Practical Method for the Rhodium-Catalyzed Addition of Aryl- and Alkenylboronic Acids to Aldehydes

The arylation or alkenylation of aldehydes with boronic acids is conveniently effected by a catalyst system comprising RhCl3⋅3 H2O (1 mol %), the sterically hindered imidazolium salt 2 (1 mol %), and a base. The N-heterocyclic carbene 6 derived from 2 is believed to be the actual ligand to the catalytically active rhodium species formed in situ. The method is compatible with various functional groups in both reaction partners and follows a non-chelation controlled pathway in additions to the Garner aldehyde 23