Anodic Cyclizations, Densely Functionalized Synthetic Building Blocks, and the Importance of Recent Mechanistic Observations

Anodic cyclization reactions can provide a versatile method for converting newly obtained chiral lactols to densely functionalized cyclic building blocks. The method works by first converting the lactol into an electron-rich olefin and then oxidatively generating a radical cation that is trapped by a nucleophile. Historically, such reactions have benefited from the use of less polar radical cations when the trapping nucleophile is a heteroatom and more polar radical cations when the reaction forms C-C bonds. This forced one to optimize underperforming reactions by resynthesizing the substrate. Here, we show that by taking advantage of methods that serve to drive a reversible initial cyclization reaction toward the product, this dichotomy and need to manipulate the substrate can be avoided. Two such methods were utilized: a faster second oxidation step and a mediated electrolysis. Both led to successful cyclizations using a polar radical cation and heteroatom nucleophiles.

Microelectrode Arrays, Electrocatalysis, and the Need for Proper Characterization

Indirect electrochemical methods are a powerful tool for synthetic chemistry because they allow for the optimization of chemical selectivity in a reaction while maintaining the advantages of electrochemistry in terms of sustainability. Recently, we have found that such methods provide a handle for not only the synthesis of complex molecules, but also the construction of complex, addressable molecular surfaces. In this effort, the indirect electrochemical methods enable the placement or synthesis of molecules by any electrode or set of electrodes in a microelectrode array. The success of these surface-based reactions are typically evaluated with the use of fluorescence labelling studies. However, these fluorescence-based evaluations can be misleading. While they are excellent for determining that a reaction has occurred in a site-selective fashion on an array, they do not provide information on whether that reaction is the one desired or how well it worked. We describe here how the use of a "safety-catch" linker strategy allows for a more accurate assessment of reaction quality on an array, and then use that capability to illustrate how the use of transition metal mediated cross-coupling reactions on an array prevent unwanted background reactions that can occur on a polymer-coated electrode surface. The method enables a unique level of quality control for array-based transformations.

Concluding remarks: A summary of the Faraday Discussion on electrosynthesis

A summary of the Faraday Discussion presented in this issue and a perspective on that discussion is presented. The work highlights the specific science contributions made and the key conclusions associated with those findings so that readers can identify papers that they would like to explore in more detail.

Anodic Cyclizations and Umpolung Reactions Involving Imines

Recent discoveries that anodic cyclization reactions rely heavily on the success of a second electron oxidation downstream of the cyclization suggest that this second electron oxidation step can be used to channel a reaction down new synthetic pathways. Here we describe one such application that reverses the normal reactivity of an imine group and sets the stage for the asymmetric synthesis of cyclic amines by anodic cyclization.

A Building Block Approach for the Total Synthesis of YM-385781

YM-254890 and FR900359 are potent and selective inhibitors of the Gq/11-signaling pathway. As such, they have been attractive targets for both synthesis and biological studies. Yet in spite of this effort, a versatile synthetic approach to the molecules that allows for the rapid construction of a variety of non-natural and labelled analogs and an increase in the amount of those analogs available remains elusive. We report here a convergent building block approach to the molecules that can solve this challenge.

Building Chemical Probes Based on the Natural Products YM-254890 and FR900359: Advances toward Scalability

The biological activity of natural products YM-254890 (YM) and FR900359 (FR) has led to significant interest in both their synthesis and the construction of more simplified analogs. While the simplified analogs lose much of the potency of the natural products, they are of interest in their own right, and their synthesis has revealed synthetic barriers to the family of molecules that need to be addressed if a scalable synthesis of YM and FR analogs is to be constructed. In the work described here, a synthetic route to simplified analogs of YM is examined and strategies for circumventing some of the challenges inherent to constructing the molecules are forwarded.

Microelectrode arrays, electrosynthesis, and the optimization of signaling on an inert, stable surface

Microelectrode arrays are powerful tools for monitoring binding interactions between small molecules and biological targets. In most cases, molecules to be studied using such devices are attached directly to the electrodes in the array. Strategies are in place for calibrating signaling studies utilizing the modified electrodes so that they can be quantified relative to a positive control. In this way, the relative binding constants for multiple ligands for a receptor can potentially be determined in the same experiment. However, there are applications of microelectrode arrays that require stable, tunable, and chemically inert surfaces on the electrodes. The use of those surfaces dictate the use of indirect detection methods that are dependent on the nature of the stable surface used and the amount of the binding partner that is placed on the surface. If one wants to do a quantitative study of binding events that involve molecules on such a stable surface, then once again a method for calibrating the signal from a positive control is needed. Fortunately, the electrodes in an array are excellent handles for conducting synthetic reactions on the surface of an array, and those reactions can be used to tune the surface above the electrodes and calibrate the signal from a positive control. Here, we describe how available Cu-based electrosynthetic reactions can be used to calibrate electrochemical signals on a polymer-coated electrode array and delineate the factors to be considered when choosing a polymer surface for such a study.

