Cyclic Alcohols Research Articles

Synergistic use of photocatalysis and convergent paired electrolysis for nickel-catalyzed arylation of cyclic alcohols

The merging of transition metal catalysis with electrochemistry has become a powerful tool for organic synthesis because catalysts can govern the reactivity and selectivity. However, coupling catalysts with alkyl radical species generated by anodic oxidation remains challenging because of electrode passivation, dimerization, and overoxidation. In this study, we developed convergent paired electrolysis for the coupling of nickel catalysts with alkyl radicals derived from photoinduced ligand-to-metal charge-transfer of cyclic alcohols and iron catalysts, providing a practical method for site-specific and remote arylation of ketones. The synergistic use of photocatalysis with convergent paired electrolysis can provide alternative avenues for metal-catalyzed radical coupling reactions.

Pd(0)-Catalyzed Asymmetric Intramolecular Grignard-Type Reaction of Vinyl Iodide-Carbonyl.

The insertion of carbonyl into C(sp2)-Pd(II) σ-bond (Grignard-type addition) was not established until the 1990s. While this elemental reaction has been well explored since then, its application in Pd(0) asymmetric catalysis remain elusive. Herein, we report the Pd(0)-catalyzed asymmetric intramolecular Grignard-type reaction of vinyl iodide-carbonyl in the presence of HCO2H additive, affording cyclic allylic alcohol with good to excellent enantioselectivity and diastereoselectivity. Mechanistic studies suggested that besides serving as an efficient reductant, HCO2H is also capable of facilitating protonation of the involved secondary alkoxyl-Pd(II), thus completely suppressing the β-H elimination. Moreover, no KIE was found in the competing reaction between vinyl iodide-aldehyde and 1-deuterated one, demonstrating the facile step of aldehyde insertion.

Three-Component Synthesis of Multiple Functionalized Allenes via Copper/Photoredox Dual Catalyzed 1,4-Alkylcyanation of 1,3-Enynes.

Efficient access to multiple functionalized allenes via a three component 1,4-alkylcyanation of enynes with cyclic alcohol derivatives in the presence of trimethylsilyl cyanide (TMSCN) under copper/photoredox dual catalysis has been developed. Both easily transformable aldehyde and cyano groups were introduced to tetra-substituted allenes through light-induced C-C bond cleavage of cyclic butanol and pentanol derivatives. The reactions proceeded smoothly under mild conditions with broad functional groups tolerance.

Dehydrogenation and Transfer Hydrogenation of Alkenones to Phenols and Ketones on Carbon-Supported Noble Metals.

The catalytic dehydrogenation of substituted alkenones on noble metal catalysts supported on carbon (Pt/C, Pd/C, Rh/C, and Ru/C) was investigated in an organic phase under inert conditions. The dehydrogenation and semihydrogenation of the enone starting materials resulted in aromatic compounds (primary products), saturated cyclic ketones (secondary products), and cyclic alcohols (minor products). Pd/C exhibits the highest catalytic activity, followed by Pt/C and Rh/C. Aromatic compounds remain the primary products, even in the presence of hydrogen donors. Joint experimental and theoretical analyses showed that the four catalytic materials stabilize a common dienol intermediate on the metal surfaces, formed by keto-enol tautomerization. This intermediate subsequently forms aromatic products upon dehydrogenation. The binding orientation of the enone reactants on the catalytic surface is strongly metal-dependent, as the M-O bond distance changes substantially according to the metal. The longer M-O bonds (Pt: 2.84 Å > Pd: 2.23 Å > Rh: 2.17 Å > Ru: 2.07 Å) correlate with faster reaction rates and more favorable keto-enol tautomerization, as shorter distances correspond to a more stabilized starting material. Tautomerization is shown to occur via a stepwise surface-assisted pathway. Overall, each of the studied metals exhibits a distinct balance of enthalpy and entropy of activation (ΔH°‡, ΔS°‡), offering unique possibilities in the realm of enone dehydrogenation reactions that can be achieved by suitable selection of catalytic materials.

