Tertiary Carbon Research Articles

Asymmetric α‐Azidation Reaction of β‐Ketoesters Catalyzed by Chiral Tin Alkoxides

AbstractA catalytic enantioselective α‐azidation reaction of β‐ketoesters with an azidated hypervalent iodine reagent was achieved by using an (R)‐BINOL‐derived chiral tin dibromide possessing 4‐t‐butylphenyl groups at the 3‐ and 3’‐positions as the chiral precatalyst in the presence of sodium ethoxide and ethanol. Optically active α‐azido‐β‐ketoesters having a chiral tertiary carbon were obtained in moderate to high yields under the influence of the chiral tin diethoxide generated in situ.

Synthesis of Quaternary and Tertiary Carbon‐Substituted Arenes by Lewis Base Promoted Site‐Selective Coupling with Allylic Nucleophiles

AbstractA practical method for the preparation of quaternary and tertiary allyl‐substituted heteroarenes by site‐selective couplings of heteroaryl nitriles and allylic nucleophiles is disclosed. Transformations utilize readily accessible stable reagents, proceed in the presence of a Lewis base activator, and undergo aryl‐C(sp3) quaternary and tertiary carbon formation with high γ‐selectivity (up to >98 : 2 γ : α).

Synthesis of Quaternary and Tertiary Carbon-Substituted Arenes by Lewis Base Promoted Site-Selective Coupling with Allylic Nucleophiles.

A practical method for the preparation of quaternary and tertiary allyl-substituted heteroarenes by site-selective couplings of heteroaryl nitriles and allylic nucleophiles is disclosed. Transformations utilize readily accessible stable reagents, proceed in the presence of a Lewis base activator, and undergo aryl-C(sp3 ) quaternary and tertiary carbon formation with high γ-selectivity (up to >98 : 2 γ : α).

Daily Monitoring at a Full-Scale Wastewater Treatment Plant Reveals Temporally Variable Micropollutant Biotransformations.

Despite decades of micropollutant (MP) monitoring at wastewater treatment plants (WWTPs), we lack a fundamental understanding of the time-varying metabolic processes driving MP biotransformations. To address this knowledge gap, we collected 24-h composite samples from the influent and effluent of the conventional activated sludge (CAS) process at a WWTP over 14 consecutive days. We used liquid chromatography and high-resolution mass spectrometry to (i) quantify 184 MPs in the influent and effluent of the CAS process; (ii) characterize temporal dynamics of MP removal and biotransformation rate constants; and (iii) discover biotransformations linked to temporally variable MP biotransformation rate constants. We measured 120 MPs in at least one sample and 66 MPs in every sample. There were 24 MPs exhibiting temporally variable removal throughout the sampling campaign. We used hierarchical clustering analysis to reveal four temporal trends in biotransformation rate constants and found MPs with specific structural features co-located in the four clusters. We screened our HRMS acquisitions for evidence of specific biotransformations linked to structural features among the 24 MPs. Our analyses reveal that alcohol oxidations, monohydroxylations at secondary or tertiary aliphatic carbons, dihydroxylations of vic-unsubstituted rings, and monohydroxylations at unsubstituted rings are biotransformations that exhibit variability on daily timescales.

Ni/HZSM-5 catalysts for hydrodeoxygenation of polycarbonate plastic wastes into cycloalkanes for sustainable aviation fuels

