Low-Valent Rare Earth Reagents : Recent Progress

Samarium diiodide (SmI2) is widely employed as a useful single-electron reducing agent in organic synthesis because of its adequate reducing ability and suitable solubility in organic solvent such as THF. Although samarium diiodide itself can reduce aldehydes, ketones, alkyl bromides, and iodides, the reduction requires long period of heating and stirring. To enhance the reducing ability of SmI2, therefore, several unique methods have been developed recently, which include the addition of ligands, the combination with other metals, and photoactivation. This review deals with the recent advance in low-valent rare earth metal-assisted new reduction systems.