Ligand-Controlled Palladium-Catalyzed Decarboxylative Heck Coupling for Regioselective Access to Branched Olefins

A highly chemo- and regioselective decarboxylative Heck-type coupling of carboxylic acids and terminal olefins has been developed using a catalytic system composed of Pd(OAc) 2 in the presence of phosphine-sulfonamido ligands. Using the bulky ligand L1 leads to high selectivity for 1,1-disubstituted (branched; b) olefins that are generally difficult to obtain. The influence of all relevant reaction parameters was evaluated using a combination of design of experiments and one factor at a time optimization. The coupling of dimethoxy-benzoic acid with various olefinic substrates gave the corresponding branched olefins with excellent regioselectivity (b/l up to 42:1) in up to 80% isolated yields. In contrast, using the less bulky ligand L2 results in the inverse regioselectivity leading to the 1,2-disubstituted (linear; l) product again in high yield of 86% (b/l = 1:26). Detailed investigation of the mechanistic pathways by DFT calculations reveals that the sterically demanding aryl substituent at the sulfonamide group of ligand L1 favors the pathway via 1,2-insertion with an energy preference of 4.4 kcal/mol, thus furnishing the 1,1-disubstituted branched olefins. In contrast, the 2,1-insertion reaction is advantageous by 1.3 kcal/mol for the analogous less bulky ligand L2 leading to the linear products.