Versatile Building Block Research Articles

Multistep Biooxidation of 5-(Hydroxymethyl)furfural to 2,5-Furandicarboxylic Acid with H2O2 by Unspecific Peroxygenases.

5-(Hydroxymethyl)furfural (HMF) is a key platform chemical derived from renewable biomass sources, holding great potential as starting material for the synthesis of valuable compounds, thereby replacing petrochemical-derived counterparts. Among these valorised compounds, 2,5-furandicarboxylic acid (FDCA) has emerged as a versatile building block. Here we demonstrate the biocatalytic synthesis of FDCA from HMF via a one-pot three-step oxidative cascade performed via two operative steps under mild reaction conditions employing two unspecific peroxygenases (UPOs) using hydrogen peroxide as the only oxidant. The challenge of HMF oxidation by UPOs is the chemoselectivity of the first step, as one of the two possible oxidation products is only a poor substrate for further oxidation. The unspecific peroxygenase from Marasmius oreades (MorUPO) was found to oxidize 100 mM of HMF to 5-formyl-2-furoic acid (FFCA) with 95% chemoselectivity. In the sequential one-pot cascade employing MorUPO (TON up to 13535) and the UPO from Agrocybe aegerita (AaeUPO, TON up to 7079), 100 mM of HMF were oxidized to FDCA reaching up to 99% conversion and yielding 861 mg isolated pure crystalline FDCA, presenting the first example of a gram scale biocatalytic synthesis of FDCA involving UPOs.

Diversified Synthesis of Chiral Fluorinated Cyclobutane Derivatives Enabled by Regio- and Enantioselective Hydroboration.

The diversified synthesis of chiral fluorinated cyclobutane derivatives has remained a tough task in synthetic chemistry. Herein, we present a switchable paradigm for asymmetric hydroboration and formal hydrodefluorination of gem-difluorinated cyclobutenes via rhodium catalysis, providing chiral gem-difluorinated α-boryl cyclobutanes and monofluorinated cyclobutenes with excellent regio- and enantioselectivity, respevtively. The key to the success of the two transformations relies on an efficient, mild and highly selective rhodium-catalyzed asymmetric hydroboration with HBPin (pinacolborane), in which the subsequent addition of a base, and a catalytic amount of palladium if necessary, results in the formation of formal hydrodefluorination products with the four-membered ringretained. The obtained chiral gem-difluorinated α-boryl cyclobutanes are versatile building blocks, which provides a platform for the synthesis of enantioenriched fluorinated cyclobutane derivatives to a great diversity.

Diversified Synthesis of Chiral Fluorinated Cyclobutane Derivatives Enabled by Regio‐ and Enantioselective Hydroboration

The  diversified synthesis of chiral fluorinated cyclobutane derivatives has remained a tough task in synthetic chemistry. Herein, we present a switchable paradigm for asymmetric hydroboration and formal hydrodefluorination of gem‐difluorinated cyclobutenes via rhodium catalysis, providing chiral gem‐difluorinated α‐boryl cyclobutanes and monofluorinated cyclobutenes with excellent regio‐ and enantioselectivity, respevtively. The key to the success of the two transformations relies on an efficient, mild and highly selective rhodium‐catalyzed asymmetric hydroboration with HBPin (pinacolborane), in which the subsequent addition of a base, and a catalytic amount of palladium if necessary, results in the formation of formal hydrodefluorination products with the four‐membered ring retained. The obtained chiral gem‐difluorinated α‐boryl cyclobutanes are versatile building blocks, which provides a platform for the synthesis of enantioenriched fluorinated cyclobutane derivatives to a great diversity.

