Oxidation Of Allylic Alcohols Research Articles

DNA-Compatible Copper/TEMPO Oxidation for DNA-Encoded Libraries.

Aldehydes are important synthons for DNA-encoded library (DEL) construction, but the development of a DNA-compatible method for the oxidation of alcohols to aldehydes remains a significant challenge in the field of DEL chemistry. We report that a copper/TEMPO catalyst system enables the solution-phase DNA-compatible oxidation of DNA-linked primary activated alcohols to aldehydes. The semiaqueous, room-temperature reaction conditions afford oxidation of benzylic, heterobenzylic, and allylic alcohols in high yield, with DNA compatibility verified by mass spectrometry, qPCR, Sanger sequencing, and ligation assays. Subsequent transformations of the resulting aldehydes demonstrate the potential of this method for robust library diversification.

Disproportionation-Inspired Construction of Highly Functionalized Bicyclo[3.2.1]octanes.

The formation of one unavoidable byproduct in traditional disproportionation reactions limits their applications in synthesis. Inspired by convergent disproportionation, we develop an iodine-induced cyclization and oxidation of allylic alcohols to produce highly functionalized bicyclo[3.2.1]octanes through creation of six new bonds. Guided by the mechanism, we elaborated a variety of other bicyclo[3.2.1]octanes bearing distinct groups with presynthesized dienes and enones as the starting materials. This work provides a divergent access to bicyclo[3.2.1]octane frameworks.

Switchable Synthesis of Aldehydes and Carboxylic Acids from Alcohols by Platinum‐Catalysed Hydrogen Peroxide Oxidation Using Flow Reactors

AbstractSwitchable synthesis of aldehydes and carboxylic acids from alcohols by Pt‐catalysed H2O2 oxidation is performed for the first time using flow reactors. The use of an optimised amount of zero‐valent Pt black diluted with SiO2 catalyst demonstrates controlled H2O2 oxidation of allylic alcohols, benzyl alcohols, and aliphatic alcohols. From a probe reaction, Pt catalytic activity to produce a carboxylic acid from the corresponding alcohol improves depending on the temperature increasing from 40 to 90 °C. The set of reaction conditions about the combination of temperature and flow rate as a simple trigger works sensitively to divide the formation of aldehydes and carboxylic acids without tuning by additives.magnified image

Front Cover Picture: Aryl‐Alcohol‐Oxidase‐Mediated Synthesis of Piperonal and Other Valuable Aldehydes (Adv. Synth. Catal. 14/2022)

The front cover image illustrates the oxidation of primary aromatic and aliphatic allylic alcohols to valuable aldehydes catalyzed by a recombinant aryl-alcohol oxidase of Pleurotus eryngii P34. This versatile enzyme demonstrates high stability against the by-product of the reaction, H2O2, and in the presence of organic solvents. After reaction optimization, a space-time-yield of 9.5 g piperonal/l/h was achieved on a preparative scale. The produced aldehydes are of great interest as fragrances or building blocks in the synthesis of pharmaceuticals. Further details can be found in the Research Article by Urlacher and co-workers (N. Jankowski, K. Koschorreck, V. B. Urlacher, Adv. Synth. Catal. 2022, 364, XXXX–XXXX; DOI: 10.1002/adsc.202200381)

Pd-catalyzed selective oxidation of allyl alcohols to access enones and enals

Selective oxidation is quite important in synthesis. Here we report a Pd-catalyzed method to selectively oxidize allylic alcohols to enones and enals at room temperature. 27 compounds, including enones, and enals, have been obtained with moderate to excellent yields. Meanwhile, this approach proceeds well on a preparative scale giving a good yield. This work allows the efficient and selective oxidization of various allylic alcohols to access various enones and enals, even in the presence of benzylic alcohols. This procedure avoids the use of stoichiometric or superstoichiometric quantities of oxidant reagents such as MnO2 and uses free oxygen in the air as our green oxidant in the whole process.

One-pot, facile synthesis and fast separation of a UiO-66 composite by a metalloporphyrin using nanomagnetic materials for oxidation of olefins and allylic alcohols

One-pot facile synthesis of a new composite based on the incorporation of a metalloporphyrin within the UiO-66 metal–organic framework is reported.