Lessons from an Array: Using an Electrode Surface to Control the Selectivity of a Solution-Phase Chemical Reaction

Electrochemistry offers a variety of novel means by which selectivity can be introduced into synthetic organic transformations. In the work reported, it is shown how methods used to confine chemical reactions to specific sites on a microelectrode array can also be used to confine a preparative reaction to the surface of an electrode inserted into a bulk reaction solution. In so doing, the surface of a modified electrode can be used to introduce new selectivity into a preparative reaction that is not observed in the absence of either the modified electrode surface or the effort to confine the reaction to that surface. The observed selectivity can be optimized in the same way that confinement is optimized on an array and is dependent on the nature of the functionalized surface.

Capitalizing on Mediated Electrolyses for the Construction of Complex, Addressable Molecular Surfaces

Synthetic organic chemists are beginning to exploit electrochemical methods in increasingly creative ways. This is leading to a surge in productivity that is only now starting to take advantage of the full-potential of electrochemistry for accessing new structures in novel, more efficient ways. In this perspective, we provide insight into the potential of electrochemistry as a synthetic tool gained through studies of both direct anodic oxidation reactions and more recent indirect methods, and highlight how the development of new electrochemical methods can expand the nature of synthetic problems our community can tackle.

Microelectrode Arrays, Dihydroxylation, and the Development of an Orthogonal Safety-Catch Linker

Construction of larger molecular libraries on an addressable microelectrode array requires a method for recovering and characterizing molecules from the surface of any electrode in the array. This method must be orthogonal to the synthetic strategies needed to build the array. We report here a method for achieving this goal that employs the site-selective dihydroxylation reaction of a simple olefin.

Anodic Olefin Coupling Reactions: Elucidating Radical Cation Mechanisms and the Interplay between Cyclization and Second Oxidation Steps

Anodic olefin coupling reactions generate new bonds and ring skeletons through a net two electron process that reverses the polarity of a known, electron-rich functional group. While much of the early work on the mechanism of these reactions focused on the initial oxidation and cyclization steps of the process, the second oxidation step also plays a central role in determining the success of the reaction. Evidence supporting this observation is presented, along with evidence that optimization of this second oxidation step is not enough to pull a poor cyclization to the desired product. Successful cyclization reactions require optimization of both processes.

Organic Electrochemistry: Expanding the Scope of Paired Reactions

Paired electrochemical reactions allow the optimization of both atom and energy economy of oxidation and reduction reactions. While many paired electrochemical reactions take advantage of perfectly matched reactions at the anode and cathode, this matching of substrates is not necessary. In constant current electrolysis, the potential at both electrodes adjusts to the substrates in solution. In principle, any oxidation reaction can be paired with any reduction reaction. Various oxidation reactions conducted on the anodic side of the electrolysis were paired with the generation and use of hydrogen gas at the cathode, showing the generality of the anodic process in a paired electrolysis and how the auxiliary reaction required for the oxidation could be used to generate a substrate for a non-electrolysis reaction. This is combined with variations on the cathodic side of the electrolysis to complete the picture and illustrate how oxidation and reduction reactions can be combined.

From Molecules to Molecular Surfaces. Exploiting the Interplay Between Organic Synthesis and Electrochemistry

