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Catalyst‐Free Photoredox Addition–Cyclisations: Exploitation of Natural Synergy between Aryl Acetic Acids and Maleimide
Author(s) -
Manley David W.,
Mills Andrew,
O'Rourke Christopher,
Slawin Alexandra M. Z.,
Walton John C.
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201304929
Subject(s) - maleimide , chemistry , photochemistry , catalysis , spectroscopy , radical , aryl , electron paramagnetic resonance , reactive intermediate , nuclear magnetic resonance spectroscopy , organic chemistry , alkyl , physics , nuclear magnetic resonance , quantum mechanics
Suitably functionalised carboxylic acids undergo a previously unknown photoredox reaction when irradiated with UVA in the presence of maleimide. Maleimide was found to synergistically act as a radical generating photoxidant and as a radical acceptor, negating the need for an extrinsic photoredox catalyst. Modest to excellent yields of the product chromenopyrroledione, thiochromenopyrroledione and pyrroloquinolinedione derivatives were obtained in thirteen preparative photolyses. In situ NMR spectroscopy was used to study each reaction. Reactant decay and product build‐up were monitored, enabling reaction profiles to be plotted. A plausible mechanism, whereby photo‐excited maleimide acts as an oxidant to generate a radical ion pair, has been postulated and is supported by UV/Vis. spectroscopy and DFT computations. The radical‐cation reactive intermediates were also characterised in solution by EPR spectroscopy.