β-MnO2 nanoparticles as heterogenous catalysts for aerobic oxidative transformation of alcohols to carbonyl compounds, nitriles, and amides

β-MnO2 nanoparticles exhibit high catalytic performance for the aerobic oxidation of various aromatic, allylic, and heteroaromatic alcohols and one-pot tandem oxidation of alcohols to nitriles and amides in the presence of NH3.

Pd-Catalyzed Selective Oxidation of Allyl Alcohols to Access Enones and Enals

Pd-Catalyzed Selective Oxidation of Allyl Alcohols to Access Enones and Enals

Triple-phase Boundary in Anion-Exchange Membrane Reactor Enables Selective Electrosynthesis of Aldehyde from Primary Alcohol.

Oxidation of primary alcohol to the corresponding aldehyde remains a significant challenge, even with the state-of-the-art chemistry. Here, a novel electrochemical system was developed for the exclusive production of aldehyde from primary alcohol using an anion-exchange membrane (AEM) reactor. Oxidation proceeded on a gold catalyst under basic conditions, which largely enhanced the reaction rate. Despite the basic nature around the reaction sites, the oxidation of primary alcohols exclusively yielded the corresponding aldehyde, which was attributed to the unique three-phase interfacial reaction sites in the AEM reactor. In addition to benzyl alcohol, the oxidation of allylic and aliphatic alcohols was also demonstrated. Comparison of constant potential electrolysis with the AEM reactor or a conventional batch-type cell revealed the crucial role of the triple-phase boundary for the selectivity of the oxidation of alcohol.

Palladium-doped hierarchical ZSM-5 for catalytic selective oxidation of allylic and benzylic alcohols

Hierarchical zeolites have the potential to provide a breakthrough in transport limitation, which hinders pristine microporous zeolites and thus may broaden their range of applications. We have explored the use of Pd-doped hierarchical ZSM-5 zeolites for aerobic selective oxidation (selox) of cinnamyl alcohol and benzyl alcohol to their corresponding aldehydes. Hierarchical ZSM-5 with differing acidity (H-form and Na-form) were employed and compared with two microporous ZSM-5 equivalents. Characterization of the four catalysts by X-ray diffraction, nitrogen porosimetry, NH3 temperature-programmed desorption, CO chemisorption, high-resolution scanning transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy allowed investigation of their porosity, acidity, as well as Pd active sites. The incorporation of complementary mesoporosity, within the hierarchical zeolites, enhances both active site dispersion and PdO active site generation. Likewise, alcohol conversion was also improved with the presence of secondary mesoporosity, while strong Brønsted acidity, present solely within the H-form systems, negatively impacted overall selectivity through undesirable self-etherification. Therefore, tuning support porosity and acidity alongside active site dispersion is paramount for optimal aldehyde production.

Selective aerobic oxidation of benzylic and allylic alcohols catalyzed by Cu(OAc)2/TEMPO/Et2NH

Selective oxidation of benzylic and allylic alcohols to their corresponding aldehyde/ketone derivative without affecting saturated alcohols is still a challenging endeavor in organic synthesis. Various metal complexes, especially the copper complexes in the presence of TEMPO are being used very often for such transformations under aerobic conditions, but they are not selective to allylic and benzylic alcohols. The use of copper salt for oxidation of alcohols in the absence of a ligand are very scarcely studied except for the one catalyzed by CuCl/TEMPO where chloride inhibition and lack of selective oxidation have been noted upon use of CuCl 2 . Herein we report a Cu(OAc) 2 catalyzed and TEMPO mediated selective aerobic oxidation of benzylic and allylic alcohols to aldehyde/ketone in the presence of Et 2 NH. The method avoids pre-synthesis of the catalyst as in the case of Cu(II)/(I) complexes/TEMPO catalyzed oxidation reactions, requires low catalyst loading, employs cheaper copper salt, and gives excellent selectivity for oxidation of benzylic and allylic alcohols.

