Rapid and selective spiro-cyclisations of O-centred radicals onto aromatic acceptors

Roy T. McBurney*, Annika Eisenschmidt, Alexandra M Z Slawin, John C. Walton

*Corresponding author for this work

Research output: Contribution to journalArticle

7 Citations (Scopus)

Abstract

Substituted benzyloxycarbonyloxyl radicals were generated by sensitised photolyses of benzyl oxime carbonates. EPR spectroscopy showed they ring closed exclusively by spiro-cyclisation onto the ipso-C-atoms of the aromatic rings. β-Scission of the alkoxycarbonyloxyls to CO2 and benzyloxyl radicals increasingly competed and became dominant above 270 K. The first rate parameters for spiro-cyclisations of O-centred radicals onto aromatics were obtained by the steady-state kinetic EPR method. Pentafluoro-substitution of the ring substantially reduced the spiro-cyclisation rate. Activation barriers of the spiro-cyclisations were computed by DFT to be about half those of the alternative ortho-cyclisations. Consideration of the TS structures suggested the preference for spiro- over ortho-cyclisation resulted from better overlap of the oxyl SOMO with the aromatic π-system during spiro closure.

Original languageEnglish
Pages (from-to)2028-2035
Number of pages8
JournalChemical Science
Volume4
Issue number5
DOIs
Publication statusPublished - May 2013
Externally publishedYes

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    McBurney, R. T., Eisenschmidt, A., Slawin, A. M. Z., & Walton, J. C. (2013). Rapid and selective spiro-cyclisations of O-centred radicals onto aromatic acceptors. Chemical Science, 4(5), 2028-2035. https://doi.org/10.1039/c3sc50500f