Hydrodeoxygenation (HDO) is one of the effective methods for upcycling polycarbonate (PC) plastic waste, but the development of low-cost, high-performance HDO catalysts still faces great challenges. In this work, we report that a bifunctional Ni/HZSM-5 catalyst can directly upgrade PC plastic wastes into sustainable aviation fuel ranged cycloalkanes in high yields (99.3 %) with 81.2 % yield of C15 dicycloalkane under mild reaction conditions (190 °C, 4 MPa H2). Controlled reactions of PC and probe molecules demonstrated the conversion of PC into C15 dicycloalkanes involves PC depolymerization by direct cleavage of C-O bonds adjacent to benzene ring and ester group, forming C15 aromatics and C15 monophenols at the metal sites, followed by hydrogenation of C15 aromatics rings on metallic Ni sites and HDO of C15 monophenols on metal-acid dual sites parallel to generate C15 dicycloalkane. The C-C cracking mainly occurred on the tertiary carbon adjacent to the benzene ring on acidic sites of HZSM-5, thus forming C6∼C9 monocyclic alkanes. The realization of this process can be attributed to the cooperation between metal sites and acid centers on Ni/HZSM-5. Besides, the metal-acid balance (MAB) in Ni/HZSM-5 significantly affected the HDO activity and product distribution. 20Ni/HZSM-5(200) with suitable MAB showed good HDO activity and excellent selectivity to C15 dicycloalkane. In addition, the obtained catalyst was also capable of converting common real PC plastics wastes (CD disk, DVD disk and PC sheet) into cycloalkanes with the yield up to 98 % and exhibited excellent stability. This approach to construct inexpensive bifunctional catalysts highlights an efficient and reliable route for HDO of PC to sustainable aviation fuel, providing a new avenue towards a circular economy.

Synthesis of Aliphatic Nitriles via Desulfonylative Smiles Rearrangement

AbstractHerein, we demonstrate the synthesis of aliphatic nitriles from N-acyl (2-nitrophenyl)sulfonamides via a desulfonylative Smiles rearrangement. The developed reaction routes provide a variety of aliphatic nitriles containing primary, secondary, and tertiary carbon centers in good-to-excellent yields. Our method requires the use of the easy-to-handle reagent potassium acetate and solvent 1,3-dimethyl-2-imidazolidinone, and it does not rely on toxic metal cyanides or transition metals. The process is suitable for large-scale reaction and for one-pot syntheses starting from an acyl chloride or a carboxylic acid.

Investigating the influence of plastic waste oils and acetone blends on diesel engine combustion, pollutants, morphological and size particles: Dehalogenation and catalytic pyrolysis of plastic waste

Most research into the treats of plastic wastes have concentrated mainly on single-exposure pathways or products. These practices fail to acknowledge that the complications of carbon particles from engines are produced not only by diesel but by any plastic oils due to the vast amount of contaminants. With the potential to significantly weaken the impact of contaminants, the present study investigates the effects of dehalogenation and catalytic pyrolysis on plastic waste, as well as the risks associated with plastic oil blends on diesel engine. Different types of washing were conducted to effectively dehalogenate plastic waste. After pretreatment, odor compounds were analyzed using GC–MS. Subsequently, various types of pretreated plastic samples underwent catalytic pyrolysis with a 5:1 ratio of HDPE to Al2O3·2SiO2·2H2O. Differences in physico-chemical properties and hydrocarbon compounds of oils were determined. Experiments were performed using different fuel blends in a diesel engine under steady-state conditions, and their effects on combustion, emissions, morphology, and size particles were analyzed. The results show that sample B exhibited a lower toxicity level of 1,3-butadiene compared to other samples, while acetone and terpenes represented the second and third-highest emission levels in flakes, respectively. Sample C started to degrade at low temperatures (<300 °C) due to carbon addition from ethyl acetate solvent into the tertiary carbon chain of the flakes. DAP3 fuel achieved a higher reaction due to its degree of unsaturation and lower viscosity, resulting in the formation of smaller fuel droplets at high injection pressure and heat release rate (HRR). Higher emission levels were observed by DAP1 and D100, exceeding the Euro 5/6 standard limits. However, DAP3 fuel resulted in an average reduction of ∼17.14% and 21.86% in CO and smoke emissions, respectively, accompanied by a slight decrease in NOx and HC levels. Conversely, there were inconsistencies in the emission results observed with DAP2. Compared to D100, both DAP1 and DAP2 exhibited a significant accumulation and coarse particles in the PM10 forms at a peak of ∼83 nm. Whereas the DAP3 showed a smaller mobility Dp with a low nucleation particle peak, which was prone to absorb the unburned HC soot and later change to accumulation mode particles.