Solvent-promoted selective chemocatalytic hydroxymethylation of biomass furanic compounds

Functionalizing biomass-derived furanic chemicals is of great importance towards biorefinery processes but challenging, especially working at elevated substrate concentrations. We herein report the intervention of 1,4-dioxane co-solvent availably to catalyze hydroxymethylation of furfuryl alcohol (FA) in formalin over Hβ zeolite, giving high yield to 2,5-dihydroxymethylfuran (DHMF), a versatile building block. Impressively, the facilitating effect of 1,4-dioxane on DHMF production became more pronounced with increasing FA feeding concentration, and the yield raised from 19.5 % to 67.8 % from a high FA concentration of 10 wt%. The 1,4-dioxane served not only as a catcher of formaldehyde hydrate to access substrate FA, but also as a shield to restrain undesirable condensation side-reactions. The developed protocol demonstrated an excellent universality in boosting the hydroxymethylation of electrondrawing-group-free furanic molecules (e.g., furan, 2-methylfuran). The understanding of these solvation effects can be employed to effectively manipulate and improve the hydroxymethylation of furanic compounds.

Diazoacetonitrile: Safe and Green Synthesis through Continuous Processing

AbstractDiazo compounds, although possessing unique reactivity, have been widely rejected due to their highly hazardous preparation protocols. Diazoacetonitrile (DAN), a relatively stable diazo compound, has been overlooked despite its potential in chemical synthesis. The present study describes a microflow process for the simultaneous preparation of DAN in aqueous solution and its extraction in dichloromethane. The DAN productivity was optimized in terms of solvent, temperature, residence time, and pressure. This experimental work represents a breakthrough in delivering DAN continuously in a stable CH2Cl2 solution, enabling its utilization as a versatile building block for various synthetic processes and contributing to the development of new green synthetic processes.

Valorization of (Bio)Ethanol over MoO3/(WO3-ZrO2) Sol-Gel-like Catalysts

Bioethanol, which is currently produced commercially from a growing variety of renewable biomass and waste sources, is an appealing feedstock for the production of fuels and chemicals. The literature clearly shows that bioethanol is a versatile building block to be used in biorefineries. The ethanol conversion using several catalysts with acidic, basic, and redox characteristics results in a diverse assortment of high-value bioproducts. High-acidity tungsten zirconia-based catalysts are stated to compete with traditional zeolitic catalysts and can be employed in the dehydration of ethanol to ethylene, but for a low reaction temperature acetic acid is formed, which causes corrosion issues. WO3-ZrO2 (W/Zr = 1, atomic) catalysts modified with MoO3 were prepared by a sol-gel-like procedure and tested in a gas phase ethanol conversion in the presence of air. The citrate derived xerogels were annealed at 853 K for 12 h, allowing low surface area (<10 m2/g) materials with a Mo-W mixed-oxide-rich surface over tetragonal nanostructured zirconia. Catalysts with MoO3-loading produced mainly acetaldehyde, instead of ethylene, as a result of the high reducibility of Mo6+ when compared to W6+. During the reaction, the Mo6+ becomes partially reduced, but Mo6+/Mo5+ species are still active for methanol conversion with increased ethylene selectivity due to the high acidity of tetrahedral MOX species formed during the reaction. Adding water to ethanol, to simulate bioethanol, only leads to a slight inhibition in ethanol conversion over the MoO3/(WO3-ZrO2) catalysts. The results show that molybdenum oxide deposited on tungstated zirconia catalyst is active, with low sensitivity to water, for the valorization of bioethanol into high-value chemicals, such as ethylene and acetaldehyde, and whose selectivity can be tuned by changing the amount of MoO3 that is loaded. The MoO3/(WO3-ZrO2) catalysts prepared show catalytic behavior similar to that of noble metal-based catalysts reported in the literature for the dehydrogenation of bioethanol in high-value chemicals.

Remote C-H Amination and Alkylation of Camphor at C8 through Hydrogen-Atom Abstraction.

Camphor continues to serve as a versatile chiral building block for chemical synthesis. We have developed a novel method to functionalize the camphor skeleton at C8 using an intramolecular hydrogen atom abstraction. The key advance involves the use of a camphor-derived aminonitrile, which is converted to the corresponding nitrogen-centered radical under photoredox conditions to effect the 1,5-hydrogen atom transfer at C8. The resulting carbon-centered radical at C8 was utilized in a C-H amination to access topologically complex proline derivatives. Furthermore, the total synthesis of several sesquiterpenoids was accomplished by engaging the radical generated at C8 in alkylation reactions.

