CO2-Catalyzed Oxidation of Benzylic and Allylic Alcohols with DMSO

CO2-Promoted and Copper-Catalyzed Dehydroxylative Coupling of Benzylic Alcohols by the NaBH4/I2 System

An efficient and CO2-promoted dehydroxylative coupling of benzylic alcohols catalyzed by ligand-free cuprous chloride has been achieved. The discovered catalytic reductive coupling reaction is a newly C-C bond-forming transformation of alcohols. Mechanistic insight is gained through control reactions.

Harnessing alcohols as sustainable reagents for late-stage functionalisation: synthesis of drugs and bio-inspired compounds

Alcohol is ubiquitous with unparalleled structural diversity and thus has wide applications as a native functional group in organic synthesis. It is highly prevalent among biomolecules and offers promising opportunities for the development of chemical libraries. Over the last decade, alcohol has been extensively used as an environmentally friendly chemical for numerous organic transformations. In this review, we collectively discuss the utilisation of alcohol from 2015 to 2023 in various organic transformations and their application toward intermediates of drugs, drug derivatives and natural product-like molecules. Notable features discussed are as follows: (i) sustainable approaches for C-X alkylation (X = C, N, or O) including O-phosphorylation of alcohols, (ii) newer strategies using methanol as a methylating reagent, (iii) allylation of alkenes and alkynes including allylic trifluoromethylations, (iv) alkenylation of N-heterocycles, ketones, sulfones, and ylides towards the synthesis of drug-like molecules, (v) cyclisation and annulation to pharmaceutically active molecules, and (vi) coupling of alcohols with aryl halides or triflates, aryl cyanide and olefins to access drug-like molecules. We summarise the synthesis of over 100 drugs via several approaches, where alcohol was used as one of the potential coupling partners. Additionally, a library of molecules consisting over 60 fatty acids or steroid motifs is documented for late-stage functionalisation including the challenges and opportunities for harnessing alcohols as renewable resources.

Multifunctional Biomass-Based Ionic Liquids/CuCl-Catalyzed CO2-Promoted Hydration of Propargylic Alcohols: A Green Synthesis of α-Hydroxy Ketones

α-Hydroxy ketones are a class of vital organic skeletons that generally exist in a variety of natural products and high-value chemicals. However, the traditional synthetic route for their production involves toxic Hg salts and corrosive H2SO4 as catalysts, resulting in harsh conditions and the undesired side reaction of Meyer-Schuster rearrangement. In this study, CO2-promoted hydration of propargylic alcohols was achieved for the synthesis of various α-hydroxy ketones. Notably, this process was catalyzed using an environmentally friendly and cost-effective biomass-based ionic liquids/CuCl system, which effectively eliminated the side reaction. The ionic liquids utilized in this system are derived from natural biomass materials, which exhibited recyclability and catalytic activity under 1 bar of CO2 pressure without volatile organic solvents or additives. Evaluation of the green metrics revealed the superiority of this CuCl/ionic liquid system in terms of environmental sustainability. Further mechanistic investigation attributed the excellent performance to the ionic liquid component, which exhibited multifunctionality in activating substrates, CO2 and the Cu component.

Nickel-Catalyzed Reductive Allylation of Aldehydes with Allylic Alcohols in the Presence of CO2

CO2-assisted and Ni-catalyzed direct reductive allylation of aldehydes utilizing allylic alcohols as allylic precursor has been reported. Various homoallyl alcohols could be synthesized in excellent yield with enhanced regioselectivity and stereoselectivity for alkyl- and aryl-substituted aldehydes under mild conditions. For different substrates, proper collocation of the catalytic precursor and ligand is crucial. Preliminary mechanistic studies supported the reaction pathway through a sequential allyl hydrocarbonate formation/allylnickelation/coordination insertion process by the Ni(I)/Ni(III) catalytic cycle, which has been proven by cyclic voltammetry analysis.

