The Halogen–Samarium Exchange Reaction: Synthetic Applications and Kinetics

Samarium stories: Aryl and heteroaryl iodides and bromides were converted to the corresponding samarium(III) reagents via halogen–samarium exchange reactions. In contrast to the previously reported aryllanthanum species, samarium reagents tolerate more functional groups. This is explained by the higher electronegativity of samarium, which leads to an organosamarium species with a less ionic carbon–metal bond.

Abstract

Fast I/Sm and Br/Sm exchanges take place when various aromatic or heterocyclic iodides and bromides are treated with nBu₂SmCl⋅4 LiCl and nBu₃Sm⋅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.

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