Exploiting Visible Light Triggered Formation of trans-Cyclohexene for the Contra-thermodynamic Protection of Alcohols

We report herein a method for the contra-thermodynamic protection and thermodynamic deprotection of alcohols in which all reagents are returned to their original state. This is accomplished by the use of visible light photochemical energy to drive the formation of a highly strained trans-(Z)-cyclohexene. At STP the product ethers contain more potential energy than the starting materials and, thus, can be catalytically returned to the starting materials, effectively realizing a protection-deprotection scheme paid for with an energy currency.

Efforts toward Synthetic Photosynthesis: Visible Light-Driven CO2 Valorization

Current methods of urethane preparation from amines invariably involve high-energy and often toxic or cumbersome molecules to make the process exergonic. CO2 aminoalkylation using olefins and amines represents an attractive albeit endergonic alternative. We report a moisture-tolerant method that uses visible light energy to drive this endergonic process (+25 kcal/mol at STP) using sensitized arylcyclohexenes. They convert much of the photon's energy to strain upon olefin isomerization. This strain energy greatly enhances alkene basicity, allowing for sequential protonation by and interception of ammonium carbamates. Following optimization steps and amine scope evaluation, an example product arylcyclohexyl urethane underwent transcarbamoylation with some demonstrative alcohols to form more general urethanes with concomitant regeneration of the arylcyclohexene. This represents a closure of the energetic cycle, producing H2O as the stoichiometric byproduct.

Development of novel fluor mop materials for remediation of perfluoroalkyl substances (PFAS) from groundwater

In this study we synthesized a library of 12 novel adsorbent materials that utilize a chemically well-defined silica support for superior removal of PFAS from real groundwater from a contaminated United States Air Force base. The library of sorbents probed the importance of a fluorous, hydrophobic, and electrostatic components in the removal efficacy. The materials were assessed in batch studies with PFOA, PFOS, and PFBA and compared directly to GAC and Ion Exchange resin. Adsorption kinetics with PFOS were best fit to a pseudo-second order model and equilibrium data fit well to a Langmuir isotherm model. The results were also validated externally, and the best performing material removed greater than 90% of 8 PFAS tested and was able to be regenerated up to 5 cycles. The results provide a top performing material that with further testing can be used to clean up environmentally contaminated water and provide support for the theory that a fluorous component when combined with the electrostatic and hydrophobic components, imparts both enhanced PFAS selectivity and functional resilience to the material.

Molecular Sculpting: A Multipurpose Tool for Expedited Access to Various Fluorinated Arenes via Photocatalytic Hydrodefluorination of Benzoates

Starting with highly fluorinated benzoates, we develop the directed photocatalytic hydrodefluorination (HDF) of fluorinated aryl benzoates and demonstrate its synergistic use with other HDF strategies, along with C-H arylation, decarboxylative coupling, and decarboxylative protonation, to access most fluorination patterns found in benzoate derivatives and by extension benzene derivatives via a molecular sculpting approach. Mild reaction conditions and excellent regioselectivity make the approach ideal for synthesis. This approach provides access to 16 benzoate derivatives with different fluorination patterns from just a couple of highly fluorinated, commercially available benzoic acids. We synthesize key intermediates or the active pharmaceutical ingredient for sitagliptin, diflunisal, and other pharmaceutically important molecules. Importantly, we provide key insights into relative rates of defluorination and strategies to alter these rates. We provide demonstrations of the synergistic use of HDF and related technologies to rapidly enhance the synthetic complexity of these simple commercially available perfluoroarenes to form complex partially fluorinated molecules.

A new twist for Stork-Danheiser products enabled by visible light mediated trans-cyclohexene formation; access to acyclic distal enones

Herein, we investigate the use of visible light to indirectly drive ring opening in unstrained 6- and 7-membered ring systems via reaction with a transiently generated trans-cycloalkene. Identification of conditions that capture visible light energy in the form of ring strain was key to success. Under mildly acidic conditions, cycloalkenols were shown to undergo formally endothermic ring-opening isomerization to give acyclic exo-methylene and distal ketones or aldehydes in high yields. Ultimately, this work demonstrates the ability of cycloalkenes to capture visible light energy and its use to drive both kinetically and thermally unfavorable rearrangements.