Insertion of CO2 and CS2 into Bi-N bonds enables catalyzed CH-activation and light-induced bismuthinidene transfer

The uptake and release of small molecules continue to be challenging tasks of utmost importance in synthetic chemistry. The combination of such small molecule activation with subsequent transformations to generate unusual reactivity patterns opens up new prospects for this field of research. Here, we report the reaction of CO₂ and CS₂ with cationic bismuth(iii) amides. CO₂-uptake gives isolable, but metastable compounds, which upon release of CO₂ undergo CH activation. These transformations could be transferred to the catalytic regime, which formally corresponds to a CO₂-catalyzed CH activation. The CS₂-insertion products are thermally stable, but undergo a highly selective reductive elimination under photochemical conditions to give benzothiazolethiones. The low-valent inorganic product of this reaction, Bi(i)OTf, could be trapped, showcasing the first example of light-induced bismuthinidene transfer.

CO2-Promoted and Nickel-Catalyzed Direct Hydroallylation of Terminal Alkynes with Allylic Alcohols: Access to 1,4-Dienes

CO₂-promoted and Ni-catalyzed direct hydroallylation of terminal alkynes with allylic alcohols has been achieved. Various 1,4-dienes could be synthesized in good yield with excellent Markovnikov selectivity for alkyl- and aryl-substituted terminal alkynes under mild reaction conditions. A gram-scale reaction gives considerable yield. Preliminary mechanistic studies support the reaction pathway through sequential carboxylation/allylnickelation/lithium bicarbonate nickelation/transmetalation in the hydroallylation of alkynes with allylic alcohols in the presence of CO₂.

Polyoxometalate-Supported Copper(I)-Pyrazole Complex: Unusual Stability, Geometrical Isomers, Organic Transformation, and Computation

We have described the synthesis and characterization of a polyoxometalate (POM)-supported copper(I)-pyrazole complex, [Cu^I(C₁₅H₁₂N₂)₂] [PW₁₂O₄₀{Cu^I(C₁₅H₁₂N₂)₂}₂]·CH₃OH (1). There are three Cu(I)-pyrazole coordination complexes in compound 1, out of which two are supported by the {PW₁₂O₄₀}^3- Keggin POM by coordinate covalent bonds from the POM surface through oxygen donors to the Cu(I) centers of two Cu(I) complexes and one remains uncoordinated to the POM surface, acting as a cationic complex species in the crystals of 1. The POM-coordinated Cu(I) complexes have a T-shaped geometry, and the uncoordinated Cu(I) complex is a linear one. During the solvothermal synthesis of compound 1, remarkably, the associated 1,5-diphenylpyrazole ligand is formed from cinnamaldehyde phenylhydrazone through oxidative cyclization at the cost of Cu(II) reduction to Cu(I), and then, these two (copper(I) and pyrazole ligand) form the coordination complex. Compound 1 undergoes desolvation on heating the single crystals of compound 1 at 55 °C in the aerial atmosphere with the formation of the desolvated compound [Cu^I(C₁₅H₁₂N₂)₂][PW₁₂O₄₀{Cu^I(C₁₅H₁₂N₂)₂}₂] (2). Interestingly, when an aqueous suspension of compound 1 is bubbled with O₂ gas at room temperature, it undergoes solid-to-solid transformation, resulting in the formation of the compound [Cu^I(C₁₅H₁₂N₂)₂]₃[PW₁₂O₄₀] (3). Compounds 1, 2, and 3 have been characterized by routine spectral analyses (including cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) studies) and unambiguously by single-crystal X-ray crystallography. We have performed density functional theory (DFT) calculations on compound 1 to understand the rationale of its unusual stability toward oxidation.

