Reactivity Of Carbon Research Articles

Synthesis of amphiphilic asymmetrical dithienylethenes with aryl groups at the reactive carbons

A synthetic route for the preparation of amphiphilic asymmetrical dithienylethenes that incorporate methyl groups at the 4- and 4′-positions and an aryl group at one of the reactive carbons has been developed. The presence of a bulky aryl substituent ensures a relatively large change in molecular geometry upon photoisomerization, whereas the presence of methyl groups provide enhanced photostability. Notably, a substituent effect was systematically revealed en route to the preparation of the dithienylethene precursors. In particular, this formal substitution reaction was significantly inhibited due to steric hindrance, stemming from the presence of aryl and methyl groups at the alpha positions of the preformed thienyl carbanionic carbon, and an aryl group on the monosubstituted perfluorocyclopentene derivative.

Influencing factors of the explosion characteristics of modified coal used for blast furnace injection

An in-depth investigation and accurate analysis of the blast furnace injection fuel explosion characteristics is important since it is a crucial factor affecting ironmaking safety, cost reduction, and rational use of coal resources. This current study investigated explosion characteristics, morphology, pore distributions, and carbon structure of modified coal. The results showed that although the volatile matter content of modified coal was similar to the anthracite coal, the explosiveness of the modified coal was stronger than the high-volatile raw coal and the bituminous coal at various oxygen concentrations. The specific surface area of modified coal was 271.5 m2/g and pores were well developed. This provided good kinetic conditions for oxygen molecules to diffuse into the particle's surface and interior. The lower graphitized carbon structure of modified coal had high carbon reactivity, which improved the explosion performance. The strong explosiveness of the modified coal was not attributed to the cracking and the combustion of volatile matter. The ID/IG value (the intensity ratio of the D band and G band) was considered an important factor for evaluating the explosion characteristics of the samples.

Experimental Investigation of the Interaction between a Phosphate Ester Scale Inhibitor and Carbonate Rocks for Application in Squeeze Treatments

Studying the interaction between scale inhibitors (SIs) and chemically reactive carbonate minerals is crucial for determining SI retention in “squeeze” treatments. This study investigated the reten...

Carbon deposition in porous nickel/yttria-stabilized zirconia anode under methane atmosphere

A commercial solid oxide fuel cell with a Ni/YSZ anode was characterized under a pure methane atmosphere. The amount of deposited carbon increased with an increase in temperature but decreased when the temperature exceeded 700°C. The reactivity of carbon decreased with increasing deposition temperature. Filamentous carbon was deposited from 400 to 600°C, whereas flake carbon was deposited at 700 and 800°C. With increasing temperature, the intensity ratio of the D band over the sum of the G and D bands was constant at the beginning and then decreased with the transformation of the carbon morphology. The crystallite size increased from 2.9 to 13 nm with increasing temperature. The results also indicated that the structure of the deposited carbon was better ordered with increasing deposition temperature. In comparison with pure Ni powders, the interaction between the YSZ substrate and Ni particles could not only modify the carbon deposition kinetics but also reduce the temperature effect on the structure and reactivity variation of carbon.

Role of reactive oxygen species in As(III) oxidation by carbonate structural Fe(II): A surface-mediated pathway

Arsenite oxidation is commonly found during the removal of arsenite by iron minerals. The influencing factors and mechanisms of As(III) oxidation in reactive carbonate structural Fe(II) (CSF) suspensions were investigated in this study. Results showed that oxidation efficiency of As(III) was susceptible to CSF dosage, initial pH and dissolved oxygen (DO). It is interesting to note that the presence of iodide could conspicuously facilitate the oxidation efficiency of As(III) by accelerating Fe(III)/Fe(II) cycle. Scavenging experiments demonstrated that H2O2 and ·O2– were the crucial ROSs in the pH range of 5.0–9.0. Besides, the other predominant ROSs accounting for As(III) oxidation were Fe(IV) and surface-bound hydroxyl radical (·OH) in acid and neutral solutions while Fe(IV) became the main oxidant in alkaline solutions. Production of ROSs was attributed to the oxygenation of Fe2+ adsorbed on Fe(III) oxyhydroxides and complexed Fe(II) under neutral condition. No ROSs could be examined in the liquid phase, a surface-mediated mechanism was thus proposed: ROSs were generated on the surface of CSF while As(III) was adsorbed on the surface of CSF and then oxidized to As(V) by surface-bound ROSs. This study may shed light on molecular oxygen activation mechanism by carbonate structural Fe(II) during arsenite oxidation.