Optically addressable spin defects coupled to bound states in the continuum metasurfaces

Van der Waals (vdW) materials, including hexagonal boron nitride (hBN), are layered crystalline solids with appealing properties for investigating light-matter interactions at the nanoscale. hBN has emerged as a versatile building block for nanophotonic structures, and the recent identification of native optically addressable spin defects has opened up exciting possibilities in quantum technologies. However, these defects exhibit relatively low quantum efficiencies and a broad emission spectrum, limiting potential applications. Optical metasurfaces present a novel approach to boost light emission efficiency, offering remarkable control over light-matter coupling at the sub-wavelength regime. Here, we propose and realise a monolithic scalable integration between intrinsic spin defects in hBN metasurfaces and high quality (Q) factor resonances, exceeding 102, leveraging quasi-bound states in the continuum (qBICs). Coupling between defect ensembles and qBIC resonances delivers a 25-fold increase in photoluminescence intensity, accompanied by spectral narrowing to below 4 nm linewidth and increased narrowband spin-readout efficiency. Our findings demonstrate a new class of metasurfaces for spin-defect-based technologies and pave the way towards vdW-based nanophotonic devices with enhanced efficiency and sensitivity for quantum applications in imaging, sensing, and light emission.

Unlocking the potentials of Ustilago trichophora for up-cycling polyurethane-derived monomer 1,4-butanediol.

Plastic usage by microbes as a carbon source is a promising strategy to increase the recycling quota. 1,4-butanediol (BDO) is a common monomer derived from polyesters and polyurethanes. In this study, Ustilago trichophora was found to be an efficient cell-factory to valorize BDO. To investigate product formation by U. trichophora, we refined the traditional ion exclusion liquid chromatography method by examining eluent, eluent concentrations, oven temperatures, and organic modifiers to make the chromatography compatible with mass spectrometry. An LC-UV/RI-MS2 method is presented here to identify and quantify extracellular metabolites in the cell cultures. With this method, we successfully identified that U. trichophora secreted malic acid, succinic acid, erythritol, and mannitol into the culture medium. Adaptive laboratory evolution followed by medium optimization significantly improved U. trichophora growth on BDO and especially malic acid production. Overall, the carbon yield on the BDO substrate was approximately 33% malic acid. This study marks the first report of a Ustilaginaceae fungus capable of converting BDO into versatile chemical building blocks. Since U. trichophora is not genetically engineered, it is a promising microbial host to produce malic acid from BDO, thereby contributing to the development of the envisaged sustainable bioeconomy.

Bay/ortho-Octa-substituted Perylene: A Versatile Building Block toward Novel Polycyclic (Hetero)Aromatic Hydrocarbons.

ConspectusPolycyclic (hetero)aromatic hydrocarbons (PAHs) have emerged as a focal point in current interdisciplinary research, spanning the realms of chemistry, physics, and materials science. Possessing distinctive optical, electronic, and magnetic properties, these π-functional materials exhibit significant potential across diverse applications, including molecular electronic devices, organic spintronics, and biomedical functions, among others. Despite the extensive documentation of various PAHs over the decades, the efficient and precise synthesis of π-extended PAHs remains a formidable challenge, hindering their broader application. This challenge is primarily attributed to the intricate and often elusive nature of their synthesis, compounded by issues related to low solubility and unfavored stability.The development of π-building blocks that can be facilely and modularly transformed into diverse π-frameworks constitutes a potent strategy for the creation of novel PAH materials. For instance, based on the classic perylene diimide (PDI) unit, researchers such as Würthner, Wang, and Nuckolls have successfully synthesized a plethora of structurally diverse PAHs, as well as numerous other π-functional materials. However, until now the availability of such versatile building blocks is still severely limited, especially for those simultaneously having a facile preparation process, adequate solubilizing groups, favored material stability, and critically, rich possibilities for structural extension spaces.In this Account, we present an overview of our invention of a highly versatile bay-/ortho-octa-substituted perylene building block, designated as Per-4Br, for the construction of a series of novel PAH scaffolds with tailor-made structures and rich optoelectronic and magnetic properties. First, starting with a brief discussion of current challenges associated with the bottom-up synthesis of π-extended PAHs, we rationalize the key features of Per-4Br that enable facile access to new PAH molecules including its ease of large-scale preparation, favored material stability and solubility, and multiple flexible reaction sites, with a comparison to the PDI motif. Then, we showcase our rational design and sophisticated synthesis of a body of neutral or charged, closed- or open-shell, curved, or planar PAHs via controlled annulative π-extensions in different directions such as peripheral, diagonal, or multiple dimensions of the Per-4Br skeleton. In this part, the fundamental structure-property relationships between molecular conformations, electronic structures, and self-assembly behaviors of these PAHs and their unique physiochemical properties such as unusual open-shell ground states, global aromaticity, state-associated/stimuli-responsive magnetic activity, and charge transport characteristics will be emphatically elaborated. Finally, we offer our perspective on the continued advancement of π-functional materials based on Per-4Br, which, we posit, may stimulate heightened research interest in the versatile structural motifs typified by Per-4Br, consequently catalyzing further progress in the realm of organic π-functional materials.

