Visible-light-promoted metal- and photocatalyst-free
radical cascade
cyclization of cinnamamides with α-oxocarboxylic acids is described
for sustainable synthesis of diverse pharmaceutically important dihydroquinolinone
scaffolds in one pot under mild conditions. The decarboxylative cascade
cyclization proceeded efficiently at room temperature without the
need for expensive photocatalysts such as Ir or Ru complexes, which
indicates the practicability and environmentally benign nature of
this protocol. Preliminary mechanistic studies reveal that the blue
LED irradiation efficiently cleaves the I–O bond of the hypervalent
iodine reagent PhI(O2CCOAr)2 formed through
ligand exchange between iodobenzene diacetate and arylglyoxylic acid
to initiate the cascade reaction. The synthetic value of this operationally
simple and energy-efficient method is further demonstrated by late-stage
functionalization of drug molecules in excellent yields.
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