Oxygen vacancy associated single-electron transfer for photofixation of CO2 to long-chain chemicals

The photofixation and utilization of CO2 via single-electron mechanism is considered to be a clean and green way to produce high-value-added commodity chemicals with long carbon chains. However, this topic has not been fully explored for the highly negative reduction potential in the formation of reactive carbonate radical. Herein, by taking Bi2O3 nanosheets as a model system, we illustrate that oxygen vacancies confined in atomic layers can lower the adsorption energy of CO2 on the reactive sites, and thus activate CO2 by single-electron transfer in mild conditions. As demonstrated, Bi2O3 nanosheets with rich oxygen vacancies show enhanced generation of •CO2– species during the reaction process and achieve a high conversion yield of dimethyl carbonate (DMC) with nearly 100% selectivity in the presence of methanol. This study establishes a practical way for the photofixation of CO2 to long-chain chemicals via defect engineering.

Synthesis and graphitization of resole resins by ferrocene

Commercial (Rs) and laboratory synthesized resoles (LSRs) containing 3–5 wt% ferrocene have been used to study the development of thermosetting resin compositions as binder materials for carbon-containing refractories (CCRs) production. The LSRs were developed based on formaldehyde to phenol 1.5 mol.% (1.5Rs) and 2.0 mol.% (2Rs). Microstructure and oxidation resistance of carbons derived from plain and modified resins have been compared. Chemical structure of the resins was studied using Fourier Transform InfraRed-Attenuated Total Reflection (FTIR-ATR) spectroscopy. X-ray Photoelectron spectroscopy was used to examine chemical changes during heat treatment of the modified products. Flow behavior of plain and formulated resins has been measured under isothermal condition. Rheology measurement results show that the selected amount of ferrocene did not affect the resin near-Newtonian fluid behavior and processability during refractory production. X-ray diffraction (XRD) analysis and transmission Electron Microscope (TEM) were used to characterize the derived carbon samples after thermal treatment of the resins. The results demonstrate that ferrocene is an excellent additive for crystallizing resoles carbon. The presence of fringes in TEM images indicates the graphitized carbon microstructure. The carbon reactivity in an oxidizing environment was also determined via thermogravimetric analyzer (TGA). Several factors, such as bond strength and atoms arrangement, have been found to control the carbonized modified-resin oxidation resistance.

Synthesis of UV and thermal dual curing oligomer for solder resist ink using ink‐jet printing

ABSTRACTA novel solder resist ink for inkjet printing containing the ultraviolet (UV) and thermal dual curing oligomer is introduced in this work. Three kinds of acrylic monomers for the synthesis of the oligomer are successful prepared and their structures are determined by Fourier transfer infrared. Both UV curing process and thermostability are monitored under UV differential scanning calorimetry and thermogravimetric analysis. For the photoreaction process, the oligomer using Lauryl methacrylate as the material of copolymerization possesses the highest reactivity and conversion of carbon–carbon double bond. Besides, this kind of oligomer also owns excellent thermostability, just losing 5.9% of its weight at 288 °C. The solder resist inks containing the oligomers and jetting by the inkjet printer are tested with the adhesion, soldering resistance, and other performances, presenting the outstanding heat resistance and wide application prospects. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47428.

Two Metrics Describing the Causes of Seasonal and Spatial Changes in Subglacial Aqueous Chemistry

Seasonal change in surface melt input and spatial controls on the distribution of subglacial water can cause considerable variability in the aqueous chemistry of subglacial waters. Much of this variability has been interpreted in terms of a single variable: water residence time, with slow flow assumed to correlate with greater mineral dissolution and oxidative weathering. We synthesize data from a range of glacier and ice sheet settings to show that this approach does not adequately describe presently available data. Instead, we propose that two independent variables control spatial and seasonal changes in aqueous chemistry in subglacial settings: atmospheric gas abundance and sediment supply abundance. Where atmospheric gases are abundant, carbonation weathering is responsible for most of the subglacial chemical activity; where they become limited, oxidation weathering becomes more dominant. Where freshly comminuted sediment is abundant, easily dissolved minerals, especially calcite, have proportionally more influence on subglacial hydrochemistry; where sediment supply is limited, silicate minerals and less reactive carbonate minerals will increase in relative influence. In most settings, simple metrics of the abundance of SO42- and Ca2+ in the subglacial waters can characterize these two variables. In the data we synthesize, neither variable consistently correlates to the inferred water residence time, nor do the variables consistently correlate with each other. Spatial data show that point locations and small catchments on the glacial bed differ substantially from the integrated composition found at glacial outlets. The varied response in the subglacial aqueous chemistry to changing water residence times suggests complex control by a broad range of glaciological factors that affect water routing and subglacial sediment generation.