A Selective Single Step Amidation of Polyfluoroarenes

This chemistry establishes a method for the synthesis of per- and poly-fluoroaryl acid amides, utilizing nucleophilic aromatic substitution. Traditionally, such amides are constructed in a two-step process, namely, ammonolysis and then N-acylation. Herein, good yields of N-polyfluoroaryl acid amides were achieved in a single step under mild reaction conditions. Key to achieving optimal yields is the use of two equivalents of the nucleophile. In addition, the mechanism of the reaction is discussed which has implications for other related nucleophilic substitutions.

Catalyst-Free Hydrodefluorination of Perfluoroarenes with NaBH4

Presented is an economical means of removing fluorine from various highly fluorinated arenes using NaBH₄. The procedure was adapted for different classes of perfluoroarenes. A novel isomer of an emerging class of organic dyes based on the carbazole phthalonitrile motif was succinctly synthesized in two steps from tetrafluorophthalonitrile, demonstrating the utility of the hydrodefluorination procedure. Initial exploration of the dye shows it to be photoactive and capable of facilitating contrathermodynamic styrenoid E/Z isomerization.

Coupling Photocatalysis and Substitution Chemistry to Expand and Normalize Redox-Active Halides

Photocatalysis can generate radicals in a controlled fashion and has become an important synthetic strategy. However, limitations due to the reducibility of alkyl halides prevent their broader implementation. Herein we explore the use of nucleophiles that can substitute the halide and serve as an electron capture motif that normalize the variable redox potentials across substrates. When used with photocatalysis, bench-stable, commercially available collidinium salts prove to be excellent radical precursors with a broad scope.

Solubility of Iridium and Ruthenium Organometallic Photoredox Catalysts

Despite the exponential growth of the field of photocatalysis, for reasons that are not entirely clear, these precious photocatalysts are often used in the literature at loadings that exceed their maximum solubility. On an industrial scale, the quantity of any precious metal catalyst can be a substantial financial burden or a sourcing issue, not to mention concerns as to the ecological and earth abundance of these catalysts. We believe that inattention to solubility has made these reactions appear less efficient than they actually are, because much of the photocatalyst remains undissolved. Therefore, the maximum solubilities of iridium and ruthenium centered photocatalysts have been systematically identified in industrially relevant solvents. Further, a literature photocatalytic reaction which our results suggested was beyond the maximum solubility has been revisited, with interesting results.

An elusive thermal [2 + 2] cycloaddition driven by visible light photocatalysis: tapping into strain to access C2-symmetric tricyclic rings

A mild and operationally simple methodology is reported for the synthesis of cyclobutane rings imbedded within a C2-symmetric tricyclic framework. The method uses visible light and an iridium-based photocatalyst to drive the oft-stated "forbidden" thermal [2 + 2] cycloaddition of cycloheptenes and analogs. Importantly, it generates cyclobutane with four new stereocenters with excellent stereoselectivity, and perfect regioselectivity. The reaction is propelled forward when the photocatalyst absorbs a visible light photon, which transfers this energy to the cycloheptene. Key to success is, upon excitation to the triplet via sensitization from the photocatalyst, the double bond isomerizes to give the transient, highly strained, trans-cycloheptene. The trans-cycloheptene undergoes a strain relieving thermal, intermolecular [π2s + π2a] cycloaddition with another cis-cycloheptene. X-ray analysis reveals that the major product is the head-to-head, C2-symmetric all trans-cyclobutane. Additionally, a dramatic display structural complexity enhancement is observed with the use of chiral cycloheptenols possessing one stereocenter, which results in the formation of cyclobutanes with six contiguous stereocenters with good to excellent diastereocontrol, and can be used to isolate single stereoisomers of stereochemically complex cyclobutanes in good yield.

