Samarium iodide-mediated C–C bond formation in the total synthesis of natural products

Since its introduction by Kagan more than 40 years ago, samarium(ii) iodide (SmI2; Kagan’s reagent) has found copious applications in organic synthesis. Its inherent strong reducing ability, together with external additives, enable tunable reactivity and endow SmI2 with powerful reactivity and impressive chemoselectivity. As a result, SmI2 has been broadly applied in a wide range of useful transformations, especially those involving C–C bond formation, in which both radical and ionic pathways could be selectively accessible. In the total synthesis of natural products, the versatility of SmI2 renders it more appealing than other single-electron reductants, particularly when used in key steps at the late stages of synthetic routes. Moreover, its ability to reach previously unattainable C–C bond disconnections accelerates the development of new synthetic strategies. In this Review, we highlight selected examples of SmI2-mediated C–C bond formation in the total synthesis of natural products reported from 2014 to 2021.