CO2 -Promoted Direct Acylation of Amines and Phenols by the Activation of Inert Thioacid Salts

Herein a carbon dioxide-promoted synthetic approach for the direct amidation between unactivated thioacid salts and amines under mild conditions was developed for a wide range of substrates. The method afforded amides in good to excellent yields under transition-metal-free and activation-reagent-free conditions, in sharp contrast to early methodologies on amide synthesis based on transition-metal catalysis. The method offered a greener and transition metal-free protocol applicable to pharmaceuticals preparations. Phenolic compounds were also found to be suitable acylation substrates with potassium thiosulfide KHS as the only byproduct. Moreover, this approach was applied to amide synthesis of valuable bio-active molecules such as moclobemide, melatonin, and a fungicide. Insights into the reaction mechanism involving carbon dioxide were provided through NMR spectroscopy and computational calculations. A plausible mechanism was proposed that involves weak interactions between carbon dioxide and potassium thioacetate in a dynamic equilibrium state formation of a six-membered ring.

Structural derivatization strategies of natural phenols by semi-synthesis and total-synthesis

Structural derivatization of natural products has been a continuing and irreplaceable source of novel drug leads. Natural phenols are a broad category of natural products with wide pharmacological activity and have offered plenty of clinical drugs. However, the structural complexity and wide variety of natural phenols leads to the difficulty of structural derivatization. Skeleton analysis indicated most types of natural phenols can be structured by the combination and extension of three common fragments containing phenol, phenylpropanoid and benzoyl. Based on these fragments, the derivatization strategies of natural phenols were unified and comprehensively analyzed in this review. In addition to classical methods, advanced strategies with high selectivity, efficiency and practicality were emphasized. Total synthesis strategies of typical fragments such as stilbenes, chalcones and flavonoids were also covered and analyzed as the supplementary for supporting the diversity-oriented derivatization of natural phenols.

Challenges and recent advancements in the transformation of CO2 into carboxylic acids: straightforward assembly with homogeneous 3d metals

Transformation of carbon dioxide (CO2) into valuable organic carboxylic acids is essential for maintaining sustainability. In this review, such CO2 thermo-, photo- and electrochemical transformations under 3d-transition metal catalysis are described from 2017 until 2022.

Photocatalytic synthesis of tetra-substituted furans promoted by carbon dioxide

A CO2-promoted transition metal-free photocatalytic synthesis of tetra-substituted furan derivatives from 1,3-diketones as the only starting material.

Polyoxometalate-Incorporated Framework as a Heterogeneous Catalyst for Selective Oxidation of C-H Bonds of Alkylbenzenes

Developing new catalysts for highly efficient and selective oxidation of saturated C-H bonds is significant due to their thermodynamic strength. Via incorporation of PW₁₂O₄₀^3-, pyridine-2,5-dicarboxylic acids (pydc), and Fe(III) ions into one framework, a new polyoxometalate-based metal-organic framework, [HFe₄O₂(H₂O)₄(pydc)₃PW₁₂O₄₀]·10.5H₂O (FeW-PYDC), was successfully prepared by a hydrothermal method. Interestingly, FeW-PYDC features a three-dimensional porous structure with {Fe₄O₂} interconnecting with PW₁₂O₄₀^3- units. FeW-PYDC displayed excellent performance in the selective oxidation of C-H bonds of alkylbenzenes with high conversion (95.7%) and selectivity (96.6%). As an effective heterogeneous catalyst, FeW-PYDC demonstrates good reusability and structural stability.

Heterogeneous Organocatalysts for the Reduction of Carbon Dioxide with Silanes

The utilization of carbon dioxide (CO₂ ) as feedstock for chemical industries is gaining interest as a sustainable alternative to nonrenewable fossil resources. However, CO₂ reduction is necessary to increase its energy content. Hydrosilane is a potential reducing agent that exhibits excellent reactivity under ambient conditions. CO₂ hydrosilylation yields versatile products such as silylformate and methoxysilane, whereas formamides and N-methylated products are obtained in the presence of amines. In these transformations, organocatalysts are considered as the more sustainable choice of catalyst. In particular, heterogeneous organocatalysts featuring precisely designed active sites offer higher efficiency due to their recyclability. Herein, an overview is presented of the current development of basic organocatalysts immobilized on various supports for application in the chemical reduction of CO₂ with hydrosilanes, and the potential active species parameters that might affect the catalytic activity are identified.