Correction: An elusive thermal [2 + 2] cycloaddition driven by visible light photocatalysis: tapping into strain to access C2-symmetric tricyclic rings

Correction for 'An elusive thermal [2 + 2] cycloaddition driven by visible light photocatalysis: tapping into strain to access C2-symmetric tricyclic rings' by Kamaljeet Singh et al., Org. Biomol. Chem., 2018, DOI: 10.1039/c8ob01273c.

Prenyl Praxis: A Method for Direct Photocatalytic Defluoroprenylation

The prenyl fragment is the quintessential constituent of terpenoid natural products, a diverse family which contains numerous members with diverse biological properties. In contrast, fluorinated and multifluorinated arenes make up an important class of anthropogenic molecules which are highly relevant to material, agricultural, and pharmaceutical industries. While allylation chemistry is well developed, effective prenylation strategies have been less forthcoming. Herein, we describe the photocatalytic defluoroprenylation, a powerful method that provides access to "hybrid molecules" that possess both the functionality of a prenyl group and fluorinated arenes. This approach involves direct prenyl group transfer under very mild conditions, displays excellent functional group tolerance, and includes relatively short reaction times (<4 h), which is the fastest photocatalytic C-F functionalization developed to date. Additionally, the strategy can be extended to include allyl and geranyl (10 carbon fragment) transfers. Another prominent finding is a reagent-dependent switch in regioselectivity of the major product from para to ortho C-F functionalization.

Formation of Non-Natural α,α-Disubstituted Amino Esters via Catalytic Michael Addition

The enolate monoanion of amino esters is explored, and the first catalytic Michael addition of α-amino esters is demonstrated. These studies indicate that the acidity of the αC-H is the primary factor determining reactivity. Thus, polyfluorophenylglycine amino esters yield novel α-amino esters in the presence of a catalytic amount of a guanidine-derived base and Michael acceptors. Reactivity requires an acidic N-H, which is accomplished using common protecting groups such as N-Bz, N-Boc, and N-Cbz. Calculations and labeling experiments provide insight into the governing principles in which a key C-to-N proton transfer occurs, resulting in an expansion of the scope to include a number of natural amino esters. The study culminates with a late-stage functionalization of peptidic γ-secretase inhibitor, DAPT.

Characterizing fretting damage in different test media for cardiovascular device durability testing

In vitro durability tests of cardiovascular devices are often used to evaluate the potential for fretting damage during clinical use. Evaluation of fretting damage is important because severe fretting can concentrate stress and lead to the loss of structural integrity. Most international standards call for the use of phosphate buffered saline (PBS) for such tests although there has been little evidence to date that the use of PBS is appropriate in terms of predicting the amount of fretting damage that would occur in vivo. In order to determine an appropriate test media for in vitro durability tests where fretting damage is being evaluated, we utilized an in vitro test that is relevant to cardiovascular devices both in terms of dimensions and materials (nitinol, cobalt-chromium, and stainless steel) to characterize fretting damage in PBS, deionized water (DIW), and heparinized porcine blood. Overall, tests conducted in blood were found to have increased levels of fretting damage over tests in DIW or PBS, although the magnitude of this difference was smaller than the variability for each test media. Tests conducted in DIW and PBS led to mostly similar amounts of fretting damage with the exception of one material combination where DIW had greatly reduced damage compared to PBS and blood. Differences in fretting damage among materials were also observed with nitinol having less fretting damage than stainless steel or cobalt-chromium. In general, evaluating fretting damage in PBS or DIW may be appropriate although caution should be used when selecting test media and interpreting results given some of the differences observed across different materials.

Polyfluoroarylation of oxazolones: access to non-natural fluorinated amino acids

Herein, conditions are provided for the formation and use of the oxazolone enolate for the nucleophilic substitution of highly fluorinated (hetero)arenes, which after unmasking yield highly fluorinated non-natural amino acids and derivatives. In addition, the properties and chemical behavior of this new class of amino acids are explored. The utility is demonstrated in the one pot synthesis of medicinally relevant 2-aminohydantoins.

