“On Water” Catalytic Aldol Reaction between Isatins and Acetophenones: Interfacial Hydrogen Bonding and Enamine Mechanism

Insulator-on-Conductor Fouling Amplifies Aqueous Electrolysis Rates

The chemical industry is a major consumer of fossil fuels. Several chemical reactions of practical value proceed with the gain or loss of electrons, opening a path to integrate renewable electricity into chemical manufacturing. However, most organic molecules have low aqueous solubility, causing green and cheap electricity-driven reactions to suffer from intrinsically low reaction rates in industry's solvent of choice: water. Here, we show that a strategic, partial electrode fouling with hydrophobic insulators (oils and plastics) offsets kinetic limitations caused by poor reactant solubility, opening a new path for the direct integration of renewable electricity into the production of commodity chemicals. Through electrochemiluminescence microscopy, we reveal for the oxidation of organic reactants up to 6-fold reaction rate increase at the "fouled" oil-electrolyte-electrode interface relative to clean electrolyte-electrode areas. Analogously, electrodes partially masked (fouled) with plastic patterns, deposited either photolithographically (photoresists) or manually (inexpensive household glues and sealants), outperform clean electrodes. The effect is not limited to reactants of limited water solubility, and, for example, net gold electrodeposition rates are up to 22% larger at fouled than clean electrodes. In a system involving a surface-active reactant, rate augmentation is driven by the synergy between insulator-confined reactant enrichment and insulator-induced current crowding, whereas only the latter and possibly localized decrease in iR drop near the insulator are relevant in a system composed of non-surface-active species. Our counterintuitive electrode design enhances electrolysis rates despite the diminished area of intimate electrolyte-electrode contact and introduces a new path for upscaling aqueous electrochemical processes.

Pushing Photochemistry into Water: Acceleration of the Di-π-Methane Rearrangement and the Paternó-Büchi Reaction "On-Water"

Two representative organic photoreactions, namely a bimolecular photocycloaddition and a monomolecular photorearrangement, are presented that are accelerated when the reaction is performed "on-water", that is, at the water-substrate interface with no solvation of the reaction components. According to the established models of ground-state reactions "on-water", the enhanced efficiency of the photoreactions is explained by hydrophobic effects (Paternó-Büchi reaction) or specific hydrogen bonding (di-π-methane rearrangement) at the water-substrate interface that decrease the energy of the respective transition state. These results point to the potential of this approach to conduct photoreactions more efficiently in an ecologically favorable medium.

The Ligand Free Palladium(II)-Catalyzed Regioselective 1,2-Addition of Enol Silanes to Quinones to Access 4-Hydroxy-4-(2-oxo-2-arylethyl)cyclohexadien-1-ones and Synthetic Applications

In contrast to the conventional 1,4-addition process, regioselective 1,2-addition of silyl enol ethers to quinones can now be achieved via a palladium(II) enolate pathway that provides access to 4-hydroxy-4-(2-oxo-2-arylethyl)cyclohexa-2,5-dien-1-one derivatives. This quinone alkylation protocol proceeds under mild reaction conditions at ambient temperature under open air and does not require either an external ligand for the palladium or the use of a base. Additionally, the cyclohexadienone products have been exploited as synthetic precursors for the construction of fused heteroaryl systems.

Water as the reaction medium in organic chemistry: from our worst enemy to our best friend

A review presenting water as the logical reaction medium for the future of organic chemistry. A discussion is offered that covers both the "on water" and "in water" phenomena, and how water is playing unique roles in each, specifically with regard to its use in organic synthesis.

Bio-inspired NHC-organocatalyzed Stetter reaction in aqueous conditions

The first bio-inspired N-Heterocyclic Carbene (NHC)-catalyzed Stetter reaction in aqueous medium is reported with benzaldehyde and chalcone as model substrates. A screening of azolium salts as precatalysts revealed the remarkable efficiency of synthetic thiazolium salt 8 (up to 90% conversion in pure water at 75 °C). The reaction was successfully extended to various simple aldehyde substrates. The effect of temperature was also investigated in order to extend the reaction to lower temperature allowing a potential application to sensitive biomolecules. This study highlighted the influence of both solvent and temperature on the 1,4-diketone 3/benzoin 4 ratio. New precatalysts 26 and 27 were designed and synthesized to explore a possible compartmentalization of the reaction in aqueous conditions. Owing to the use of inexpensive metal-free N-Heterocyclic Carbene (NHC) as a bioinspired catalyst, we anticipate that this green strategy in aqueous conditions will be attractive for bioconjugation of many biomolecule-type aldehydes and enone derivatives.

Construction of Benzothiophene or Benzothiopheno[2,3-e]azepinedione Derivatives via Three-Component Domino or One-Pot Sequences

An efficient three-component domino or one-pot strategy has been developed for the synthesis of medicinally important benzothiophene and benzothiopheno[2,3-e]azepinedione derivatives for the first time. Amine-promoted selective cleavage of C-S bond of thioisatin is the key step in this process. The reported methodology benefits from environmentally friendly solvent (H₂O), wide substrate scope, good functional group tolerance, and high reaction yields.