For many years, we have been looking at electrochemistry as a tool for exploring, developing, and implementing new synthetic methods for the construction of organic molecules. Those efforts examined electrochemical methods and mechanisms and then exploited them for synthetic gain. Chief among the tools utilized was the fact that in a constant current electrolysis the working potential at the electrodes automatically adjusted to the oxidation (anode) or reduction (cathode) potential of the substrates in solution. This allowed for a systematic examination of the radical cation intermediates that are involved in a host of oxidative cyclization reactions. The result has been a series of structure-activity studies that have led to far greater insight into the behavior of radical cation intermediates and in turn an expansion in our capabilities of using those intermediates to trigger interesting synthetic reactions. With that said, the relationship between synthetic organic chemistry and electrochemistry is not a "one-way" interaction. For example, we have been using modern synthetic methodology to construct complex addressable molecular surfaces on electroanalytical devices that in turn can be used to probe biological interactions between small molecules and biological receptors in "real-time". Synthetic chemistry can then be used to recover the molecules that give rise to positive signals so that they can be characterized. The result is an analytical method that both gives accurate data on the interactions and provides a unique level of quality control with respect to the molecules giving rise to that data. Synthetic organic chemistry is essential to this task because it is our ability to synthesize the surfaces that defines the nature of the biological problems that can be studied. But the relationship between the fields does not end there. Recently, we have begun to show that work to expand the scope of microelectrode arrays as bioanalytical devices is teaching us important lessons for preparative synthetic chemistry. These lessons come in two forms. First, the arrays have taught us about the on-site generation of chemical reagents, a lesson that is being used to expand the use of paired electrochemical strategies for synthesis. Second, the arrays have taught us that reagents can be generated and then confined to the surface of the electrode used for that generation. This has led to a new approach to taking advantage of molecular recognition events that occur on the surface of an electrode for controlling the selectivity of a preparative reaction. In short, the confinement strategy developed for the arrays is used to ensure that the chemistry in a preparative electrolysis happens at the electrode surface and not in the bulk solution. This Account details the interplay between synthetic chemistry and electrochemistry in our group through the years and highlights the opportunities that interplay has provided and will continue to provide in the future.

Anti-hypertensive mechanisms of cyclic depsipeptide inhibitor ligands for Gq/11 class G proteins

Augmented vasoconstriction is a hallmark of hypertension and is mediated partly by hyper-stimulation of G protein couple receptors (GPCRs) and downstream signaling components. Although GPCR blockade is a key component of current anti-hypertensive strategies, whether hypertension is better managed by directly targeting G proteins has not been thoroughly investigated. Here, we tested whether inhibiting G_q/11 proteins in vivo and ex vivo using natural cyclic depsipeptide, FR900359 (FR) from the ornamental plant, Ardisia crenata, and YM-254890 (YM) from Chromobacterium sp. QS3666, or it's synthetic analog, WU-07047 (WU), was sufficient to reverse hypertension in mice. All three inhibitors blocked G protein-dependent vasoconstriction, but to our surprise YM and WU and not FR inhibited K⁺-induced Ca²⁺ transients and vasoconstriction of intact vessels. However, each inhibitor blocked whole-cell L-type Ca²⁺ channel current in vascular smooth muscle cells. Subcutaneous injection of FR or YM (0.3 mg/kg, s.c.) in normotensive and hypertensive mice elicited bradycardia and marked blood pressure decrease, which was more severe and long lasting after the injection of FR relative to YM (FR_t1/2 ≅ 12 h vs. YM_t1/2 ≅ 4 h). In deoxycorticosterone acetate (DOCA)-salt hypertension mice, chronic injection of FR (0.3 mg/kg, s.c., daily for seven days) reversed hypertension (vehicle SBP: 149 ± 5 vs. FR SBP: 117 ± 7 mmHg), without any effect on heart rate. Our results together support the hypothesis that increased LTCC and G_q/11 activity is involved in the pathogenesis of hypertension, and that dual targeting of both proteins can reverse hypertension and associated cardiovascular disorders.

Organic Electrochemistry and a Role Reversal: Using Synthesis To Optimize Electrochemical Methods

Diblock copolymers are excellent coatings for microelectrode arrays because they provide a stable surface that can support both synthetic and analytical electrochemistry. However, the surfaces that are optimal for synthetic studies are not the same as the surfaces that are optimal for analytical studies. Hence, no one surface provides an ideal platform for both building and analyzing a molecular library. Fortunately, the synthetic chemistry available on a microelectrode array allows a surface that is ideal for synthesis can be converted into one that is ideal for signaling studies; a scenario that allows for the use of an optimized synthetic and analytical surface on a single microelectrode array.