Prediction of 19F NMR Chemical Shifts for Fluorinated Aromatic Compounds

Scaling factors are reported for use in predicting ¹⁹F NMR chemical shifts for fluorinated (hetero)aromatic compounds with relatively low levels of theory. Our recommended scaling factors were developed using a curated data set of 52 compounds, with 100 individual ¹⁹F shifts spanning a range of 153 ppm. With a maximum deviation of 6.5 ppm between experimental and computed shifts, or 4% of the range tested, these scaling factors allow for the assignment of chemical shifts to specific fluorines in multifluorinated aromatics. The utility of this approach is highlighted by several structural reassignments.

Hydrogen Bond Directed Photocatalytic Hydrodefluorination: Overcoming Electronic Control

The photocatalytic C-F functionalization of highly fluorinated arenes is a powerful method for accessing functionalized multifluorinated arenes. The decisive step in the determining regioselectivity in fluorine functionalization is fluoride fragmentation from the radical anion of the multifluorinated arene. To date, the availability of regioisomers has been dictated by the innate electronics of the fluorinated arene, limiting the synthetic utility of the chemistry. This study investigates the remarkable ability of a strategically located hydrogen bond to transcend the normal regioselectivity of the C-F functionalization event. A significant rate acceleration is additionally observed for hydrodefluorination of fluorines that can undergo intramolecular hydrogen bonds that form 5-8-membered cycles with moderately acidic N-H's. The hydrogen bond is expected to facilitate the fragmentation not only by bending the C-F bond of the radical anion out of planarity but also by increasing the exothermicity of the fluoride extrusion step through protonation of the naked fluoride. Finally, the synthetic utility of the method is demonstrated in an expedited synthesis of the trifluorinated α-phenyl acetic acid derivative required for the commercial synthesis of Januvia, an antidiabetic drug. This represents the first synthesis of a commercially important multifluorinated arene via a defluorination strategy and is significantly shorter than the current strategy.

Sodium Hypochlorite Treatment and Nitinol Performance for Medical Devices

Processing of nitinol medical devices has evolved over the years as manufacturers have identified methods of reducing surface defects such as inclusions. One recent method proposes to soak nitinol medical devices in a 6% sodium hypochlorite (NaClO) solution as a means of identifying surface inclusions. Devices with surface inclusions could in theory then be removed from production because inclusions would interact with NaClO to form a visible black material on the nitinol surface. To understand the effects of an NaClO soak on performance, we compared as-received and NaClO-soaked nitinol wires with two different surface finishes (black oxide and electropolished). Pitting corrosion susceptibility was equivalent between the as-received and NaClO-soaked groups for both surface finishes. Nickel ion release increased in the NaClO-soaked group for black oxide nitinol, but was equivalent for electropolished nitinol. Fatigue testing revealed a lower fatigue life for NaClO-soaked black oxide nitinol at all alternating strains. With the exception of 0.83% alternating strain, NaClO-soaked and as-received electropolished nitinol had similar average fatigue life, but the NaClO-soaked group showed higher variability. NaClO-soaked electropolished nitinol had specimens with the lowest number of cycles to fracture for all alternating strains tested with the exception of the highest alternating strain 1.2%. The NaClO treatment identified only one specimen with surface inclusions and caused readily identifiable surface damage to the black oxide nitinol. Damage from the NaClO soak to electropolished nitinol surface also appears to have occurred and is likely the cause of the increased variability of the fatigue results. Overall, the NaClO soak appears to not lead to an improvement in nitinol performance and seems to be damaging to the nitinol surface in ways that may not be detectable with a simple visual inspection for black material on the nitinol surface.

Selective and Scalable Perfluoroarylation of Nitroalkanes

Functionalized per- and polyfluoroarenes are important building blocks, with many industrially and medicinally important molecules containing them. Nucleophilic aromatic substitution can be employed as a quick and straightforward way to synthesize these building blocks. While many methods to derivatize fluoroarenes exist that use heteroatom centered nucleophiles, there are fewer methods that use carbon centered nucleophiles, and of those many are poorly defined. This work presents the SNAr reaction of nucleophiles generated from nitroalkanes with a variety of fluorinated arenes. Given that the products are versatile, accessing polyfluorinated arene building blocks in substantial scale is important. This method is highly regioselective, and produces good to moderate yields on a large scale, sans chromatography, and thus fulfills this need. In addition, the regioselectivity of the addition was probed using both DFT calculations and experimentally via halogen exchange.