Ruthenium deposited onto graphitic carbon modified with boron for the intensified photocatalytic production of benzaldehyde

The selective oxidation of added-value aromatic alcohols into aldehydes of high interest via photocatalysis has been postulated as a green and competitive oxidative reaction at mild conditions. This work is focused on the design of a tertiary graphitic carbon nitride (g-C3N4) based photocatalysts competitive for the photocatalytic production of benzaldehyde in an aqueous solution. The polymeric g-C3N4 has been modified in an easy one-pot green synthesis scheme, with the incorporation of boron in the polymeric structure and the deposition of ruthenium nanoparticles. The Ru ratio within 0.5–4% was assessed. The photocatalysts were fully characterized (XRD, FTIR, XPS, N2 isotherms, DRS-UV–visible, and PL) and the photocatalytic activity was assessed in the oxidation of benzyl alcohol to benzaldehyde in an aqueous solution. The incorporation of boron enhanced the selectivity towards benzaldehyde due to enhanced separation charges suggested by the photoluminescence technique; whereas ruthenium improved the reaction rate of the alcohol, affecting negatively the selectivity though. The sample containing 1% of Ru was selected as the optimum in terms of selectivity. The relative contribution of the involved reactive oxidant species was assessed by chemical scavenger tests, highlighting the contribution of the photo-generated holes followed by O2•‾. The analysis of the band’s alignment of the g-C3N4 before the modification with boron and ruthenium supports the enhancement by rising the redox potential of the holes released in the valence band.

Deconvoluting the roles of polyolefin branching and unsaturation on depolymerization reactions over acid catalysts

Developing a circular economy for plastics is a societal priority with a range of stakeholders engaged in developing pathways to mechanical and chemical recycling. Acid catalysis has been proposed as an attractive strategy to chemically recycle or upcycle plastic waste. In principle, the energetics that govern polyolefin decomposition reactions over Brønsted acid sites should be the same ones known for alkane cracking. However, the nature of polymers as feedstock imposes new challenges for these well-known processes, e.g., strong mass transfer limitations. To better understand the role of polymer structure and diffusion on cracking rates, the effect of tertiary carbons, chain unsaturation, and catalyst active sites distribution were studied. Our findings confirm that higher concentrations of tertiary carbons will govern decomposition reactions, regardless of diffusion limitations. Also, we unveil that LLDPE reactions mostly take place on the external surface of ZSM-5 crystals while HDPE conversion takes place within the zeolite pores.

Fe-Catalyzed Regioselective C(sp3)–H-Abstraction by Tertiary Cyclopropyl Radicals

Tertiary carbon radicals are usually more stable than secondary carbon radicals, and the hydrogen atom transfer (HAT) from secondary C(sp3)–H bonds to tertiary carbon radicals is normally considered to be a thermodynamically disfavored pathway. Herein, we disclose an unusual protocol involving a C(sp3)–H functionalization enabled by a tertiary cyclopropyl radical and proceeding through hydrogen abstraction from a variety of secondary and tertiary aliphatic C(sp3)–H bonds. The reaction can furnish valuable, densely functionalized cyclopropane derivatives. Sufficient mechanistic experiments and density functional theory (DFT) calculations have provided theoretical insights into the chemo- and regioselectivity in this underexplored HAT protocol. The method features broad functional group compatibility and high product diversity and offers a new prospect for radical C(sp3)–H functionalization.

Fluorination of the tertiary carbon at the edge of graphene oxide

Fluorination of the tertiary carbon at the edge of graphene oxide

Asymmetric Mannich reaction of N-Boc aminosulfones with 3-methylbenzofuran-2 (3H) - Ones catalyzed by a chiral phase-transfer catalyst

An enantioselective Mannich reaction of N-Boc aminosulfones with 3-methylbenzofuran-2 (3H)-ones catalyzed by a quinine-derived bifunctional phase transfer catalyst was developed, by which a series of chiral benzofuranones bearing adjacent quaternary and tertiary carbon centers were obtained in high yields (up to 96%) with good diastereoselectivities (up to >99:1) and enantioselectivities (up to 98%).