Transformation of the pheromone 3‐methyl‐2‐cyclohexen‐1‐ol in the presence of [RuClCp (PTA)2] and [RuCp (OH2)(PTA)2]CF3SO3

The catalytic conversion of the substituted cyclic allylic alcohol 3‐methyl‐2‐cyclohexen‐1‐ol was studied in the presence of the metal complexes [RuClCp (PTA)2] (1) and [RuCp (OH2)(PTA)2]CF3SO3 (2) (PTA = 1,3,5‐triaza‐7‐phosphaadamantane) in different media such as water, methanol, and biphasic water/cyclohexane. Slight changes of the reaction conditions led to the isomerization to 3‐methylcyclohexanone, oxidation to 3‐methyl‐2‐cyclohexenone, or 1,3‐transposition to 1‐methyl‐2‐cyclohexen‐1‐ol. The 1,3‐transposition and oxidation reactions took place in water, and the selective formation of the isomerization product was achieved in freshly dried methanol, or biphasic water/cyclohexane mixture, achieving the highest TON values known to date. Furthermore, the reactivity of 3‐methyl‐2‐cyclohexen‐1‐ol in water was also investigated in the absence of a catalyst, revealing the formation of the 1,3‐transpostion product 1‐methyl‐2‐cyclohexen‐1‐ol and the etherification product 1‐methyl‐3‐(3‐methyl‐2‐cyclohexen‐1‐yl)oxycyclohexene. Finally, key mechanistic aspects of the different reaction pathways were enlightened by NMR spectroscopy.

Photocatalytic metal‐free oxidation of alcohols with molecular oxygen in supercritical CO2 medium

AbstractNear‐UV‐light‐induced oxidative conversion of cyclic and linear alcohols into corresponding carbonyl compounds was achieved in the supercritical CO2 medium under the action of molecular oxygen in the presence of 2‐fluoroanthraquinone (1 mol %), a simple and available metal‐free photocatalyst. A thorough examination of the impact of various process parameters on the reaction outcome allowed to identify a narrow density area at ~0.3 g/cm3 in the vicinity of the medium critical point and optimal reaction conditions (~45 °C, ~8.4 MPa) where up to 99 % conversions and 65–93 % yields of the oxidation products could be attained. Furthermore, it has been shown that compressed atmospheric air, a far cheaper and safer oxidizer than pure oxygen, can be applied to the reaction. Based on the experimental data, a plausible mechanism of the photocatalytic process has been proposed comprising photocatalyst excitation with near‐UV light followed by the hydrogen atom transfer (HAT) as the key stages.

Sulfonic Resins as Catalysts for the Oxidation of Alcohols with H2O2/KBr

Sulfonic resins can replace homogeneous sulfonic acids in the oxidation of alcohols with the H2O2/KBr system. The performance of different resins was tested with methyl 9(10)-hydroxystearate, a secondary fatty alcohol. The structural features of the resin were more important than the acid strength for the catalytic performance of this reaction. The optimization of the reaction conditions allows the recovery of the resin, although regeneration is required due to the active role of KBr, and a significant loss of sulfonic groups can be detected after nine runs. In the case of primary fatty alcohols, the oxidation leads to carboxylic acids, which are esterified with the starting alcohol under the acidic conditions. For cyclic secondary alcohols, the steric hindrance around the hydroxyl group seems to be important for the efficiency of the oxidation to ketone.

Preparation of Spirocyclic Vinylic Carbonates from Allylic Alcohols.

We present the synthesis of exo- and endo-spirovinylethylene carbonates, starting from various cyclic allylic alcohols. This one-pot cascade reaction to the spirocyclic scaffold was optimized using a design of experiments approach. The introduction of spirovinylethylene carbonates broadens the scope of using these in catalytic applications and provides an easy synthetic entry into spirocyclic scaffolds of various ring sizes.

