Study On The Synthesis Of Coumarins Via PIDA/I₂-mediated Oxidative Cyclization Of Substituted Phenylacrylic Acids

Coumarin and its derivatives are widely distributed in natural products. Amongthe naturally occurring products,4-aryl coumarin derivatives, also known asneoflavonoids, have received considerable attention after they were reported toexhibit important biological properties such as cytotoxic, anti-HIV, antimalarial andantibacterial activities. Recently, more and more attention has been paid to thedevelopment of novel strategies for the synthesis of coumarin derivatives. Accordingto previous reported methods for C-O bond formation via hypervalent iodine reagents,we proposed a novel approach to synthesize a series of coumarins via trivalent iodineoxidative cyclization of phenylacrylic acid derivatives.Various of3,3-diarylacrylic acids were prepared from the correspondingbenzophenones via Horner-Wadsworth-Emmons reaction using triethylphosphonoacetate followed by saponification. A series of functionalized coumarinswere synthesized from substituted phenylacrylic acids via PIDA/I2-mediated andirradiation-promoted oxidative carbon-oxygen bond formation. The C-O bond isformed between the oxygen of the carboxyl group with an aromatic sp2carbon. Themain advantages of this method include mild reaction conditions, good functionalgroup tolerance and the transition-metal-free characteristic.A variety of functionalized coumarins were synthesized from substitutedphenylacrylic acids through this method. The structures of the compounds werecharacterized by1H&13C NMR spectra, LRMS and X-ray analysis. Mechanismsinvolving the reaction process were studied. In addition, one possible mechanism wasproposed.