Synthesis of 2-aryloxy butenoates by copper-catalysed allylic C-H carboxylation of allyl aryl ethers with carbon dioxide

Efficient synthesis of 2-aryloxy-3-butenoic acid esters by allylic C-H bond carboxylation of allyl aryl ethers with CO₂ has been achieved through deprotonative alumination with an aluminium ate compound (iBu₃Al(TMP)Li) followed by NHC-copper-catalysed carboxylation of the resulting aryloxy allylaluminum species. Functional groups such as halogens (F, Cl, Br, I), CF₃, amino, methylthio, silyloxy and hetero aromatic groups survived the reaction conditions. The regio- and stereoselective transformation (isomerization) of 2-aryloxy-3-butenoate products to (Z)-2-aryloxy-2-butenate isomers has also been achieved in the presence of a catalytic amount of DBU. These transformations thus constitute an efficient protocol for the divergent synthesis of both 2-aryloxy-3- and 2-butenonates from a single allyl aryl ether substrate using CO₂ as a C1 building block.