A new catalytic approach for aerobic oxidation of primary alcohols based on a Copper(I)-thiophene carbaldimines

• Novel in situ copper(I) iodide schiff base catalysts. • High activity for the aerobic oxidation of benzylic, allylic and aliphatic alcohols. • Quantitative yields for benzaldehyde in 3 h with a catalyst loading of 2.5 mol%. • Diol oxidation to the corresponding lactol. We report here novel Cu(I) thiophene carbaldimine catalysts for the selective aerobic oxidation of primary alcohols to their corresponding aldehydes and various diols to lactones or lactols. In the presence of the in situ generated Cu(I) species, a persistent radical (2,2,6,6-tetramethylpiperdine-N-oxyl (TEMPO)) and N-methylimidazole (NMI) as an auxiliary ligand, the reaction proceeds under aerobic conditions and at ambient temperature. Especially the catalytic system of 1-(thiophen-2-yl)-N-(4-(trifluoromethoxy)phenyl)methanimine (ligand L2 ) with copper(I)-iodide showed high reactivity for all kind of alcohols (benzylic, allylic and aliphatic). In the case of benzyl alcohol even 2.5 mol% of copper loading gave quantitative yield. Beside high activity under aerobic conditions, the catalysts ability to oxidize 1,5-pentadiol to the corresponding lactol (86% in 4 h) and N-phenyldiethanolamine to the corresponding morpholine derivate lactol (86% in 24 h) is particularly noteworthy.

Expansion of Substrate Scope for Nitroxyl Radical/Copper-Catalyzed Aerobic Oxidation of Primary Alcohols: A Guideline for Catalyst Selection.

Four distinctive sets of optimum nitroxyl radical/copper salt/additive catalyst combinations have been identified for accommodating the aerobic oxidation of various types of primary alcohols to their corresponding aldehydes. Interestingly, less nucleophilic catalysts exhibited higher catalytic activities for the oxidation of particular primary allylic and propargylic alcohols to give α,β-unsaturated aldehydes that function as competent Michael acceptors. The optimum conditions identified herein were successful in the oxidation of various types of primary alcohols, including unprotected amino alcohols and divalent-sulfur-containing alcohols in good-to-high yields. Moreover, N-protected alaninol, an inefficient substrate in the nitroxyl radical/copper-catalyzed aerobic oxidation, was oxidized in good yield. On the basis of the optimization results, a guideline for catalyst selection has been established.

Asymmetric total syntheses of (–)-ar-turmerone, (–)-dihydro-ar-turmerone, (–)-ar-dehydrocurcumene, and (–)-ar-himachalene via a key allylic oxidative rearrangement

A Nature inspired strategy to oxidized aromatic bisabolanes has been envision from naturally occurring 2-methyl-6-(4′-methylphenyl)-3-hepten-2-ol (2a). The key methodology utilized in this synthesis is the allylic oxidative rearrangement following a [3,3]-sigmatropic rearrangement (Dauben oxidation) of tertiary allylic alcohol of natural product 2a. The enantioselectivity of 2a has been introduced via a Rh(I)-(S)-BINAP catalyzed p-tolylboronic acid addition onto E-ethylcrotonate. Thus, the total syntheses of (–)-ar-turmerone (1a), (-)-dihydro-ar-turmerone (1b) and (-)-ar-himachalene (3) has been achieved only in 6–7 steps.

Reaction Pathway Discrimination in Alkene Oxidation Reactions by Designed Ti‐Siloxy‐Polyoxometalates

AbstractTitanium complexes of silanol functionalized polyoxometalates (THA)3[SbW9O33(RSiO)3Ti(OiPr)] (Ti‐SiloxPOMs) catalyze alkene oxidation with tert‐butyl hydrogen peroxide (TBHP). However catalytic activity and product distribution in the oxidation of allylic alcohols are shown to depend on the steric surrounding generated by the SiloxPOM (R=tBu, iPr, nPr). Combined experimental and computational studies clarify how steric repulsions between the oxidant (tBu group) and the surrounding SiloxPOM govern the reaction pathways leading either to oxidation of the alcohol function (R=tBu) or to alkene epoxidation (R=nPr). Moreover, another consequence of this steric repulsive interactions is that outer‐sphere mechanisms become competitive with the inner‐sphere ones (coordination of allylic alcohol), whether for the oxidative dehydrogenation reaction or for the epoxidation reaction. In the case of unfunctionalized olefins (linear and cyclic), we show that reducing the bulkiness surrounding the active site leads to higher conversion to epoxide, emphasizing that these Ti‐SiloxPOMs may behave as structural and functional models for metal single‐site in Ti‐Silicates.

