Electron Transfer Reactions in Organic Chemistry

My research group is developing new catalytic, chain, and stoichiometric chemistry based upon the cation radical intermediate. We have taken the view that the missing electron (hole) in a cation radical is a generalized catalytic entity, analogous to the proton, which is capable of supporting a wide variety of extremely fast, selective, and synthetically useful organic chemistry. The field of hole catalysis is currently undergoing rapid expansion, and already many relatively efficient examples of pericyclic and non-pericyclic chemistry have been established. Examples include Diels-Alder cycloaddition, cyclobutanation, cyclopropanation, epoxidation, hydrogenation, and vinylcyclobutane rearrangements.

In addition to developing new cation radical chemistry, our group has developed sensitive cation radical probes, which are capable of detecting even very short lived cation radical intermediates. These probes have recently been used to investigate a possible electron transfer mechanism for the metalloporphyrin catalyzed epoxidation of alkenes and should find application in analogous studies of enzyme catalyzed epoxidations. The growing appreciation of electron transfer (ET) mechanisms as a viable part of the mechanistic manifold has led to the suggestion of cation radical intermediates in a large number of organic reactions, and the probes will permit a more rigorous search for the proposed cation radicals.

We are currently investigating extension of the concept of hole catalysis to polymerization. The development of a cation radical propagation mechanism for polymerization would provide a fundamentally new mechanistic approach to polymerization and give access to a unique library of new polymer structures.

Cation radical reactions almost invariably involve electron transfer (more appropriately termed "hole transfer" in the present context) in one or more steps of the chain or catalytic cycle. As part of our continuing mechanistic and theoretical studies of cation radical reactions, we are studying the phenomenon of hole transfer in the context of hole catalytic chemistry.

An exciting new development in this laboratory is the development of a body of new anion radical cycloaddition chemistry, both intramolecular and intermolecular. Anion radical chain cycloaddition reactions initiated by electrochemical reduction, by persistent aromatic anion radicals, and by low-valent metal species are being explored. In the future, this group intends to develop a further novel method of cycloaddition polymerization, using anion radical cycloaddition chemistry.

Yang, J.; Felton,G.; Bauld, N.L.;Krische, M.J. "Chemically Induced Anion Radical Cycloaddition: Intramolecular Cyclobutanation of bis(Enones) via Homogeneous Electron Transfer." J. Am. Chem. Soc. (2004): .

Roh, Y.; Jang, H-Y.; Lynch, V.; Bauld, N.L.; Krische, M.J. "Anion Radical Chain Cycloaddition of Tethered Enones: Intramolecular Cyclobutanation and Diels-Alder Cycloaddition." Org. Lett. 4 (2002): 611-613.

Bauld, N.L.; Roh, Y. "New Polymer Structures and Polymerization Mechanisms Based Upon Cation Radical Cycloadditions." Current Organic Chemistry 6 (2002): 647-664.