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Issue 5, 2013
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Rapid and selective spiro-cyclisations of O-centred radicals onto aromatic acceptors

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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. 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.

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

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Publication details

The article was received on 21 Feb 2013, accepted on 14 Mar 2013 and first published on 15 Mar 2013


Article type: Edge Article
DOI: 10.1039/C3SC50500F
Citation: Chem. Sci., 2013,4, 2028-2035
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    Rapid and selective spiro-cyclisations of O-centred radicals onto aromatic acceptors

    R. T. McBurney, A. Eisenschmidt, A. M. Z. Slawin and J. C. Walton, Chem. Sci., 2013, 4, 2028
    DOI: 10.1039/C3SC50500F

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