Bridging the incompatibility gap in dual asymmetric catalysis over a thermoresponsive hydrogel-supported catalyst

The integration of dual asymmetric catalysis is highly beneficial for the synthesis of organic molecules with multiple stereocenters. However, two major issues that need to be addressed are the intrinsic deactivation of dual-species and the extrinsic conflict of reaction conditions. To overcome these concerns, we have utilized the compartmental and thermoresponsive properties of poly(N-isopropylacrylamide) (PNIPAM) to develop a cross-linked PNIPAM-hydrogel-supported bifunctional catalyst. This catalyst is designed with Rh(diene) species situated on the outer surface and Ru(diamine) species positioned within the interior of the hydrogel. The compartmental function of PNIPAM in the middle overcomes intrinsic mutual deactivations between the dual-species. The thermoresponsive nature of PNIPAM allows for precise control of catalytic pathways in resolving external conflicts by controlling the reaction switching between an Rh-catalyzed enantioselective 1,4-addition at 50°C and a Ru-catalyzed asymmetric transfer hydrogenation (ATH) at 25°C. As we envisioned, this sequential 1,4-addition/reduction dual enantioselective cascade reaction achieves a transformation from incompatibility to compatibility, resulting in direct access to γ-substituted cyclic alcohols with dual stereocenters in high yields and enantio/diastereoselectivities. Mechanistic investigation reveals a reversible temperature transition between 50°C and 25°C, ensuring a cascade process comprising a 1,4-addition followed by the ATH process.

Synthesis of ω-functionalized ketones from strained cyclic alcohols by ring-opening and cross-recombination between alkyl and N-oxyl radicals.

Radical ring-opening oxyimidation of cyclobutanols and cyclopropanols with the formation of ω-functionalized ketones was discovered. The oxidative C-O coupling proceeds via the interception of a primary alkyl radical generated from a cyclic alcohol with a reactive radical generated in situ, which is an electron-deficient N-oxyl radical. The developed conditions allow for the balanced generation rates of carbon- and N-oxyl radicals, which are necessary for their selective cross-recombination. Thus, typical competitive dimerization processes of carbon-centered radicals, their intermolecular cyclization, and N-oxyl radical self-decay are suppressed. The method is applicable to a wide range of cyclobutanols and results in oxyimidated ketones in yields of up to 82%.

Biocatalytic asymmetric ring-opening of meso-epoxides to enantiopure cyclic trans-β-amino alcohols involving a key amine transaminase

Biocatalytic asymmetric ring-opening of meso-epoxides to chiral cyclic β-amino alcohols with good conversions and excellent enantioselectivity.

Understanding the active role of water in laboratory chamber studies of reactions of the OH radical with alcohols of atmospheric relevance.

In this work, we studied the reactions of three cyclic aliphatic alcohols with OH at room temperature, atmospheric pressure and different humidities in a Teflon reaction chamber. It was determined that the lower the solubility of the alcohol in water, the larger the effect of the humidity on the acceleration of the reaction. This experimental evidence allows suggesting that the acceleration is due to the reaction of the co-adsorbed reactants at the air-water interface of a thin water film deposited on the Teflon walls of the reaction chamber, instead of between co-reactants dissolved in the water film or due to gas phase catalysis as previously suggested. Therefore, formation of thin water films on different surfaces could have some implications on the tropospheric chemistry of these alcohols in the tropical regions of the planet with high humidity.

An Overview: Synthesis of Menthol using Heterogeneous Catalysis

Abstract: Essential oils are widely used in cosmetic and personal care products. These essential oils such as menthol, limonene, rose oil, and jasmine oil are extracted from plants and also prepared in the laboratory. Menthol is the most common cyclic monoterpene alcohol, which has been produced due to its demand in various industries worldwide. In the literature, there were many protocols reported for the synthesis of menthols from natural or synthetic precursors. In this review, we summarized the synthesis of menthol from citral, citronellal, and pulegone using various heterogeneous catalysts under different conditions. Considering the world’s demand for menthol in food preservatives and scents, the right optimization of citronella extraction and its conversion is highly important. It can be used in pharmaceutical industries due to the presence of active substances. The presence of flavored compounds has the potential to enhance the nutritional value of food. This review will be very helpful for researchers who are working on menthol synthesis in industry and institutions. The determination of direct conversion to menthol over indirect conversion can be proven to be effective for industrial use as it will be more economical and time-saving.