SNAr catalysis enhanced by an aromatic donor-acceptor interaction; facile access to chlorinated polyfluoroarenes

Selective catalytic S_NAr reaction of polyfluoroaryl C-F bonds with chloride is shown. Stoichiometric TMSCl makes the reaction exergonic and allows catalysis, which involves ground state elevation of chloride, aromatic donor-acceptor interactions, and stabilization of the Meisenheimer complex. Traditional cross-coupling of the products is now possible and demonstrates the utility.

Photocatalyst size controls electron and energy transfer: selectable E/Z isomer synthesis via C-F alkenylation

Photocatalytic alkene synthesis can involve electron and energy transfer processes. The structure of the photocatalyst can be used to control the rate of the energy transfer, providing a mechanistic handle over the two processes. Jointly considering catalyst volume and emissive energy provides a highly sensitive strategy for predicting which mechanistic pathway will dominate. This model was developed en route to a photocatalytic Caryl-F alkenylation reaction of alkynes and highly-fluorinated arenes as partners. By judicious choice of photocatalyst, access to E- or Z-olefins was accomplished, even in the case of synthetically challenging trisubstituted alkenes. The generality and transferability of this model was tested by evaluating established photocatalytic reactions, resulting in shortened reaction times and access to complimentary Z-cinnamylamines in the photocatalytic [2 + 2] and C-H vinylation of amines, respectively. These results show that taking into account the size of the photocatalyst provides predictive ability and control in photochemical quenching events.

Visible Light Photocatalysis for the Generation and Use of Reactive Azolyl and Polyfluoroaryl Intermediates

Photocatalysis offers several mechanistically unique pathways that are not rivaled by mainstream catalysis. Primarily, the ability to convert photochemical energy into single electron oxidation and reduction events provides a new dimension for chemists to consider when choosing how to activate a molecule or approach a complex synthesis. Since most organic molecules do not absorb light in the visible region, they are impervious to direct visible light photochemistry, which provides an opportunity for photocatalysis in which a visible light absorbing compound can serve as a mediator. In this Account, we discuss the consequences of catalyst mediated, photoinduced electron transfer to several classes of reducible arenes. While the bulk of the work discussed within this Account utilizes iridium-based photocatalysts, in principle the chemistry is not limited to this class of photocatalyst, and the principles should be more general. Instead, this Account focuses largely on the consequences of single electron transfer to poly- and perfluorinated arenes and 2-halo azoles. Electron transfer converts these stable molecules into reactive intermediates whose behavior often depends entirely on the identity of the halogen that undergoes substitution. The result is both diverse chemistry and an alternative way of thinking about the chemical reactivity of these motifs. Specifically, we discuss our efforts and those of others to develop strategies for the generation of radicals or radical anions from perfluoroarenes and azoles and the behavior of these intermediates as implied by reactions in which they participate. The divergent pathway is illustrated by 2-bromoazoles, which yield azolyl radicals and can be utilized for addition to π-bonds, while use of the 2-chloroazole substrate leads to an entirely different reaction profile. Under the appropriate reaction conditions, the reactive and transient intermediates are useful coupling partners and often provide unrivaled access to new chemical space. The odd electron species can form challenging bonds with minimal prefunctionalization of the coupling partner. For instance, some of the intermediates can be utilized for C-H functionalizations to selectively make crowded amines or to synthesize biarenes substituted at every ortho position. While photocatalysis is not the only manner of accomplishing electron transfer, the catalytic generation of the reactive species in which the concentration of the transient odd electron species is kept low, provides a synthetic handle that can be used to improve reaction outcomes. This is elegantly demonstrated in a number of examples in which redox sensitive groups located on substrates survive the reaction. In addition, the underlying basic concepts associated with radical anion fragmentation are reviewed and provide the backdrop for discussion throughout the Account.

