Heck arylation of acrolein acetals using the 9-bromoanthracene: A case of study

The influence of several parameters on the selectivity of the palladium catalysed Heck coupling of 9-bromoanthracene with acrolein acetals was studied. While the ester is the quasi exclusive product when only a base (i.e. NaOAc, K2CO3, etc.) is added in the medium, the presence of halide abstracting agent such as thallium or silver salts decreases noticeably the selectivity towards the ester. On the other hand, the addition of n-Bu4NOAc yields to the formation of the aldehyde with up to 74% selectivity. The presence of water was found to play a significant role not only on the rate but also on the selectivity of the reaction. A comprehensive mechanism is proposed outlining the influence of each additive, particularly on the selectivity of the reaction.

The reaction conditions influence drastically the selectivity of the coupling of 9-bromoanthracene with acrolein acetals. Optimising the reaction conditions allowed the selective synthesis of the saturated esters or, on the other hand, of the unsaturated aldehydes. A global mechanism is proposed to outline the influence of additives.Figure optionsDownload as PowerPoint slide