation of both oxygen atoms of dioxygen into the diol products is confirmed by 18O-labeling studies. On the basis of reactivity and mechanistic studies, the generation of a nucleophilic iron-oxygen intermediate upon decarboxylation of the coordinated α-hydroxy acids is proposed as the active oxidant. The novel iron-oxygen intermediate oxidizes various substrates like sulfide, fluorene, toluene, ethylbenzene, and benzaldehyde. The oxidant oxidizes benzaldehyde to benzoic acid and also participates in the Cannizzaro reaction. [ABSTRACT FROM AUTHOR]