Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes
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Sensitised photolyses of ethoxycarbonyl oximes of aromatic and heteroaromatic ketones yielded iminyl radicals which were characterised by EPR spectrscopy. Iminyls with suitably placed arene or heteroarene acceptors underwent cyclisations yielding phenanthridine type products from ortho-additions. For benzofuran and benzothiophene acceptors, spiro-cyclisation predominated at low temperatures but thermodynamic control ensured ortho-products, benzofuro- or benzothieno-isoquinolines, formed at higher temperatures. Estimates by steady state kinetic EPR established that iminyl radical cyclisations onto aromatics took place about an order of magnitule more slowly than prototypical C-centred radicals. Cyclisation energetics were investigated by DFT computations which gave insights into factors influencing the two cyclisation modes.
Walton , J C & McBurney , R T 2013 , ' Interplay of ortho- with spiro-cyclisation during iminyl radical closures onto arenes and heteroarenes ' Beilstein Journal of Organic Chemistry , vol 9 , pp. 1083-1092 . DOI: 10.3762/bjoc.9.120
Beilstein Journal of Organic Chemistry
© 2013 McBurney and Walton; licensee Beilstein-Institut. This is an Open Access article under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The license is subject to the Beilstein Journal of Organic Chemistry terms and conditions: (http://www.beilstein-journals.org/bjoc).
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