Sometimes they disguise it. Tributyl(1-ethoxyvinyl)stannane is an organotin reagent used in Stille cross-coupling. Its useful cargo is a 1-ethoxyvinyl group. First, palladium helps transfer that fragment from tin to an aromatic or heteroaromatic molecule.
A brominated position can become: Ar-C(OEt)=CH2 That doesn't look like an acetyl group yet. Then add acid and water. The enol ether hydrolyzes to: Ar-COCH3 Now the hidden acetyl group has revealed itself. Why go through the disguise?
Global Chemical Database