500348-96-9Relevant academic research and scientific papers
Catalyst-free photoredox addition-cyclisations: Exploitation of natural synergy between aryl acetic acids and maleimide
Manley, David W.,Mills, Andrew,O'Rourke, Christopher,Slawin, Alexandra M. Z.,Walton, John C.
, p. 5492 - 5500 (2014/05/20)
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. UVA photolyses of aryloxy-, arylthio- and arylamino-acetic acids with maleimide yield oxa-, thia- and aza-tricyclo pyrroledione derivatives in the absence of a photoredox catalyst (see scheme). An intriguing mechanism has been proposed and has been supported and supplemented by NMR monitoring experiments, DFT computations and UV/Vis and EPR spectroscopy.