A Boron Scan of Ethyl Acetoacetate Leads to Versatile Building Blocks.

Discovered in the 19th century, ethyl acetoacetate has been central to the development of organic chemistry, including its pedagogy and applications. In this study, we present borylated derivatives of this venerable molecule. A boron handle has been installed at either - or -position of acetoacetate by homologation of acyl-MIDA (N-methyliminodiacetic acid) boronates with diazoacetates. Either alkyl or boryl groups were found to migrate with regiochemistry being a function of the steric bulk of the diazo species. Boryl -ketoesters can be further modified into borylated pyrazolones and oximes, thereby expanding the synthetic toolkit and offering opportunities for additional modifications.

A Boron Scan of Ethyl Acetoacetate Leads to Versatile Building Blocks

AbstractDiscovered in the 19th century, ethyl acetoacetate has been central to the development of organic chemistry, including its pedagogy and applications. In this study, we present borylated derivatives of this venerable molecule. A boron handle has been installed at either ‐ or ‐position of acetoacetate by homologation of acyl‐MIDA (N‐methyliminodiacetic acid) boronates with diazoacetates. Either alkyl or boryl groups were found to migrate with regiochemistry being a function of the steric bulk of the diazo species. Boryl ‐ketoesters can be further modified into borylated pyrazolones and oximes, thereby expanding the synthetic toolkit and offering opportunities for additional modifications.

Organocatalytic Conjugate Hydroazidation and Hydrocyanation: A Metal-Free Approach to Synthetically Versatile Chiral Building Blocks

Chiral β-azido- and β-cyanocarbonyl compounds are extremely useful building blocks in asymmetric synthesis, thanks to the manyfold reactivity of their functional groups. The enantioselective synthesis of such compounds, until the beginning of the 21st century, has been mostly achieved using transition-metal chiral catalysts. The explosion of enantioselective organocatalysis, however, has enabled the development of efficient metal-free methodologies with significant benefits in terms of costs and environmental safety. An overview of the advances made in recent years in this field is herein presented.

Cooperative Fe/Co-Catalyzed Remote Desaturation for the Synthesis of Unsaturated Amide Derivatives.

Unsaturated amides represent common functional groups found in natural products and bioactive molecules and serve as versatile synthetic building blocks. Here, we report an iron(II)/cobalt(II) dual catalytic system for the syntheses of distally unsaturated amide derivatives. The transformation proceeds through an iron nitrenoid-mediated 1,5-hydrogen atom transfer (1,5-HAT) mechanism. Subsequently, the radical intermediate undergoes hydrogen atom abstraction from vicinal methylene by a cobaloxime catalyst, efficiently yielding β,γ- or γ,δ-unsaturated amide derivatives under mild conditions. The efficiency of Co-mediated HAT can be tuned by varying different auxiliaries, highlighting the generality of this protocol. Remarkably, this desaturation protocol is also amenable to practical scalability, enabling the synthesis of unsaturated carbamates and ureas, which can be readily converted into various valuable molecules.

Application of the LADA Strategy for the Synthesis of Unnatural Amino Acids through 1,2-Aryl Migration of Allylic Alcohols.

