Anodic Electrochemistry: Curtin-Hammett Control, New Reaction Development, and the Use of Solar Power.

摘要

Because anodic oxidation reactions generate highly reactive radical cation intermediates while reversing the polarity of electron-rich functional groups, they provide intriguing new opportunities for bond formation. Such olefin coupling reactions allow us not only to synthesize new ring skeletons, but also to probe the chemistry of reactive radical cation intermediates.;In anodic oxidation reactions, radical cations formed at the anode can undergo reversible, intramolecular electron-transfer reactions. When this occurs, the product formed from the oxidation is governed by the Curtin-Hammett Principle. For example, intramolecular anodic olefin coupling reactions can be compatible with the presence of dithioketal protecting groups even though the dithioketal oxidizes at a lower potential than either of the groups participating in the cyclization. In this thesis, the scope of such Curtin--Hammett controlled reactions was extended to include carbon-carbon bond generation as well as the formation of medium sized rings. Suppression of unwanted side reactions was achieved with the use of alternative reaction conditions.;Using the Curtin-Hammett based approach, construction of the 5-7-5 core of the natural product artemisolide was attempted. Unfortunately, in this case the slow cyclization to form a seven-membered ring resulted in intermolecular trapping and elimination byproducts. This result led us to wonder if there were alternative modes of trapping an enol ether radical cation that would decrease its lifetime while still allowing for a slower cyclization to take place. To investigate this idea, new chemistry was developed which allows for the oxidation of substrates bearing nucleophiles at both ends of the enol ether initiating group. A number of model substrates were used to demonstrate the utility of this approach. In addition, the methodology allowed us to differentiate two ends of an olefin coupling cyclization product, thereby solving a synthetic challenge previously encountered in the group. Attempts to take advantage of this methodology to carry out the synthesis of artemisolide are currently underway.;Finally, we examined the use of photovoltaic cells to harness solar energy and power organic electrolyses in a sustainable fashion. A number of direct oxidation reactions, including olefin coupling reactions and amide oxidations, were studied using the photovoltaic cells. In all cases, yields of oxidation product were comparable to those obtained using the traditional electrochemical setup. In addition, preliminary studies were carried out to investigate the use of solar energy in indirect chemical oxidations. Initial evidence demonstrated that it is in fact possible to recycle chemical oxidants using solar energy, a finding that could dramatically impact the way oxidation reactions are carried out in the future.