James E. Jackson

Dissecting the Stereocontrol Elements of a Catalytic Asymmetric Chlorolactonization: Syn Addition Obviates Bridging Chloronium

We report absolute and relative stereochemistry of addition in enantioselective chlorolactonizations of 4-phenyl-4-pentenoic acid and its related t-butyl ester, catalyzed by (DHQD)2PHAL. Predominant syn addition of the chlorenium and the nucleophile across the olefin is observed. As shown by isotopic labeling, NMR spectroscopy, and derivative studies, the two new stereocenters formed by addition across the double bond are set independently and influenced by different factors. These findings suggest a stepwise process via an intermediate capable of lactone closure with either stereochemistry, in contradistinction to the more familiar scenario in which anti addition is dictated by a bridging chloronium ion intermediate.

A New Tool To Guide Halofunctionalization Reactions: The Halenium Affinity (HalA) Scale

We introduce a previously unexplored parameter—halenium affinity (HalA)– as a quantitative descriptor of the bond strengths of various functional groups to halenium ions. The HalA scale ranks potential halenium ion acceptors based on their ability to stabilize a “free halenium ion”. Alkenes in particular but other Lewis bases as well, such as amines, amides, carbonyls, and ether oxygen atoms, etc., have been classified on the HalA scale. This indirect approach enables a rapid and straightforward prediction of chemoselectivity for systems involved in halofunctionalization reactions that have multiple nucleophilic sites. The influences of subtle electronic and steric variations, as well as the less predictable anchimeric and stereoelectronic effects, are intrinsically accounted for by HalA computations, providing quantitative assessments beyond simple “chemical intuition”. This combined theoretical–experimental approach offers an expeditious means of predicting and identifying unprecedented reactions.

Alkali metals in silica gel (M-SG): A new reagent for desulfonation of amines

A novel method for the desulfonation of secondary amines is described. Alkali metals absorbed into nanostructured silica (M-SG) were found to be useful solid-state reagents for the desulfonation of a range of N,N-disubstituted sulfonamides. M-SG reagents are room-temperature-stable free-flowing powders that retain the chemical reactivity of the parent metal, decreasing the danger and associated cost of using reactive metals.

Solvent-dependent enantiodivergence in the chlorocyclization of unsaturated carbamates.

A remarkable solvent-controlled enantiodivergence is seen in the hydroquinidine 1,4-phthalazinediyl diether ((DHQD)2PHAL)-catalyzed chlorocyclization of unsaturated carbamates. Eyring plot analyses of this previously unreported reaction are used to probe and compare the R- and S-selective pathways. In the CHCl3/hexanes solvent system, the pro-R process shows a surprising increase in selectivity with increasing temperature. These studies point to a strongly solvent-dependent entropy-enthalpy balance between the pro-R and pro-S pathways.

From Molecules to the Crystalline Solid: Secondary Hydrogen‐Bonding Interactions of Salt Bridges and Their Role in Magnetic Exchange

Secondary hydrogen-bonding interactions have been exploited to construct layered magnetic solids based on amidinium–carboxylate salt bridges. The salt bridge is utilized as a supramolecular synthon to set the structural organization in a layered motif; it also serves as a spin communication element. The magnetic material shown in the accompanying figure is formed between 3-cyanobenzamidinium and 2,2,4,4-tetramethylpyrroline-N-oxyl-3-carboxylate.

TUNING DIHYDROGEN BONDS : ENHANCED SOLID-STATE REACTIVITY IN A DIHYDROGEN-BONDED SYSTEM WITH EXCEPTIONALLY SHORT H...H DISTANCES

Topochemical assembly of a covalent material can be achieved with the complex LiBH4 ⋅TEA (TEA=triethanolamine; section of structure shown), a dihydrogen-bonded system which has very short H⋅⋅⋅H contacts and high solid-state reactivity due to acidity enhancement in the OH groups by Li+ ion complexation.

Reciprocal Hydrogen Bonding–Aromaticity Relationships

Computed association energies and dissected nucleus-independent chemical shifts (NICS) document the mutual enhancement (or reduction) of intermolecular interactions and the aromaticity of H-bonded substrates. H-bonding interactions that increase cyclic 4n + 2 π-electron delocalization boost aromaticity. Conversely, such interactions are weakened when aromaticity is decreased as a result of more localized quinoidal π character. Representative examples of the tautomeric equilibria of π-conjugated heterocyclic compounds in protic solvents and other H-bonding environments also illustrate such H-bonding/aromaticity interplay.

A mild approach for bio-oil stabilization and upgrading: electrocatalytic hydrogenation using ruthenium supported on activated carbon cloth

Electrocatalytic hydrogenation (ECH) offers a new approach for bio-oil stabilization (a.k.a. partial upgrading). Water-soluble bio-oil, obtained by aqueous extraction of the liquid product of biomass pyrolysis, was hydrogenated using ECH at room conditions. A new electrocatalyst, ruthenium supported on activated carbon cloth, was used as the catalytic cathode. After electrocatalytic hydrogenation, aldehydes and ketones were reduced to the corresponding alcohols or diols, forms less prone to condensation chemistry. Carbon recovery into the liquid product, important when making liquid fuels from biomass, was more than 80%, while less than 0.1 wt% of the water-soluble bio-oil formed solid precipitate. The stability of the ECH-treated water-soluble bio-oil was checked via an accelerated aging test followed by size exclusion chromatography analysis and viscometry. Besides stabilization of bio-oil for subsequent fuel production, hydrogen and valuable diols were produced during ECH. Strategies to optimize the energy efficiency of this approach by altering the cell design, modifying the catalyst and adjusting the reaction conditions were also explored.

Birch reductions at room temperature with alkali metals in silica gel (Na2K-SG(I)).

Alkali metals in silica gel (the Na(2)K-SG(I) reagent) cleanly effect Birch reductions of substrates with at least two or more aromatic rings. The reaction conditions are alcohol-free, ammonia-free, and achieve excellent yields and high selectivities at room temperature.

Electrocatalytic upgrading of model lignin monomers with earth abundant metal electrodes

Guaiacol (2-methoxyphenol) and related lignin model monomers undergo electrocatalytic hydrogenolysis/hydrogenation (ECH) to cyclohexanol with RANEY® Nickel electrodes in aqueous solution. Aryl ether (C–O) bond cleavage is followed by reduction of the aromatic ring at ambient pressure and 75 °C. Related arene-OR cleavages occur at similar rates regardless of R-group size. Protons are supplied by anodic water oxidation on a stainless steel grid coated with cobalt-phosphate catalyst, inexpensively replacing the conventional platinum anode, and remaining viable in constant current electrolyses of up to 16 hours. The overall method addresses two key barriers to energy upgrading of low specific energy biomass into fuels and chemicals: deoxygenation and hydrogenation. By directly and simply coupling energy from renewable electricity into the chemical fuel cycle, ECH bypasses the complexity, capital costs and challenging conditions of classical H2 hydrotreating, and may help open the door to truly carbon-retentive displacement of fossil petroleum by renewables.