Kelli A. Ogawa

Organocatalyzed anodic oxidation of aldehydes.

A method for the catalytic formation of electroauxiliaries and subsequent anodic oxidation has been developed. The process interfaces N-heterocyclic carbene-based organocatalysis with electro-organic synthesis to achieve direct oxidation of catalytically generated electroactive intermediates. We demonstrate the applicability of this method as a one-pot conversion of aldehydes to esters for a broad range of aldehyde and alcohol substrates. Furthermore, the anodic oxidation reactions are very clean, producing only H(2) gas as a result of cathodic reduction.

Metal-Free Ring-Opening Metathesis Polymerization

We have developed a method to achieve ring-opening metathesis polymerization (ROMP) mediated by oxidation of organic initiators in the absence of any transition metals. Radical cations, generated via one-electron oxidation of vinyl ethers, were found to react with norbornene to give polymeric species with microstructures essentially identical to those traditionally obtained via metal-mediated ROMP. We found that vinyl ether oxidation could be accomplished under mild conditions using an organic photoredox mediator. This led to high yields of polymer and generally good correlation between M(n) values and initial monomer to catalyst loadings. Moreover, temporal control over reinitiation of polymer growth was achieved during on/off cycles of light exposure. This method demonstrates the first metal-free method for controlled ROMP.

Organocatalyzed Anodic Oxidation of Aldehydes to Thioesters

A method has been developed for the direct conversion of aldehydes to thioesters via integration of organocatalysis and electrosynthesis. The thiazolium precatalyst was found to facilitate oxidation of thiolate anions, leading to deleterious formation of disulfide byproducts. By circumventing this competing reaction, thioesters were obtained in good-to-excellent yields for a broad range of aldehyde and thiol substrates. This approach provides an atom-efficient thioesterification that circumvents the need for stoichiometric exogenous oxidants, high cell potentials, or redox mediators.