CO2 -Enabled Cyanohydrin Synthesis and Facile Iterative Homologation Reactions*

Thermodynamic and kinetic control of a chemical process is the key to access desired products and states. Changes are made when a desired product is not accessible; one may manipulate the reaction with additional reagents, catalysts and/or protecting groups. Here we report the use of carbon dioxide to accelerate cyanohydrin synthesis under neutral conditions with an insoluble cyanide source (KCN) without generating toxic HCN. Under inert atmosphere, the reaction is essentially not operative due to the unfavored equilibrium. The utility of CO₂ -mediated selective cyanohydrin synthesis was further showcased by broadening Kiliani-Fischer synthesis under neutral conditions. This protocol offers an easy access to a variety of polyols, cyanohydrins, linear alkylnitriles, by simply starting from alkyl- and arylaldehydes, KCN and an atmospheric pressure of CO₂ .

Carbon dioxide-promoted palladium-catalyzed dehydration of primary allylic alcohols: access to substituted 1,3-dienes

A carbon dioxide promoted dehydration reaction of primary allylic alcohols gives synthetically important substituted 1,3-dienes in good yields under milder conditions compared with the reaction using a heterogeneous catalyst or carbon monoxide.

Transition Metal-Free Synthesis of Carbamates Using CO2 as the Carbon Source

Utilization of carbon dioxide as a C1 synthon is highly attractive for the synthesis of valuable chemicals. However, activation of CO₂ is highly challenging, owing to its thermodynamic stability and kinetic inertness. With this in mind, several strategies have been developed for the generation of carbon-heteroatom bonds. Among these, formation of C-N bonds is highly attractive, especially, when carbamates can be synthesized directly from CO₂ . This Minireview focuses on transition metal-free approaches for the fixation of CO₂ to generate carbamates for the production of fine chemicals and pharmaceuticals. Within the past decade, transition metal-free approaches have gained increasing attention, but traditional reviews have rarely focused on these approaches. Direct comparisons between such methods have been even more scarce. This Minireview seeks to address this discrepancy.

Graphene oxide-iridium nanocatalyst for the transformation of benzylic alcohols into carbonyl compounds

A catalyst constructed from graphene oxide and iridium chloride exhibited high activity and reliability for the selective transformation of benzylic alcohols into aromatic aldehydes or ketones. Instead of thermal reaction, the transformation was performed under ultrasonication, a green process with low byproduct, high atomic yield and high selectivity. Experimental data obtained from spherical-aberration corrected field emission TEM (ULTRA-HRTEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy and Raman spectra confirm the nanostructure of the title complex. Noticeably, the activity and selectivity for the transformation of benzylic alcohols remained unchanged within 25 catalytic cycles. The average turn over frequency is higher than 5000 h⁻¹, while the total turnover number (TON) is more than one hundred thousand, making it a high greenness and eco-friendly process for alcohol oxidation.

Graphene oxide–iridium nanostructure act as a robust catalyst exhibiting high activity and reliability for the selective transformation of benzylic alcohols into aromatic aldehydes or ketones.

Solvent and additive-free efficient aerobic oxidation of alcohols by a perovskite oxide-based heterogeneous catalyst

A perovskite oxide has been utilized for the solvent and additive-free heterogeneous oxidation of various alcohols.

Industrial carbon dioxide capture and utilization: state of the art and future challenges

This review covers the sustainable development of advanced improvements in CO₂ capture and utilization.

I2-DMSO-H2O: A Metal-Free Combination System for the Oxidative Addition of Alkynes to Access (E)-α-Iodo-β-methylsulfonylalkenes

A simple and green reaction was discovered for iodization-methylsulfoxidation of alkynes to access (E)-α-iodo-β-methylsulfonylalkenes. This is the first report for the synthesis of iodovinyl methylsulfones by employing alkynes to react with molecular iodine (I₂), dimethyl sulfoxide (DMSO), and H₂O. Additionally, this protocol represents a new avenue for utilizing DMSO as the source of the -SO₂Me group and H₂O as the "O" source for the construction of the -SO₂Me group from DMSO, which is a valuable finding.

