Cyclic nitriles: diastereoselective alkylations

reaction: see text] Diastereoselective alkylations of metalated conformationally locked 4-tert-butylcyclohexanecarbonitrile are highly diastereoselective with magnesium and copper counterions but only modestly diastereoselective with lithium as the counterion. Selective generation of diverse metalated nitriles is readily achieved through bromine-magnesium, -copper, and -lithium exchange reactions of the corresponding bromonitrile or, for lithium, by deprotonating the parent nitrile with lithium diethylamide. Collectively, high alkylation stereoselectivities correlate with the retentive alkylations of C-metalated nitriles, whereas N-lithiated nitriles alkylate with modest selectivity, reflecting minimal steric differences in the corresponding axial and equatorial electrophile trajectories.