VALIDATION OF CONTINUOUS FLOW METAL PLATE REACTORS IN THE TERPENE KETONE SYNTHESIS BY ALCOHOL OXIDATION

The present study elucidates the oxidation of alcohols to terpene ketones using dichloro(p-cymene) ruthenium (II) dimer catalyst by continuous flow process using a metal plate reactor. The synthesized products were separated and validated using GC, GCMS, 1H-NMR, and 13C-NMR techniques. The reaction process exhibited product yield in the range of 80-95% on a scale of 1-80 grams. Optimization studies were conducted to calibrate the reaction conditions to improve the product yield. The scope of the reaction was explored using aromatic, cyclic, and aliphatic alcohols under optimized conditions, which resulted in high yields of terpene ketones. A reaction mechanism is proposed for the oxidation of alcohols by a continuous flow process. The significant advantages of the current protocol include synthesis at mild conditions, safer handling of reagents, flexibility to tune reaction conditions, and straightforward scale-up in the range of 1- 80 grams with high efficiency and reproducibility.

Dual transition metal electrocatalysis enables selective C(sp3)-C(sp3) bond cleavage and arylation of cyclic alcohols.

We report a dual transition metal electrocatalytic approach for C(sp3)-C(sp3) bond cleavage and arylation of cyclic alcohols, providing an efficient and sustainable method for site-specific arylation of ketones. The reaction involves electrophotochemical cerium-catalysed generation of alkoxyl radicals from readily accessible alcohols. Subsequently, homolytic cleavage of the β-C-C bond leads to the generation of carbon-centered radicals that could be effectively utilized by nickel catalysis powered by cathode reduction to deliver the remote arylated ketone products.

Selective synthesis of cyclic alcohols from cycloalkanes using nickel(ii) complexes of tetradentate amidate ligands.

Selective functionalisation of hydrocarbons using transition metal complexes has evoked significant research interest in industrial chemistry. However, selective oxidation of unactivated aliphatic C-H bonds is challenging because of the high bond dissociation energies. Herein, we report the synthesis, characterisation and catalytic activity of nickel(ii) complexes ([Ni(L1-L3)(OH2)2](ClO4)2 (1-3)) of monoamidate tetradentate ligands [L1: 2-(bis(pyridin-2-ylmethyl)amino)-N-phenylacetamide, L2: 2-(bis(2-pyridin-2-ylmethyl)amino)-N-(naphthalen-1-yl)acetamide, L3: N-benzyl-2-(bis(pyridin-2-ylmethyl)amino)acetamide] in selective oxidation of cycloalkanes using m-CPBA as the oxidant. In cyclohexane oxidation, catalysts showed activity (TON) in the order 1 (654) > 2 (589) > 3 (359) with a high A/(K + L) ratio up to 23.6. Using catalyst 1, the substrate scope of the reaction was broadened by including other cycloalkanes such as cyclopentane, cycloheptane, cyclooctane, adamantane and methylcyclohexane. Further, the Fenton-type reaction in the catalytic cycle was discarded based on the relatively high 3°/2° ratio of 8.6 in adamantane oxidation. Although the formation of chlorinated products during the reactions confirmed the contribution of the 3-chlorobenzoyloxy radical mechanism, the high alcohol selectivity obtained for the reactions indicated the participation of nickel-based oxidants in the oxidation process.

Evaluation of Chemical Constituents and Antioxidant Activity of Extracts of Nardostachys jatamansi (D. Don) DC.

Nardostachys jatamansi is an endangered medicinal plant of the Caprifoliaceae family. The main aim of this study was to evaluate the metabolites and their biological activities. The shade dried, powdered plant materials were subjected to successive ultrasonic extraction with solvents hexane, chloroform, ethyl acetate, and methanol in the increasing order of polarity. Flavonoids, terpenoids, saponins, phenolic volatile oils, and alkaloids were discovered in the phytochemical screening. Gas chromatography mass spectrometry analysis identified 13, 10, and 6 chemical compounds in hexane, chloroform, and ethyl acetate extracts, respectively. Cyclic saturated hydrocarbons, organic acids, alcohol, and ester were the main constituents of extracts verified by GC-MS. Chloroform extracts had a higher phenolic content (49.53 mg GAE/g) than ethyl acetate extracts (44.41 mg GAE/g). Chloroform extracts had a higher total flavonoid concentration (18.42 mg QE/g) than ethyl acetate extracts (10.57 mg QE/g). The half-maximum inhibitory concentration (IC50) of the chloroform and ethyl acetate extracts revealed moderate results to antioxidant activity.