Theoretical study on the reaction mechanism of a new XLPE insulation material without cross‐linking byproducts: An alternative to peroxide cross‐linking

AbstractObjectiveDesign a new cross‐linked polyethylene (XLPE) insulation material without cross‐linking by‐products (an alternative to peroxide cross‐linking). Investigate the process of covalent bonds forming and reaction mechanism of four reaction systems.MethodTheoretical calculation of the reaction potential energy information of the eleven reaction channels is used density functional theory at B3LYP/6‐311+G(d,p) level.ResultsThe calculation results show that the epoxy and reactive functional groups between two poly‐ethylene copolymers can react in situ, form covalent bonds, and realize a network XLPE. This reaction process is cross‐linking byproduct‐free. The reactivity of carboxylic acid functional group is stronger among four reaction systems considered.DiscussionThe reaction Gibbs energy barriers of synergistic reaction are lower than that of step by step reaction. The reaction channel of attacking tertiary carbon site CH on epoxy is more kinetically favorable than that of attacking secondary carbon site CH2 on epoxy.ConclusionThe cross‐linking of epoxy and reactive functional groups between two polyethylene copolymers in situ would be beneficial to avoid forming cross‐linking byproducts of peroxide cross‐linking process, which is a promising method for design thermoplastic insulation materials for power cables.

Polymerization of Allyltrimethylisilane and 4-Methyl-1-Pentene by Using Metallocene Catalysts.

Polymers of higher olefin, obtained by Ziegler-type polymerization, have been used in some critical fields, e.g., as the membrane for extracorporeal membrane oxygenation (ECMO), which plays an important role in the treatment of patients with severe COVID-19. The polymer obtained by a single-site catalyst, e.g., metallocene catalysts, demonstrated a higher performance. The homo- and co-polymerization of allyltrimethylisilane (ATMS) and 4-methyl-1-pentene (4M1P) were conducted using syndiospecific (cat 1) and isospecific (cat 2) metallocene catalysts. Cat 1 showed low conversions and provided a polymer with a higher molecular weight, while cat 2 behaved oppositely. 13C-NMR spectra certified the stereotacticity of the resultant polymer, and the resonance of the carbon atom of CH2 (αα') between the two tertiary carbon atoms of the ATMS and 4M1P units were observed. This could be the evidence of the formation of a true copolymer. The crystallization of the polymer was explored using a differential scanning calorimeter (DSC) and wide angle X-ray diffraction (WAXD). All homopolymers and some of the copolymers showed high melting temperatures and low melting enthalpies. The WAXD patterns of the syndiotactic polymer and isotactic homopolymer or the ATMS-rich copolymer were consistent with the reported literature, but the isotactic 4M1P-rich copolymer provided the crystal form I, which is unusual for a 4M1P polymer without any pretreatment.

Interaction between Divalent Copper Fluoride and Carboxamide Group Enabling Stereoretentive Fluorination of Tertiary Alkyl Halides

AbstractHerein, we report a copper‐catalyzed stereospecific fluorination involving CsF and α‐bromocarboxamides as tertiary alkyl sources that, unlike traditional stereospecific routes involving stereoinversive SN2 reactions, proceeds with retention of stereochemistry. The developed stereospecific Cu‐catalyzed reaction is among the most efficient methods for synthesizing fluorinated molecules that possess highly congested stereogenic carbon centers. Mechanistic studies revealed that the combined reactivity of CuF2 and Cs salt is essential for completing the catalytic cycle. Our catalytic system underwent fluorination exclusively with tertiary alkyl bromides and did not react with primary alkyl bromides, indicating that this stereospecific fluorination methodology is suitable for synthesizing fluorinated building blocks possessing stereo‐defined F‐containing tertiary carbon stereogenic center.

Interaction between Divalent Copper Fluoride and Carboxamide Group Enabling Stereoretentive Fluorination of Tertiary Alkyl Halides.

Herein, we report Cu-catalyzed stereospecific fluorination involving CsF and α-bromocarboxamides as tertiary alkyl sources that, unlike traditional stereospecific routes involving stereoinversive SN2 reactions, proceeds with retention of stereochemistry. The developed stereospecific Cu-catalyzed reaction is among the most efficient methods for synthesizing fluorinated molecules that possess highly congested stereogenic carbon centers. Mechanistic studies revealed that the combined reactivity of CuF2 and Cs salt is essential for completing the catalytic cycle. Our catalytic system underwent fluorination exclusively with tertiary alkyl bromides and did not react with primary alkyl bromides, indicating that this stereospecific fluorination methodology is suitable for synthesizingfluorinated building blocks possessing stereo-defined F-containing tertiary carbon stereogenic center.

