The Halogen-Samarium Exchange Reaction: Synthetic Applications and Kinetics.

Fast I/Sm and Br/Sm exchanges take place when various aromatic or heterocyclic iodides and bromides are treated with nBu2 SmCl⋅4 LiCl and nBu3 Sm⋅5 LiCl, respectively. The resulting organosamarium reagents were efficiently quenched with aldehydes, ketones, and imines. Also, they undergo acylations when treated with N,N-dimethylamides leading to ketones. The rate of the Br/Sm exchange for a typical aryl bromide was determined and found to be 8.5×105 faster than the Br/Mg exchange, indicating that the rate of a metal-exchange is related to the ionic character of the carbon-metal bond and to the metal electronegativity.