Lactone Radical Cyclizations and Cyclization Cascades Mediated by SmI₂–H₂O

Unsaturated lactones undergo reductive radical cyclizations upon treatment with SmI2–H2O to give decorated cycloheptanes in a single highly selective operation during which up to three contiguous stereocenters are generated. Furthermore, cascade processes involving lactones bearing two alkenes, an alkene and an alkyne, or an allene and an alkene allow “one-pot” access to biologically significant molecular scaffolds with the construction of up to four contiguous stereocenters. The cyclizations proceed by the trapping of radical anions formed by electron transfer reduction of the lactone carbonyl.