Dual C-F, C-H Functionalization via Photocatalysis: Access to Multifluorinated Biaryls

Multifluorinated biaryls are challenging to synthesize and yet are an important class of molecules. Because of the difficulty associated with selective fluorination, this class of molecules represent a formidable synthetic challenge. An alternative approach to selective fluorination of biaryls is to couple an arene that already possesses C-F bonds in the desired location. This strategy has been regularly utilized and relies heavily on traditional cross-coupling strategies that employ organometallics and halides (or pseudohalides) in order to achieve the coupling. Herein we report conditions for the photocatalytic coupling via direct functionalization of the C-F bond of a perfluoroarene and C-H bond of the other arene to provide an expedient route to multifluorinated biaryls. The mild conditions and good functional group tolerance enable a broad scope, including access to the anti-Minisci product of basic heterocycles. Finally, we demonstrate the value of the C-F functionalization approach by utilizing the high fluorine content to systematically build complex biaryls containing between two and five Caryl-F bonds via the synergistic use of photocatalysis and SNAr chemistry.

Photocatalytic C-F Reduction and Functionalization

Functionalized polyfluorinated aromatics have become an important group of molecules for pharmaceutical and industrial applications. However, facile access to such valuable molecules remains an unmet challenge. In this review, we present and discuss photocatalytic C-F functionalization, which is emerging as a straightforward and operationally simple path to access partially fluorinated aromatics.

Photocatalytic C-F alkylation; facile access to multifluorinated arenes

C-F functionalizations that provide C-C bonds are challenging synthetic transformations, due in part to the large C-F bond strength, short bond length, nonpolarizable nature, the production of fluoride, and the regioselectivity-in the case of multifluorinated substrates. However, commercially available highly fluorinated arenes possess great synthetic potential because they already possess the C-F bonds in the desired locations that would be difficult to selectively fluorinate. In order to take advantage of this potential, selective C-F functionalizations must be developed. Herein, we disclose conditions for the photocatalytic reductive alkylation of highly fluorinated arenes with ubiquitous and unactivated alkenes. The mild reaction conditions provide for a broad functional group scope, and the reaction is remarkably efficient using just 0.25 mol% catalyst. Finally, we demonstrate the utility of the strategy by converting highly fluorinated arenes to elaborate (hetero)arenes that contain 2-5 Caryl-F bonds via synergistic use of photocatalysis and SNAr chemistry.

Selective perfluoro- and polyfluoroarylation of Meldrum's acid

This work describes the facile and mono-selective per- and polyfluoroarylation of Meldrum's acid to generate a versatile synthon for highly fluorinated α-phenyl acetic acid derivatives, which provide straightforward access to fluorinated building blocks. The reaction takes place quickly, and most products were isolated without the need for chromatography. Importantly, this method provides an alternative strategy to access α-arylated Meldrum's acids, which avoids the need for aryl-Pb(IV) salts or diaryliodonium salts. Furthermore, we demonstrate the synthetic versatility and utility of the Meldrum's acid products by subjecting our products to several derivatizations of the Meldrum's acid products as well as photocatalytic hydrodefluorination.

Facile synthesis of Z-alkenes via uphill catalysis

Catalytic access to thermodynamically less stable Z-alkenes has recently received considerable attention. These approaches have relied upon kinetic control of the reaction to arrive at the thermodynamically less stable geometrical isomer. Herein, we present an orthogonal approach which proceeds via photochemically catalyzed isomerization of the thermodynamic E-alkene to the less stable Z-isomer which occurs via a photochemical pumping mechanism. We consider two potential mechanisms. Importantly, the reaction conditions are mild, tolerant, and operationally simple and will be easily implemented.

Photocatalytic hydrodefluorination: facile access to partially fluorinated aromatics

Polyfluorinated aromatics are essential to materials science as well as the pharmaceutical and agrochemical industries and yet are often difficult to access. This Communication describes a photocatalytic hydrodefluorination approach which begins with easily accessible perfluoroarenes and selectively reduces the C-F bonds. The method allows facile access to a number of partially fluorinated arenes and takes place with unprecedented catalytic activity using a safe and inexpensive amine as the reductant.