Anodic Cyclization Reactions and the Mechanistic Strategies That Enable Optimization

Oxidation reactions are powerful tools for synthesis because they allow us to reverse the polarity of electron-rich functional groups, generate highly reactive intermediates, and increase the functionality of molecules. For this reason, oxidation reactions have been and continue to be the subject of intense study. Central to these efforts is the development of mechanism-based strategies that allow us to think about the reactive intermediates that are frequently central to the success of the reactions and the mechanistic pathways that those intermediates trigger. For example, consider oxidative cyclization reactions that are triggered by the removal of an electron from an electron-rich olefin and lead to cyclic products that are functionalized for further elaboration. For these reactions to be successful, the radical cation intermediate must first be generated using conditions that limit its polymerization and then channeled down a productive desired pathway. Following the cyclization, a second oxidation step is necessary for product formation, after which the resulting cation must be quenched in a controlled fashion to avoid undesired elimination reactions. Problems can arise at any one or all of these steps, a fact that frequently complicates reaction optimization and can discourage the development of new transformations. Fortunately, anodic electrochemistry offers an outstanding opportunity to systematically probe the mechanism of oxidative cyclization reactions. The use of electrochemical methods allows for the generation of radical cations under neutral conditions in an environment that helps prevent polymerization of the intermediate. Once the intermediates have been generated, a series of "telltale indicators" can be used to diagnose which step in an oxidative cyclization is problematic for less successful transformation. A set of potential solutions to address each type of problem encountered has been developed. For example, problems with the initial cyclization reaction leading to either polymerization of the radical cation, elimination of a proton from or solvent trapping of that intermediate, or solvent trapping of the radical cation can be identified in the proton NMR spectrum of the crude reaction material. Such an NMR spectrum shows retention of the trapping group. The problems can be addressed by tuning the radical cation, altering the trapping group, or channeling the reactive intermediate down a radical pathway. Specific examples each are shown in this Account. Problems with the second oxidation step can be identified by poor current efficiency or general decomposition in spite of cyclic voltammetry evidence for a rapid cyclization. Solutions involve improving the oxidation conditions for the radical after cyclization by either the addition of a properly placed electron-donating group in the substrate or an increase in the concentration of electrolyte in the reaction (a change that stabilizes the cation generated from the second oxidation step). Problems with the final cation typically lead to overoxidation. Solutions to this problem require an approach that either slows down elimination side reactions or changes the reaction conditions so that the cation can be quickly trapped in an irreversible fashion. Again, this Account highlights these strategies along with the specific experimental protocols utilized.

Abstract P103: Anti-hypertensive Mechanisms of Action of G q/11 Inhibitor Ligands

Chronic blockade of individual G protein coupled receptors (GPCRs) has proven to be inadequate strategy for managing hypertension partly because the subcellular heterotrimeric G proteins that propagate intracellular signaling can simultaneously couple to several other vasopressor receptors. Whether blood pressure can better be controlled by directly targeting G proteins has not been thoroughly investigated due to paucity of selective, cell-permeable inhibitors. Here, we tested whether chemical inhibition of Gq/11 proteins in vivo and ex vivo using recently discovered small-molecule inhibitor ligands, YM-254890 (YM), FR-900359 (FR) and WU-07047 (WU) is sufficient to reverse hypertension in mice. Using ex vivo vessel reactivity assay, we found that Gq/11 inhibitors markedly reduced vasoconstriction evoked with phenylephrine (PE), vasopressin, endothelin-1, and the thromboxane analog U-46619. Blockade of PE-induced contractility by the Gq/11 inhibitors showed the following rank-order potency: FR LogIC50 -0.008 ± 0 > YM LogIC50 -0.49 ± 0 > WU LogIC50 -64.95 ± 6.4. YM and WU but not FR inhibited PE-induced vasoconstriction through G protein-dependent and independent pathways by blocking L-type calcium channel-mediated Ca 2+ influx. Acute subcutaneous injection of FR and YM (0.3 mg/kg, s.c.) in normotensive and N ω -Nitro-L-arginine methyl ester (L-NAME) hypertension mice elicited marked hypotension, which was more severe (ΔSBP = -25 ± 2.7 vs. ΔSBP = -21 ± 2.2 mmHg) and long lasting (FR t1/2 ≅ 12 hr vs. YM t1/2 ≅ 4 hr) after the injection of FR relative to YM. In DOCA-salt hypertension mice, chronic injection of FR (0.3 mg/kg, s.c., daily for seven days) reversed hypertension (vehicle SBP: 149 ± 5 vs. FR SBP: 117 ± 7 mmHg) and sustained blood pressure reduction several days after terminating the injection regimen (DOCA SBP: 141 ± 2 vs. SBP 5 days post FR: 128 ± 5 mmHg). Our results together support the hypothesis that increased Gq/11 activity in blood pressure-regulating organs is involved in the pathogenesis of hypertension, and that direct systemic blockade of Gq/11 reverses hypertension. The findings provide clear evidence for targeting Gq/11 in the cardiovascular system as an effective therapy for treating hypertension.

