Asymmetric hydrovinylation, the heterodimerization of a prochiral olefin with ethene gas, has been studied with respect to ligand effects to determine the underlying steric and electronic effects that led to high chemo-, regio-, and stereoselectivity in the formation of an α-benzylic stereogenic center. Fine tuning of the biaryl and amino moieties of Feringa’s phosphoramidite ligands yields structurally simpler, yet more efficient and selective ligands for asymmetric hydrovinylation of vinylarenes and acylic 1,3-dienes. The enantioselectivities and yields observed in the formation of the 3-arylbutenes are among the highest for all asymmetric catalytic processes reported to date for the synthesis of intermediates for the widely used anti-inflammatory 2-arylpropionic acids, including naproxen, ibuprofen, fenoprofen, and flurbiprofen.
Aryl bromides and iodides, in the presence of catalytic amounts of a palladacycle derived from acetophenone oxime and two equivalents of potassium acetate, react with ethene under ambient pressure (15-30 psi) to give the corresponding vinylarenes. The reactions work with both electron-deficient and electron-rich aryl compounds, and tolerate wide variety of common functional groups. Vinyl bromides lead to 1,3-dienes in moderate yields.