Abstraction and addition reactions of four γ‐lactones with H‐atoms and methyl radicals

AbstractThe five‐membered cyclic esters, or γ‐lactones, are promising candidates as biofuel additives and green solvent components. A comprehensive study of thermochemical and kinetic properties of γ‐butyrolactone (GBL), γ‐valerolactone (GVL), γ‐caprolactone (GCL), and γ‐heptalactone (GHL) has been conducted. The entropy, , specific heat, , enthalpy function, , and the enthalphy of formation at 298.15 K, , as well as the adiabatic ionization potential and single bond dissociation energies are reported. Bimolecular rate constants for the abstraction of H‐atom by H• and CH are presented on a per abstractable hydrogen basis; abstraction at the tertiary carbon site is consistently favored, while abstraction by CH lags behind H•. Addition reactions of H• and CH have high barriers and favor addition to the C‐center.

Enantioselective and stereodivergent hydromonofluoroalkylation of conjugated and remote dienes

Because of the widespread applications of optically active alkyl fluorides in medicinal and agro chemicals, enantioselective and even stereodivergent construction of alkyl fluorides remains highly desirable but underdeveloped. Transition-metal-catalyzed asymmetric hydrofluoroalkylation of readily available dienes represents a novel route to achieve this goal, yet receives scarce study. Here we report an intriguing palladium-catalyzed enantioselective hydromonofluoroalkylation reaction of conjugated dienes. Both monosubstituted and internal dienes proceed well with the transformation and furnish alkyl fluorides in generally >80% yield and >90% ee. A stereodivergent hydromonofluoroalkylation protocol via Pd/Cu co-catalysis is also established for the access to all four stereoisomers of corresponding moieties bearing a fully-substituted F-stereogenic center and vicinal tertiary carbon center. In addition, asymmetric migratory hydromonofluoroalkylation of skipped dienes is developed to realize the direct allylic CH fluoroalkylation. A compound library of enantioenriched cyclic fluorides is thus built to highlight the transformation potential of present methodology.

A Mechanistically Deceiving Formation of Aryl(1-indanyl)ketones via Acid-Catalyzed Cyclization of ortho-Alkynylarylmethanols.

The generation of reactive carbocation intermediates from ortho-alkynylarylmethanol substrates was utilized as a means for the synthesis of aryl(1-indanyl)ketones . Substrates with a tertiary carbon at the β-position to the arene generated a carbocation intermediate via dehydration/protonation, followed by cyclization and hydration to give indanylketone products. For substrates with a quaternary carbon at that position, a carbocation intermediate was generated by protonation/elimination of water, followed by a 1,2-shift and a subsequent cyclization/hydration to give highly substituted indanylketones.

Chiral Phosphine Catalyzed Allylic Alkylation of Benzylidene Succinimides with Morita–Baylis–Hillman Carbonates

Owing to their unique chemical properties, α-alkylidene succinimides generally act as versatile synthons in organic synthesis. Compared with well-established annulations, nucleophilic alkylations of α-alkylidene succinimides are very limited. Accordingly, an organocatalytic allylic alkylation of α-benzylidene succinimides with Morita-Baylis-Hillman (MBH) carbonates was established. In the presence of a chiral phosphine catalyst, α-benzylidene succinimides reacted smoothly with MBH carbonates under mild conditions to furnish a series of optical active succinimides in high yields and enantioselectivities. Different from the reported results, the organocatalytic enantioselective construction of pyrrolidine-2,5-dione frameworks bearing contiguous chiral tertiary carbon centers was achieved via this synthetic strategy. Scaling up the reaction indicated that it is a practical strategy for the organocatalytic enantioselective alkylation of α-alkylidene succinimides. A possible reaction mechanism was also proposed.