Insights into the Mechanism of Anodic N-N Bond Formation by Dehydrogenative Coupling

The electrochemical synthesis of pyrazolidine-3,5-diones and benzoxazoles by N-N bond formation and C,O linkage, respectively, represents an easy access to medicinally relevant structures. Electrochemistry as a key technology ensures a safe and sustainable approach. We gained insights in the mechanism of these reactions by combining cyclovoltammetric and synthetic studies. The electron-transfer behavior of anilides and dianilides was studied and led to the following conclusion: The N-N bond formation involves a diradical as intermediate, whereas the benzoxazole formation is based on a cationic mechanism. Besides these studies, we developed a synthetic route to mixed dianilides as starting materials for the N-N coupling. The compatibility with valuable functionalities like triflates and mesylates for follow-up reactions as well as the comparison of different electrochemical set-ups also enhanced the applicability of this method.

Electrochemical synthesis of benzoxazoles from anilides – a new approach to employ amidyl radical intermediates

The electroorganic synthesis of a variety of benzoxazoles starting from easy accessible anilides is reported.

New Methods for the Site-Selective Placement of Peptides on a Microelectrode Array: Probing VEGF-v107 Binding as Proof of Concept

Cu(I)-catalyzed "click" reactions cannot be performed on a borate ester derived polymer coating on a microelectrode array because the Cu(II) precursor for the catalyst triggers background reactions between both acetylene and azide groups with the polymer surface. Fortunately, the Cu(II)-background reaction can itself be used to site-selectively add the acetylene and azide nucleophiles to the surface of the array. In this way, molecules previously functionalized for use in "click" reactions can be added directly to the array. In a similar fashion, activated esters can be added site-selectively to a borate ester coated array. The new chemistry can be used to explore new biological interactions on the arrays. Specifically, the binding of a v107 derived peptide with both human and murine VEGF was probed using a functionalized microelectrode array.

RGS2 squelches vascular Gi/o and Gq signaling to modulate myogenic tone and promote uterine blood flow

Uterine artery blood flow (UABF) is critical to maintaining uterine perfusion in nonpregnant states and for uteroplacental delivery of nutrients and oxygen to the fetus during pregnancy. Impaired UABF is implicated in infertility and several pregnancy complications including fetal growth restriction, small for gestational age, and preeclampsia. The etiology of abnormal UABF is not known. Here, we determined whether deficiency or loss of RGS2, a GTPase-activating protein for Gq/11 and Gi/o class G proteins, affects UABF in nonpregnant mice. We used Doppler ultrasonography to assess UABF in wild type (WT), Rgs2 heterozygous (Rgs2+/-), and homozygous knockout (Rgs2-/-) mice. Video microscopy was used for ex vivo examination of uterine artery myogenic tone and fura-2 imaging for in vitro assessment of internal stores Ca(2+) release. We found that baseline UABF velocity was markedly decreased while impedance measured as resistive index (WT = 0.58 ± 0.04 vs. Rgs2-/- = 0.71 ± 0.03, P < 0.01) and pulsatile index (WT = 0.90 ± 0.06 vs. Rgs2-/- = 1.25 ± 0.11, P < 0.01) was increased in Rgs2-/- mice. Uterine artery tone was augmented in Rgs2+/- and Rgs2-/- mice, which was normalized to WT levels following Gi/o and Gq inactivation. Conversely, blockade of ryanodine receptors increased WT myogenic tone to RGS2 mutant levels. The data together indicate that RGS2 deficiency decreases UABF by increasing myogenic tone at least partly through prolonged G protein activation. Mutations that decrease vascular RGS2 expression may be a predisposition to decreased uterine blood flow. Targeting G protein signaling therefore might improve uterine and uteroplacental underperfusion disorders.

Considering organic mechanisms and the optimization of current flow in an electrochemical oxidative condensation reaction

Careful consideration of the chemical mechanism for an oxidative condensation reaction led to improved current flow for the electrolysis.