Unnatural amino acids are versatile building blocks. Herein, we report the application of the LADA strategy for the direct synthesis of unnatural amino acids through 1,2-aryl migration of allylic alcohols. This reaction proceeds under mild conditions, tolerates diverse functionalities, and works smoothly on different thiols.

Recent Advances in the Multicomponent Synthesis of Heterocycles Using 5-Aminotetrazole

AbstractThe unique reactivity and beneficial features of the 5-aminotetrazole synthon (1H-tetrazol-5-amine) have made it a versatile and effective building block in the synthesis of heterocyclic compounds. In addition, several drugs containing this scaffold with a wide array of biological properties have been already introduced. Heterocyclic structures are the backbone of many biologically active and industrially important compounds. 5-Aminotetrazole is one of the favored synthons used in the preparation of heterocycle-bearing compounds, especially in multicomponent synthesis. This review highlights a comprehensive overview of the emerging applications of 5-aminotetrazole as a key component in the synthesis of heterocyclic frameworks through multicomponent reactions, reported between 2017 and July 2023.1 Introduction2 5-Aminotetrazole3 Tetrazolopyrimidine Compounds4 Spiro Compounds5 Miscellaneous6 Conclusion

Continuous Flow Synthesis of Nitrosoarenes via Photochemical Rearrangement of Aryl Imines.

Nitrosoarenes are versatile organic building blocks; however, their intrinsic instability and limited synthetic accessibility have so far restricted their widespread use. Herein, we present a new continuous flow route toward these entities that is based on a direct photochemical rearrangement process using o-nitrophenylimines as starting materials. Due to the underlying redox mechanism, a new amide group accompanies the formation of the nitroso group. Crucial to the success of this approach is the use of trifluoroethanol as a solvent and high-power light-emitting diodes (365 nm) as light sources that provide uniform irradiation and high efficiency of the resulting continuous flow method. The process is fast and robust, with high functional group tolerance and high throughput. The formation of the nitroso moiety is supported by full spectroscopic analysis, including X-ray crystallography. The scalability of this flow approach allows access to gram quantities of nitroso species for which we highlight a small set of derivatization reactions underlining their synthetic utility.

Synthesis of Perfluoro Alkyl/Alkenyl Aryl Sulfide: C−S Coupling Reaction Using Hexafluoropropylene Dimer (HFPD) as a Building Block

AbstractEfficient approaches to perfluoroalkyl/alkenyl aryl sulfides were accomplished by a C−S coupling reaction under mild conditions. Hexafluoropropylene dimer was employed as a versatile building block for the perfluoroalkylation and perfluoroalkenylation of thiophenol. The application of the synthetic strategy was demonstrated by the high‐yield transformation of a broad range of aryl derivatives. A plausible mechanistic explanation was proposed to elaborate the differences between the two reaction pathways. The methodology provides straightforward and convenient access to aryl sulfides constituting C6 perfluoroalkyl and perfluoroalkenyl substituents.

Chiral Isochalcogenourea-Catalysed Enantioselective (4+2) Cycloadditions of Allenoates.

Allenoates are versatile building blocks which are primarily activated and controlled using chiral tert. phosphine and tert. amine Lewis bases. We herein report the first example of allenoate activation by using chiral isochalcogenoureas (IChU) for formal (4+2) cycloaddition reactions. Compared to established phosphine and amine catalysis, the use of these easily available Lewis bases enables new stereoselective reaction pathways proceeding with high enantioselectivities, diastereoselectivities, and in good yields. In addition, the factors governing enantioselectivity and the origin of the observed differences compared to other commonly used Lewis bases are explained.

Chiral Isochalcogenourea-Catalysed Enantioselective (4+2) Cycloadditions of Allenoates.

Allenoates are versatile building blocks which are primarily activated and controlled using chiral tert. phosphine and tert. amine Lewis bases. We herein report the first example of allenoate activation by using chiral isochalcogenoureas (IChU) for formal (4+2) cycloaddition reactions. Compared to established phosphine and amine catalysis, the use of these easily available Lewis bases enables new stereoselective reaction pathways proceeding with high enantioselectivities, diastereoselectivities, and in good yields. In addition, the factors governing enantioselectivity and the origin of the observed differences compared to other commonly used Lewis bases are explained.