Krapcho's decarboxylation is a reaction involving esters with a electron-withdrawing group $\beta$ to the carbonyl group and halide ions. It is typically conducted with $\ce {LiCl}$ and $\ce {DMSO}$ at high temperatures. However, in one of Krapcho's original papers, $\ce {NaCN}$ was also used alongside $\ce {DMSO}$.
What interests me is the first step of the reaction which involves the nucleophilic subsitution, likely by an $\ce {S_N2}$ pathway, of the alkyl group of the ester functionality. This is seemingly weird as the $\ce {C-O}$ bond usually does not break unless in acid catalysis. This is the case for the cleavage of ethers using $\ce {HX}$. I suppose the use of $\ce {LiCl}$ was to allow the $\ce {Li^+}$ to coordinate to the oxygen atom, allowing the $\ce {C-O}$ bond to cleave more easily. Why is it that $\ce {NaCN}$ can also do the job?