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Domino Fragmentations in Traceless Directing Groups of Radical Cascades: Evidence for the Formation of Alkoxy Radicals via C–O Scission

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journal contribution
posted on 15.06.2016, 00:00 by Trevor Harris, Gabriel dos Passos Gomes, Ronald J. Clark, Igor V. Alabugin
Direct evidence for the formation of alkoxy radicals is reported in radical cascades using traceless directing groups. Despite the possibility of hydrogen abstraction in the fragmenting step, followed by loss of R-OH, β-scission is preferred for the formation of alkoxy radicals. For the first time, the C-O radical was intermolecularly trapped using a silyl enol ether. Various C–X fragmenting groups were explored as possible traceless directing groups for the preparation of extended polyaromatics. Computational evidence shows that a combination of aromatization, steric and stereoelectronic effects assists the fragmentation to alkoxy radicals. Additionally, a new through-space interaction was discovered between O and Sn in the fragmentation as a specific transition state stabilizing effect.