Feasibility of localized immunosuppression: 3. Preliminary evaluation of organosilicone constructs designed for sustained drug release in a cell transplant environment using dexamethasone

As part of our ongoing effort to develop biohybrid devices for pancreatic islet transplantation, we are interested in establishing the feasibility of a localized immune-suppressive approach to avoid or minimize the undesirable side effects of existing systemic treatments. Since biohybrid devices can also incorporate biocompatible scaffold constructs to provide a support environment for the transplanted cells that enhances their engraftment and long-term function, we are particularly interested in an approach that would use the same three-dimensional construct, or part of the same construct, to also provide sustained release of therapeutic agents to modulate the inflammatory and immune responses locally. Within this framework, here, we report preliminary results obtained during the investigation of the suitability of organosilicone constructs for providing sustained localized drug release using small, matrix-type polydimethylsiloxane (PDMS) disks and dexamethasone as a model hydrophobic drug. Following a short burst, long-term steady sustained release was observed under in vitro conditions at levels of 0.1-0.5 microg/day/disk with a profile in excellent agreement with that predicted by the Higuchi equation. To verify that therapeutic levels can be achieved, suppression of LPS-induced activation has been shown in THP-1 cells with disks that have been pre-soaked for up to 28 days. These preliminary results prove the feasibility of this approach where an integral part of the biomaterial construct used to enhance cell engraftment and long-term function also serves to provide sustained local drug release.

Transition metal-catalyzed decarboxylative allylation and benzylation reactions

A review. Transition metal catalyzed decarboxylative allylations, benzylations, and interceptive allylations are reviewed.

Stereospecific decarboxylative allylation of sulfones

Allyl sulfonylacetic esters undergo highly stereospecific, palladium-catalyzed decarboxylative allylation. The reaction allows the stereospecific formation of tertiary homoallylic sulfones in high yield. In contrast to related reactions that proceed at -100 degrees C and require highly basic preformed organometallics, the decarboxylative coupling described herein occurs under mild nonbasic conditions and requires no stoichiometric additives. Allylation of the intermediate alpha-sulfonyl anion is more rapid than racemization, leading to a highly enantiospecific process. Density functional theory calculations indicate that the barrier for racemization is 9.9 kcal/mol, so the barrier for allylation must be <9.9 kcal/mol.

Synthesis of Chiral Nonracemic Tertiary α-Thio and α-Sulfonyl Acetic Esters via S(N)2 reactions of Tertiary Mesylates

Syntheses of enantioenriched sulfides and sulfones via substitution of tertiary mesylate with thiolate nucleophile with modest to excellent success.

Decarboxylative allylation using sulfones as surrogates of alkanes

Alpha-sulfonyl functional groups are traceless activating groups that facilitate catalytic decarboxylative allylations in high yield yet can be cleaved to allow the synthesis of simple allylated alkanes. Substrate studies suggest that decarboxylation to form an alpha-sulfonyl anion is rate-limiting. Furthermore, the anion is formed regiospecifically under formally neutral conditions.

Incubation of European yew (Taxus baccata) with white-tailed deer (Odocoileus virginianus) rumen fluid reduces taxine A concentrations

Yew ( Taxus baccata) foliage was co-incubated with rumen fluid (RF) taken from fistulated cattle (Bos taurus), anesthetized white-tailed deer (Odocoileus virginianus) and O. virginianus killed by bow hunters. The first trial with live deer resulted in statistically significant 59% reduction of taxine A by deer RF and no reduction by cattle RF. The second intubation trial, in which half the samples were stopped after 12 h, resulted in slightly less taxine A reduction by deer (46%) and 12% reduction by cattle RF. RF obtained by hunters eQuipped with thermos bottles and trained to collect RF immediatey upon field dressing their deer caused the most (88-96%) taxine A destruction: cattle RF reduced 68-88% the toxin. Obtaining RF from freshly killed deer was less expensive and more consistently successful than taking RF by intubation of anesthetized deer. The greater ability of white-tailed deer RF to detoxify yew taxines may not entirely explain the advantage white-tailed deer have over cattle to surviveyew ingestions without toxic effects.