The role of reactive oxygen species and carbonate radical in oxcarbazepine degradation via UV, UV/H2O2: Kinetics, mechanisms and toxicity evaluation

Oxcarbazepine (OXC) is ubiquitous in the aqueous environment. And due to its ecotoxicological effects and potential risks to human, an effective way to eliminate OXC from aqueous environment has aroused public concerns in recent years. Radical-based reactions have been shown to be an efficient way for OXC destruction, but the reactions of OXC with reactive oxygen species (ROS) and carbonate radical (CO3•−) are still unclear. In this study, we focused the degradation of OXC and ROS, CO3•− generation mechanism, and their roles in OXC degradation via UV and UV/H2O2. The triplet state of oxcarbazepine (3OXC∗) was found to play an important role in OXC degradation via UV. And hydroxyl radicals (•OH) and singlet oxygen (1O2) were found to be the dominant ROS in OXC degradation. Superoxide radical (O2•−) did not react with OXC directly, but it may react with intermediate byproducts. Generation of CO3•− played a positive role on OXC degradation for both UV and UV/H2O2. In addition to •OH, 3OXC* also contribute to CO3•− production. The second-order rate constants of OXC with •OH and CO3•− were 1.7 × 1010 M−1 s−1 and 8.6 × 107 M−1 s−1, respectively. Potential OXC degradation mechanisms by •OH were proposed and included hydroxylation, α-ketol rearrangement, and benzylic acid rearrangement. Compared with non-selective •OH, the reactions involving CO3•− are mainly electron transfer and hydrogen abstraction. And the acute toxicity of OXC was lower after UV/H2O2 and UV/H2O2/HCO3− treatments, which was confirmed by luminescent bacterial assay (Vibrio fischeri bacterium).

Liquid-phase oxidation of cyclohexane. Elementary steps in the developed process, reactivity, catalysis, and problems of conversion and selectivity

The literature data concerning features of the kinetics and mechanisms of elementary steps of liquid-phase oxidation of cyclohexane and its oxygen derivatives are considered and analyzed. A comparison of rates of intermolecular and intramolecular reactions of cyclohexylperoxyl radicals under the industrial conditions indicated a necessity to take into account intramolecular interactions. The occurrence of cross recombination of hydroperoxyl and α-hydroxyperoxyl radicals without chain termination in the course of cyclohexanol and 2-hydroxycyclohexanol oxidation was proved. A significance of degenerate branching reactions involving cyclohexyl hydroperoxide in the industrial process of cyclohexane oxidation at 423 K was evaluated. The influence of the electron-withdrawing functional groups on the reactivity of carbon–hydrogen bonds of organic compounds in the reactions with electrophilic peroxyl radicals was studied. The low conversion of a substrate in the industrial process are mainly caused by the radicalchain oxidation of cyclohexanone leading only to by-products. The catalysts of cyclohexane oxidation, viz., compounds of variable valence metals, affect the reaction rate and ratio of the yields of the target products (cyclohexyl hydroperoxide, cyclohexanol, and cyclohexanone) but exert no effect on their relative reactivity. The use of the catalytic additives increasing the yield of cyclohexanone in the step of cyclohexane oxidation in the production of caprolactam is revealed to be inexpedient.

Effect of very high limestone content and quality on the sulfate resistance of blended cements

Sulfate attack was investigated on blended ordinary Portland cement (OPC) based mortars with limestone replacements up to 65 wt-% in 30 g·L−1 Na2SO4 solutions at 20 °C and 8 °C for 200 days. Although CEM I 52.5R with ∼12 wt-% C3A was used, some blended mortars with a water/powder ratio of 0.35 and ≤50 wt-% limestone replacement passed the test requirements (Δ-expansion ≤0.5 mm/m after 91 days) and exhibited a better performance than pure OPC reference mixes with water/powder ratios of 0.5 and 0.6. Under accelerated test conditions, the deterioration level of blended mortars arising from sulfate attack can be approximated by the reaction of portlandite with aqueous sulfate to secondary expansive gypsum, ettringite and thaumasite. The pore structure and the reactivity of carbonates and cement hydrates originally present in blended cements should be considered for predicting the long-term stability of concrete in sulfate-loaded environments.