Decoration of Ni/C with Small Amounts of Pd and Au for Allyl Alcohol Oxidation

The decoration of the surface of Ni nanoparticles supported on carbon black with Pd and Au and the electrooxidation of allyl alcohol on the Au/Pd/Ni/C catalysts in alkaline solution have been investigated. The decoration of Ni/C is performed by the electrochemical deposition of a small amount of Pd and then Au on Ni/C, and the Aux/Pdy/Ni100/C catalysts with the (x+y):100 atomic ratios of less then 4.5 (0.2 < x < 1.2 and 0.6 < y < 3.1) are prepared. Characterizations of Au/Pd/Ni/C reveal a uniform dispersion of the metal nanoparticles on carbon black and a low coverage of Au and Pd on the Ni nanoparticle surface. Au/Pd/Ni/C behaves more similar to Pd/C than Au/C in allyl alcohol oxidation, and the catalytic activity of Au/Pd/Ni/C depends on the amounts of Pd and Au, with Au0.9/Pd2.2/Ni100/C exhibiting the highest activity. Besides Pd and Au, the Ni nanoparticles also play important roles in the activity of Au/Pd/Ni/C, although Ni itself has no catalytic activity. The lack of any one of Pd, Au and Ni leads to low catalytic activity, indicating the synergy among the three metals. The result is helpful for preparing ternary electrocatalysts by the surface decoration.

Facile bile salt-induced synthesis of porous MnO2 nanoflowers: applications in dye removal and oxidation

MnO2 is an important functional oxide with wide applications such as in the oxidation of benzylic and allylic alcohols, as an electrode material for supercapacitors, in dyes removal etc. Herein, we demonstrate a simple, bile-salt induced synthesis of porous MnO2 at neutral pH from potassium permanganate. By tuning the reaction conditions we obtained porous δ-MnO2 with high surface area which adsorbed cationic organic dyes with high efficiency. Because of its high reactivity, we also observed higher yields in standard oxidation reactions as compared to commercial MnO2. The outstanding dye adsorption and oxidation abilities coupled with the simple method of preparation can make this material useful for practical applications such as for wastewater treatment.

An RCM‐Based Total Synthesis of the Antibiotic Disciformycin B

The total synthesis of the potent new antibiotic disciformycin B (2) is described, which shows significant activity against methicillin- and vancomycin-resistant Staphylococcus aureus (MRSA/VRSA) strains. The synthetic route is based on macrocyclization of a tetraene substrate to the 12-membered macrolactone core by ring-closing olefin metathesis (RCM). Although macrocyclization was accompanied by concomitant cyclopentene formation by an alternative RCM pathway, conditions were established to give the macrocycle as the major product. Key steps in the construction of the RCM substrate include a highly efficient Evans syn-aldol reaction, the asymmetric Brown allylation of angelic aldehyde, and the stereoselective Zn(BH4 )2 -mediated 1,2-reduction of an enone. The synthesis was completed by late-stage dehydrative glycosylation to introduce the d-arabinofuranosyl moiety and final chemoselective allylic alcohol oxidation.

Gold nanoparticles onto cerium oxycarbonate as highly efficient catalyst for aerobic allyl alcohol oxidation

Au nanoparticles, generated by the metal vapor synthesis technique, were supported onto cerium oxycarbonate monohydrate (Ce2O(CO3)2·H2O) giving Au@Ce2O(CO3)2·H2O. The obtained heterogeneous catalyst was used in the aerobic allyl alcohol oxidation reaction performed in toluene, showing a notably higher catalytic substrate conversion and isomerization activity compared to Au onto ceria, which is the reference catalyst for this type of catalysis. Results originating from catalytic recycling experiments and PXRD, HRTEM and XPS measurements carried out on recovered Au@Ce2O(CO3)2·H2O, confirmed the stability of the catalyst under aerobic oxidation reaction conditions and hence its recyclability, without the need of a regeneration step.

The Reims Journey Towards Discovery and Understanding of Pd-Catalyzed Oxidations

This review recounts the development by the authors of the Pd-catalyzed procedures devoted to various kinds of oxidation. Starting with reactions assisted with UV light, the research has explored reactions under light-free conditions: allylic oxidation, alcohol oxidation, etherification, Wacker oxidation and dehydrogenations with, always, accompanying efforts towards mechanism determination.