Iron-catalyzed decarboxylative cross coupling reactions and palladium-catalyzed sp2-sp3 coupling of coumarins.

Abstract

The thesis details the development of a decarboxylative synthesis of aryl ethers using a relatively new Iron catalyst and a novel decarboxylative coupling of coumarins catalyzed by palladium. Aryl allyl carbonates underwent facile decarboxylative coupling in presence of a new iron catalyst. The allylation is found to be regioselective rather than regiospecific. This suggests that the allylation proceeds through π-allyl iron intermediates in contrast to related allylations of carbon nucleophiles that proceed via σ-allyl complexes. The reason we looked at iron as a catalyst was to offset the cost of expensive palladium catalyst usually used in these types of reactions. The second project involved allyl esters of 3-carboxylcoumarins, which underwent facile decarboxylative coupling at just 25−50 °C in moderate to good yields. This represents the first extension of decarboxylative C−C bond-forming reactions to the coupling of aromatics with sp3-hybridized electrophiles. Finally, the same concept can be applied to the sp2−sp3 couplings of pyrones and thiocoumarins. A variety of biologically important heteroaromatics can be readily functionalized without the need for strong bases or stoichiometric organometallics that are typically required for more standard cross-coupling reactions.