Reactivity of Amorphous Carbon Surfaces: Rationalizing the Role of Structural Motifs in Functionalization Using Machine Learning.

Systematic atomistic studies of surface reactivity for amorphous materials have not been possible in the past because of the complexity of these materials and the lack of the computer power necessary to draw representative statistics. With the emergence and popularization of machine learning (ML) approaches in materials science, systematic (and accurate) studies of the surface chemistry of disordered materials are now coming within reach. In this paper, we show how the reactivity of amorphous carbon (a-C) surfaces can be systematically quantified and understood by a combination of ML interatomic potentials, ML clustering techniques, and density functional theory calculations. This methodology allows us to process large amounts of atomic data to classify carbon atomic motifs on the basis of their geometry and quantify their reactivity toward hydrogen- and oxygen-containing functionalities. For instance, we identify subdivisions of sp and sp2 motifs with markedly different reactivities. We therefore draw a comprehensive, both qualitative and quantitative, picture of the surface chemistry of a-C and its reactivity toward −H, −O, −OH, and −COOH. While this paper focuses on a-C surfaces, the presented methodology opens up a new systematic and general way to study the surface chemistry of amorphous and disordered materials.

The influence of submarine groundwater discharge on nearshore marine dissolved organic carbon reactivity, concentration dynamics, and offshore export

Dissolved organic carbon (DOC) is the largest pool of reduced carbon in the oceans, with a reservoir equivalent to atmospheric CO2. In nearshore marine regions, DOC sources include primary production, terrestrial DOC delivered by river discharge, and/or terrestrial and marine DOC delivered via submarine groundwater discharge (SGD). While the importance of SGD to coastal carbon cycling has been implicated, the actual influence of this process on nearshore carbon dynamics and offshore export has not been explicitly identified. This study, conducted at a predominantly marine-influenced intertidal beach-nearshore ocean system along the Santa Barbara, California coastline, aimed to address this knowledge gap. Dark, temperature-controlled laboratory incubations, radioisotopic (radon-222) SGD estimates, and an SGD-DOC mixing-reaction box model were coupled to identify the influence of pore water mixing with seawater on nearshore DOC reactivity, concentration dynamics, and offshore export. Even with a relatively low volumetric contribution, SGD pore water mixing altered nearshore DOC reactivity, and elevated the nearshore DOC concentration by 0.4–6.6 µmol L−1 over nearshore seawater residence times spanning 1–6 days. These elevated DOC concentrations were equivalent to 0.5% to 9% of the mean offshore DOC concentration for the summer months in the Santa Barbara Channel, when the coastal water column is highly thermally stratified. Despite the challenge of assessing carbon dynamics in physically and biogeochemically complex nearshore marine regions, this study demonstrates the need for future investigations to assess and account for SGD as a non-trivial component of coastal marine carbon cycles.

On the reactivity of carbon formed from CO CVD over Ni(1 1 1)/TiO2

The formation and reactivity of carbon on the supported nickel catalyst is a key issue for the low temperature activity and stability with methanation, reforming and other reactions. In this work, Ni(1 1 1)/TiO2 was prepared and applied as the catalyst to deposit carbon using low temperature chemical vapor deposition (CVD) of carbon monoxide. It was found that the CVD temperature could significantly affect the formation of carbon. With the CVD temperature decreasing, the disorder of the carbon increased, while the degree of graphitization was reduced. As a result, graphene-like films can be obtained at low CVD temperatures (from 300 to 350 °C). Such carbon films show a significantly improved reactivity with hydrogen and carbon dioxide. This explains the excellent low temperature activity and stability for CO2 or CO methanation over Ni catalysts with Ni(1 1 1).

