Practical method for the rhodium-catalyzed addition of aryl- and alkenylboronic acids to aldehydes

The arylation or alkenylation of aldehydes with boronic acids is convenient ly effected by a catalyst system comprising RhCl3 . 3H20 (1 mol %), the ste rically hindered imidazolium salt 2 (1 mol %), and a base. The N-heterocycl ic carbene 6 derived from 2 is believed to be the actual ligand to the cata lytically active rhodium species formed in situ. The method is compatible w ith various functional groups in both reaction partners and follows a non-c helation controlled pathway in additions to the Garner aldehyde 23.