The use of oxidative cyclization with radical or radical ion intermediates is a potentially useful and efficient strategy to achieve the synthesis of novel heteroaromatic structures. Oxime ethers with built in aromatic groups have been shown to undergo a cyclization reaction in which the aromatic ring acts a nucleophile attacking the oxime ether radical cation. Using this same methodology, aromatic nucleophiles with built in heteroatoms could lead to potential new synthetic pathways of interesting and complicated heteroaromatic ring systems. To determine whether heteroaromatic rings can be used as nucleophiles under oxidative cyclization conditions, we prepared a series of benzaldehyde oximes and oxime ethers substituted with heteroaromatic rings containing nitrogen, oxygen, and sulfur. The purified oximes and oxime ethers were subjected to photooxidation processes in controlled conditions and were monitored by GC/MS and NMR for product formation. The result from these studies suggest that the oximes formed their parent aldehydes but did not show signs of cyclization. Several oxime ethers were found to yield what is believed to be a cyclized product via nucleophilic attack by the heteroaromatic ring on the nitrogen of the oxime ether. The most promising results were obtained with the thiophenyl derivatives of the oxime ethers. To further determine if the thiophenyl oxime ether derivatives did in fact cyclize, the reaction is being optimized so the product can be isolated and characterized. In the process of synthesizing the furanyl and thiophenyl oxime derivatives an unknown, possibly cyclized, side product is formed. These side products are being analyzed and characterized. The mechanistic pathway of this product formation is also being investigated.

Optimization and characterization of oxidative cyclization reactions of benzaldehyde oximes and oxime ethers with built-in heteroaromatic rings

253rd National Meeting (2017)

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