Singlet Oxygen Reactivity with Standard Li-Ion Battery Electrolyte Carbonate Solvents

Currently employed consumer batteries for high energy density applications rely on layered transition metal oxides as cathode active materials due to their high theoretical capacity and excellent capacity retention over prolonged cycling. Today’s research focus lies on Ni- and Li-rich materials (LiwNixCoyMnzO2 materials like NCM811 with w=1, x=0.8, y=z=0.1 or Li-rich high energy NCM (HE-NCM) with w+x+y+z=2 and w>1), motivated by a drive towards lower battery cost in $/kWh (1). However, today’s battery systems can only utilize roughly 70% of the maximum state of charge (SOC) range of NCMs (i.e., Δw = 0.0-0.7), as severe capacity fading is observed for higher SOC values, i.e., for higher cut-off potentials (2). On the other hand, Li-rich HE-NCM materials require activation to 100% SOC in the first cycle, and capacity and voltage fading are a challenge with these materials. Interestingly, molecular O2 release initiating at roughly 80% SOC has been observed for all these materials, which is accompanied by electrolyte oxidation (evident from CO2 and CO evolution) (3). As these coupled reactions always occur at roughly 80% SOC (i.e., at different potentials), they do not seem to originate from an electrochemical oxidation mechanism, for which one would expect a clear potential dependency. It was therefore concluded that the oxygen released must be highly reactive, and singlet oxygen (excited state 1Δg, furtheron referred to as 1O2) was suggested (4). Recently, experimental evidence for the validity has been found (5). The question remains how 1O2 can react with the electrolyte and why battery life is reduced so drastically once 1O2 release occurs. To examine these questions, an experimental set-up was designed for the on-line detection of the reaction products of carbonate solvents/electrolytes with 1O2. Artefacts arising from electrochemical processes can thus be excluded, and even the effect of conducting salts can be examined independently. The measurement is based on the formation of 1O2 by photoexcitation of the Rose Bengal dye in presence of ground-state triplet oxygen (6). Gaseous decomposition products are analyzed by on-line mass spectrometry, and solution species after illumination can be analyzed post-mortem by standard analytical methods. It was found that the reactivity of different carbonate solvents with 1O2 can vary substantially. To gain a mechanistic understanding on the reactivity of carbonates with 1O2 and to gather further insight into potentially detrimental reaction products, ab initio calculations to characterize the energy profile as well as dynamic on-the-fly simulations to explore the configuration space were performed. The results of gassing analysis and ab initio predicted transitions states and reaction products for the standard electrolyte solvent ethylene carbonate (EC) are shown in Fig. 1a and b, respectively. The on-line gassing analysis shows a clear CO2 evolution during excitation of the Rose Bengal dye which is accompanied by O2 consumption, proving the reactivity of 1O2 with EC. The only gaseous decomposition product is CO2, which is also found as product in the calculations shown in Fig. 1b. Analysis of the solution after reaction with 1O2 proves the formation of H2O2, which confirms the theoretically predicted reaction mechanism (Fig. 1b). This study provides experimental tools as well as computational concepts to understand the chemical reaction of 1O2 formed at the cathode/electrolyte interface with the electrolyte solvent and allows quantitative comparison of a large variety of solvents, starting from cyclic EC over linear diethyl and dimethyl carbonate to F-substituted carbonates like mono- and difluoro EC (FEC and DiFEC). Further evaluation of the effect of conducting salt and 1O2 scavengers can therewith be undertaken to get fundamental insights, with important implications for high-energy Li-Ion batteries. References G. E. Blomgren, J. Electrochem. Soc., 164, A5019 (2016). I. Buchberger, S. Seidlmayer, A. Pokharel, M. Piana, J. Hattendorff, P. Kudejova, R. Gilles and H. A. Gasteiger, J. Electrochem. Soc., 162, A2737 (2015). B. Strehle, K. Kleiner, R. Jung, F. Chesneau, M. Mendez, H. A. Gasteiger and M. Piana, J. Electrochem. Soc., 164, A400 (2017). R. Jung, M. Metzger, F. Maglia, C. Stinner and H. A. Gasteiger, J. Electrochem. Soc., 164, A1361 (2017). J. Wandt, A. T. S. Freiberg, A. Ogrodnik and H. A. Gasteiger, submitted (2018). M. DeRosa, Coord. Chem. Rev., 233-234, 351 (2002). Acknowledgements We thank Dr. Alexander Ogrodnik and Sophie Solchenbach from TUM for fruitful discussions. Fig. 1 : Reaction of EC with 1O2 . a) On-line gassing analysis of decomposition products and oxygen consumption during excitation of the Rose Bengal dye to produce 1O2 (t = 0-1 h). b) Reaction mechanism suggesting a stoichiometry of O2 consumed to CO2 formed of 2:1, whereby initiation of carbonate decomposition is caused by elimination of H2O2. Figure 1

