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Rapid and Selective Spiro-Cyclisations of O-Centred Radicals onto Aromatic Acceptors

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John Christopher Walton, Roy Thomas McBurney, Annika Eisenschmidt, Alexandra Martha Zoya Slawin

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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. -Scission of the alkoxycarbonyloxyls to CO2 and benxyloxyl 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 -system during spiro closure
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Original languageEnglish
Pages (from-to)2028-2035
Number of pages8
JournalChemical Science
Volume4
Early online date15 Mar 2013
DOIs
StatePublished - Mar 2013

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