A rare, ruthenium‐catalyzed, oxazolinlyl assistedC−Hfunctionalization and three‐componentcascadecyclization for the synthesis of isoquinolinones via a metal‐carbenemigratoryinsertion is reported. The transformation is unique since it involves the formation of multiple bonds in onepot via C−Hfunctionalization and ring opening of oxazolines. Detailed mechanistic investigations reveal interesting