ERT monitoring of gas injection into water saturated sands: Modelling and inversion of cross-hole laboratory data

A set of laboratory experiments were performed in order to investigate the capacity of the electrical resistivity tomography method to detect and monitor the circulation of gaseous CO2 into geological media. The experiments consisted of injecting reactive (CO2) or inert (N2) gases into reactive (carbonate) or inert (silica) sands saturated with water. The laboratory setup was a metric-scale cylindrical tank instrumented with electrodes placed on vertical rods, hence simulating a borehole to borehole monitoring network. The results demonstrated that the ERT method can efficiently detect, locate and image gas circulation plumes. Two main behaviors were identified: either an increase of the medium resistivity due to the invasion of the porous space by an electrically insulating gas phase, or a resistivity decrease induced by dissolution processes that enhance ionic concentrations in the saturating water. The observed anomalies showed varying geometric shapes depending on which type of sand was used. A 3D cellular automaton model was built and managed to reproduce different gas plume circulation patterns and the electrical resistivity response associated. This modeling work confirmed the link existing between the shapes of the resistivity anomalies, the gas plume geometry and the particle size distribution of the sand. Through a numerical sensitivity analysis, several measuring protocols were tested and developed in order to improve the imaging capacity of the electrical resistivity method. Results demonstrated that the most efficient protocol was different depending on the shape of the gas plume, thus stressing the importance of having a priori knowledge on the geological, lithological and hydraulic characteristics of the subsurface, in order to correctly assess the most likely gas plume geometry and hence design the most adapted monitoring protocol.

High-performance and stable La0.8Sr0.2Fe0.9Nb0.1O3-δanode for direct carbon solid oxide fuel cells fueled by activated carbon and corn straw derived carbon

The novel perovskite La0.8Sr0.2Fe0.9Nb0.1O3-δ (LSFNb) anode for direct carbon-solid oxide fuel cells (DC-SOFCs) is evaluated using activated carbon and corn straw carbon as fuels. Activated carbon possesses less ratio of disorder carbon, smaller average particle size and much higher specific surface area, as well as porous structure with micropores and mesopores compared with corn straw carbon. Electrolyte-supported DC-SOFCs with LSFNb anode demonstrate excellent performance with peak power densities of 302.8 mW cm−2 and 218.5 mW cm−2, respectively, when operated with activated carbon and corn straw carbon at 850 °C. Polarization resistances of LSFNb anode indicate that performance of DC-SOFCs is largely determined by the reverse Boudouard reaction, which is related to specific surface area of fuels. Cells fueled by corn straw carbon exhibit more stable output, higher released electric quantity and higher fuel utilization rate than that using activated carbon. Despite more disorder carbon and better thermal reactivity of corn straw carbon, higher initial output performance is obtained with activated carbon, proving that specific surface area of fuels, particle size and porosity have a considerable influence on the reverse Boudouard reaction and cell performance. These results indicate that LSFNb is a promising perovskite anode material for DC-SOFC.

Palladium‐Titanium Relay Catalysis Enables Switch from Alkoxide‐π‐Allyl to Dienolate Reactivity for Spiro‐Heterocycle Synthesis

AbstractReported herein is the divergent syntheses of [5,5] and [6,5] spiro‐heterocycles under Lewis‐acid‐assisted palladium catalysis. In particular, an unprecedented switch from alkoxide‐π‐allyl to dienolate reactivity was achieved by the use of palladium‐titanium relay catalysis, and represents umpolung reactivity of vinylethylene carbonates. This method uses a simple procedure and commercially available catalysts, and delivers both classes of spiro‐heterocycles, bearing three contiguous stereocenters, in high yield and uniformly excellent diastereoselectivity.

Palladium-Titanium Relay Catalysis Enables Switch from Alkoxide-π-Allyl to Dienolate Reactivity for Spiro-Heterocycle Synthesis.

Reported herein is the divergent syntheses of [5,5] and [6,5] spiro-heterocycles under Lewis-acid-assisted palladium catalysis. In particular, an unprecedented switch from alkoxide-π-allyl to dienolate reactivity was achieved by the use of palladium-titanium relay catalysis, and represents umpolung reactivity of vinylethylene carbonates. This method uses a simple procedure and commercially available catalysts, and delivers both classes of spiro-heterocycles, bearing three contiguous stereocenters, in high yield and uniformly excellent diastereoselectivity.