Visible-Light-Mediated Dearomatisation of Indoles and Pyrroles to Pharmaceuticals and Pesticides

Dearomatisation of indole derivatives to the corresponding isatin derivatives has been achieved with the aid of visible light and oxygen. It should be noted that isatin derivatives are highly important for the synthesis of pharmaceuticals and bioactive compounds. Notably, this chemistry works excellently with N-protected and protection-free indoles. Additionally, this methodology can also be applied to dearomatise pyrrole derivatives to generate cyclic imides in a single step. Later this methodology was applied for the synthesis of four pharmaceuticals and a pesticide called dianthalexin B. Detailed mechanistic studies revealed the actual role of oxygen and photocatalyst.

Iodine-Mediated Oxidative Rearrangement of α,β-Unsaturated Diaryl Ketones: A Facile Access to 1,2-Diaryl Diketones

A metal-free oxidative rearrangement was explored for the synthesis of 1,2-diaryl diketones by utilizing α,β-unsaturated diaryl ketones and I2/TBHP in good to high yields. The reaction proceeds via oxidative aryl migration, followed by C-C bond cleavage. A simple and high-yielding protocol was developed for the synthesis of a wide range of 1,2-diaryl diketones, which are the backbone for a variety of medicinally important molecules.

CO2/Photoredox-Cocatalyzed Tandem Oxidative Cyclization of α-Bromo Ketones and Amines To Construct Substituted Oxazoles

CO₂/photoredox-cocatalyzed tandem oxidative cyclization of α-bromo ketones and amines for the preparation of substituted oxazoles has been achieved. The avoidance of using both transition-metal catalysts and peroxides makes this method more sustainable and renewable.

Transition-metal-free regioselective construction of 1,5-diaryl-1,2,3-triazoles through dehydrative cycloaddition of alcohols with aryl azides mediated by SO2F2

A novel, simple and practical method for mild, efficient, cost-effective and regioselective synthesis of highly valuable 1,5-diaryl-1,2,3-triazoles was achieved through dehydrative annulation of readily available alcohols with aryl azides. The reaction proceeded at room temperature, without any metal catalysts, exhibiting excellent compatibility to a large variety of functional groups (>50 examples), resulting in up to quantitative yields.

Selectfluor™-catalyzed oxidative cyclization of ynamides enables facile synthesis of oxazolidine-2,4-diones

A Selectfluor™-catalyzed oxidative cyclization of ynamides employing DMSO as the solvent and oxidant was achieved, affording oxazolidine-2,4-diones in moderate to excellent yields with high chemo-selectivity. The method offers an attractive alternative to existing protocols.

Recent advances in nucleophile-triggered CO2-incorporated cyclization leading to heterocycles

CO₂, as a sustainable, feasible, abundant one-carbon synthon, has been utilized in carboxylative cyclization, carbonylative cyclization, and reductive cyclization.

Selective Benzyl Alcohol Oxidation over Pd Catalysts

In the last decades, the selective liquid phase oxidation of alcohols to the corresponding carbonyl compounds has been a subject of growing interest. Research has focused on green methods that use “clean” oxidants such as O2 in combination with supported metal nanoparticles as the catalyst. Among the alcohols, benzyl alcohol is one of the most studied substrates. Indeed, benzyl alcohol can be converted to benzaldehyde, largely for use in the pharmaceutical and agricultural industries. This conversion serves as model reaction in testing new potential catalysts, that can then be applied to other systems. Pd based catalysts have been extensively studied as active catalytic metals for alcohol oxidation for their high activity and selectivity to the corresponding aldehyde. Several catalytic materials obtained by careful control of the morphology of Pd nanoparticles, (including bimetallic systems) and by tuning the support properties have been developed. Moreover, reaction conditions, including solvent, temperature, pressure and alcohol concentration have been investigated to tune the selectivity to the desired products. Different reaction mechanisms and microkinetic models have been proposed. The aim of this review is to provide a critical description of the recent advances on Pd catalyzed benzyl alcohol oxidation.