1.2- Dicarbonyl compounds from alkyl halides

When ethoxide is used as a base to abstract a-proton, it could react with the alkyl halide (Sn2) to form ether. However, the acid-base equilibrium with the diketone prefers the more stable, less basic enolate over the ethoxide, essentially consuming the ethoxide. Thus, the very stable enolates from 1,3-dicarbonyl compounds are able to undergo Sn2 reactions with alkyl halides without competition from the alkoxide catalyst. 

As an alternative to the discussed mechanism, Heck proposed the formation of a halide from the unsaturated compound and the acid present in the reaction mixture. This halide is then thought to react with Ni(CO)4 to form an alkyl nickel dicarbonyl halide according to equation (4b). 

---