The first enantioenriched metalated nitrile possessing macroscopic configurational stability.

[structure: see text]. Magnesium-bromine exchange on enantiopure cyclopropyl bromonitrile 5 at -100 degrees C for 1 min followed by a D2O quench gives the deuterionitrile in 81% ee (retention); additional trapping experiments establish t(1/2)(rac) = 11.4 h at -100 degrees C. These experiments provide the first glimpse into the stereochemical aspects of Mg-Br exchange. The intermediate formed is the first metalated nitrile demonstrated to possess macroscopic configurational stability.