Palladium‐catalyzed thioesterifications of (aza)indole‐tethered aryl iodides, Mo(CO)6, and sulfonyl chlorides are reported. A series of C2 thioester‐group substituted indoline‐fused ring compounds are efficiently constructed using intramolecular Heck‐cyclization and carbonylation chemistry involving N‐(2‐iodobenzoyl)indole. The salient features of this three‐component cascade sequence include the use of solid Mo(CO)6 as the carbon monoxide source and good functional group tolerance.