Stereochemistry of the reactions of β-halothioethers with NaCN and AgCN

The S_N reactions of NaCN and AgCN with $\text{erythro}$ and $\text{threo}$-2-methylthio-3-halobutanes are reported. The stereochemistry of the resulting nitriles and isonitriles demonstrates that total retention in configuration has taken place in these processes. This disagrees with the accepted explanation for the regioselectivity of these reactions.