First methoxycarbonylation of the renewable β-myrcene: high selectivity through reduced isomerisation

Abstract

A direct route from a renewable material to odoriferous methyl esters is presented with the first methoxycarbonylation of the monoterpene β-myrcene. A simple homogeneous catalyst system of Pd(OAc)₂ and the bidentate ligand 1,4-bis(diphenylphosphino)butane (DPPB) in combination with low amounts of inexpensive acetic acid as an activator leads to a mixture of four isomers with a yield of 61%. The challenge of myrcene isomerisation induced through the necessary reaction conditions was overcome by systematic reaction optimisation. As an important parameter for the success of this reaction, the ester/isomer ratio was defined and improved during the research process. The atom economic reaction which uses the inexpensive bulk chemicals carbon monoxide and methanol could be upscaled to a multigram scale without the loss of activation.