Solvolysis, Electrochemistry, and Development of Synthetic Building Blocks from Sawdust

Either aldehyde or cinnamyl ether products can be selectively extracted from raw sawdust by controlling the temperature and pressure of a solvolysis reaction. These materials have been used as platform chemicals for the synthesis of 15 different synthetic substrates. The conversion of the initial sawdust-derived materials into electron-rich aryl substrates often requires the use of oxidation and reduction chemistry, and the role electrochemistry can play as a sustainable method for these transformations has been defined.

Practical Electrochemical Anodic Oxidation of Polycyclic Lactams for Late Stage Functionalization

Electrochemistry provides a powerful tool for the late-stage functionalization of complex lactams. A two-stage protocol for converting lactams, many of which can be prepared through the intramolecular Schmidt reaction of keto azides, is presented. In the first step, anodic oxidation in MeOH using a repurposed power source provides a convenient route to lactams bearing a methoxy group adjacent to nitrogen. Treatment of these intermediates with a Lewis acid in dichloromethane permits the regeneration of a reactive acyliminium ion that is then reacted with a range of nucleophilic species.

Introduction to Microelectrode Arrays, the Site-Selective Functionalization of Electrode Surfaces, and the Real-Time Detection of Binding Events

Microelectrode arrays have great potential as analytical tools because currents can be independently measured at each electrode in the array. In principle, these currents can be monitored in order to follow in real time the binding events that occur between the members of a molecular library and a biological target. To capitalize on this potential, the surface of the array must be selectively functionalized so that each unique member of the molecular library is associated with a unique individually addressable electrode or set of electrodes in the array. To this end, this instructional review summarizes methods for coating the arrays with porous polymers that allow for the attachment of molecules to the surface of the array, selectively conducting reactions at individual electrodes in the array, characterizing molecules that are placed on the arrays, and running the analytical experiments needed to monitor in real time binding events between molecules on the array and a biological target.

Photovoltaic-driven organic electrosynthesis and efforts toward more sustainable oxidation reactions

The combination of visible light, photovoltaics, and electrochemistry provides a convenient, inexpensive platform for conducting a wide variety of sustainable oxidation reactions. The approach presented in this article is compatible with both direct and indirect oxidation reactions, avoids the need for a stoichiometric oxidant, and leads to hydrogen gas as the only byproduct from the corresponding reduction reaction.

Microelectrode Arrays and the Use of PEG-Functionalized Diblock Copolymer Coatings

PEG-modified diblock copolymer surfaces have been examined for their compatibility with microelectrode array based analytical methods. The use of PEG-modified polymer surfaces on the arrays was initially problematic because the redox couples used in the experiments were adsorbed by the polymer. This led the current measured by cyclic voltammetry for the redox couple to be unstable and increase with time. However, two key findings allow the experiments to be successful. First, after multiple cyclic voltammograms the current associated with the redox couple does stabilize so that a good baseline current can be established. Second, the rate at which the current stabilizes is consistent every time a particular coated array is used. Hence, multiple analytical experiments can be conducted on an array coated with a PEG-modified diblock copolymer and the data obtained is comparable as long as the data for each experiment is collected at a consistent time point.

Microelectrode arrays: a general strategy for using oxidation reactions to site selectively modify electrode surfaces

Oxidation reactions are powerful tools for synthesis because they allow for the functionalization of molecules. Here, we present a general method for conducting these reactions on a microelectrode array in a site-selective fashion. The reactions are run as a competition between generation of a chemical oxidant at the electrodes in the array and reduction of the oxidant by a "confining agent" in the solution above the array. The "confining agent" does not need to be more reactive than the substrate fixed to the surface of the array. In many cases, the same substrate placed on the surface of the array can also be used in solution as the confining agent.

Oxidative cyclization reactions: controlling the course of a radical cation-derived reaction with the use of a second nucleophile

Construction of new ring systems: Oxidative cyclizations (see picture; RVC=reticulated vitreous carbon) have been conducted that use two separate intramolecular nucleophiles to trap an enol ether-derived radical cation intermediate. The reactions provide a means for rapidly trapping the radical cation intermediate in a manner that avoids competitive decomposition reactions.

Anodic coupling of carboxylic acids to electron-rich double bonds: A surprising non-Kolbe pathway to lactones

Carboxylic acids have been electro-oxidatively coupled to electron-rich olefins to form lactones. Kolbe decarboxylation does not appear to be a significant competing pathway. Experimental results indicate that oxidation occurs at the olefin and that the reaction proceeds through a radical cation intermediate.