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UBC Theses and Dissertations

Radical fluorination methods for the synthesis of aryl mono-, di-, and tri- fluoromethyl ethers Leung, Joe Cho Tak


New reagents for selective radical fluorine transfer have been identified and utilized to develop two novel photochemical reactions to access fluorinated methoxy arenes. I have discovered that SelectfluorTM can be employed as a radical fluorinating agent, leading to the development of a photochemical methodology (in aqueous alkaline SelectfluorTM solutions containing 2-aryloxyacetic acids) for the synthesis of aryl fluoromethyl, difluoromethyl, and trifluoromethyl ethers. In the second reaction developed, acetone N-fluorobenzensulfonimide solutions containing 2-aryloxyacetic acids will promote a different, milder, photosensitized decarboxylative fluorination reaction capable of delivering more electron rich aryl fluoromethyl ethers, and aryl difluoromethyl ethers. Density Functional Theory calculations support the assertion that radical intermediates are involved in fluorination. Alkoxyl radical reactions have also been investigated. I have found that the rate of alkoxyl 5-exo cyclization onto a silyl enol ether is only marginally faster than cyclization onto a trisubstituted alkene. The assumption that secondary and primary alkoxyl radicals display similar cyclization behaviour was proven unsound, and primary alkoxyl 5-exo cyclization onto a simple terminal alkene is likely faster than published rates. Alkoxyl radical 1, 5-hydrogen atom transfer was studied in the context of a radical relay cyclization methodology. I have demonstrated that primary, secondary and tertiary alkoxyl radicals may be successfully employed in the relay cyclization of 5 (5-exo), and 6 (6-endo) membered carbocyclic rings.

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