Exploiting Sm(ii) and Sm(iii) in SmI2-initiated reaction cascades: application in a tag removal–cyclisation approach to spirooxindole scaffolds

A tag removal-cyclisation sequence is described that is initiated by reduction using a Sm(II) species and completed by a Sm(III) Lewis acid that is formed in an earlier stage. Therefore, the reaction cascade utilises both oxidation states of a samarium reagent in discrete steps and allows access to privileged, pyrrolidinyl-spirooxindole scaffolds and analogues inspired by the anti-cancer natural product spirotryprostatin A.