Optimizing pyrolysis parameters and product analysis of a fluidized bed pilot plant for Leucaena leucocephala biomass

This study aimed to optimize the production of bio-oil from Leucaena leucocephala wood using a fluidized bed reactor. Response surface methodology was used to optimize the fast pyrolysis through three operational parameters: pyrolysis temperature, nitrogen flow rate, and temperature of the first condensation stage. The optimum conditions obtained for bio-oil production were 500 °C, 26.4 L min–1, that is, about 3.3 times the minimum fluidization flow, and 80 °C, respectively. The bio-oil obtained under optimum conditions was of good quality and did not require further treatment. Physical properties of the bio-oil were analysed according to ASTM D7544-12. In addition, the chemical composition of the non-condensed gases and bio-oil were identified using GC–MS. The non-condensed gases were found to contain mainly ketones and lignin derivatives, while the bio-oil contained cyclic ketones, alcohol ethers, aromatic alcohols, and lignin derivatives. The study found that increasing the pyrolysis temperature did not significantly increase the yield of H2 and CO for syngas production. Regarding the solid obtained, a large amount of unreacted material (66.7 wt.%) is generated at 400 °C, and as the temperature is increased, a high-quality biochar is obtained.

Co-pyrolysis of bamboo biomass with polypropylene coverall: Distributed activation energy modeling and pyrolysate composition studies

This study evaluates the pyrolysis kinetics and resource recovery potential from mixtures of bamboo sawdust (BS) biomass, and a COVID-19 waste material, body coverall (BC). The pyrolysis kinetics of BS, BC and their binary mixtures was modeled using distributed activation energy modeling approach. BS pyrolysis was described using three pseudocomponents, viz., cellulose, hemicellulose and lignin, and BC using two pseudocomponents, polypropylene and an additive. For pyrolysis of individual BS and BC, the activation energy was highest for lignin (272.1 kJ mol−1) and the additive (321.7 kJ mol−1) pseudocomponent. The activation energy (240.7 kJ mol−1) and change in enthalpy (234.9 kJ mol−1) were found to be the lowest for lignin for the blend BS:BC (3:1 wt/wt). Analytical pyrolysis revealed alkenes (63.3%) and oxygen containing aromatics (57.4%) as the major compounds from BC and BS, respectively. Cyclic alcohols were the major compounds from pyrolysis of BS–BC mixtures. This study demonstrates that blending BC with BS lowers the energy barrier for pyrolysis to generate valuable chemicals.

Creation of a Highly Active Small Cu-Based Catalyst Derived from Copper Aluminium Layered Double Hydroxide Supported on α-Al2 O3 for Acceptorless Alcohol Dehydrogenation.

A highly dispersed carbonate-intercalated Cu2+ -Al3+ layered double hydroxide (CuAl LDH) was created on an unreactive α-Al2 O3 surface (CuAl LDH@α-Al2 O3 ) via a simple coprecipitation method of Cu2+ and Al3+ under alkaline conditions in the presence of α-Al2 O3 . A highly reducible CuO nanoparticles was generated, accompanied by the formation of CuAl2 O4 on the surface of α-Al2 O3 (CuAlO@α-Al2 O3 ) after calcination at 1073 K in air, as confirmed by powder X-ray diffraction (XRD) and Cu K-edge X-ray absorption near edge structure (XANES). The structural changes during the progressive heating process were monitored by using in-situ temperature-programmed synchrotron XRD (tp-SXRD). The layered structure of CuAl LDH@α-Al2 O3 completely disappeared at 473 K, and CuO or CuAl2 O4 phases began to appear at 823 K or 1023 K, respectively. Our synthesised CuAlO@α-Al2 O3 catalyst was highly active for the acceptorless dehydrogenation of benzylic, aliphatic, or cyclic aliphatic alcohols; the TON based on the amount of Cu increased to 163 from 3.3 of unsupported CuAlO catalyst in 1-phenylethanol dehydrogenation. The results suggested that Cu0 was obtained from the reduction of CuO in the catalyst matrix during the reaction without separate reduction procedure and acted as a catalytically active species.