In a glovebox, an oven dried screw-capped 2 mL vial was charged with a magnetic stir bar, Ni(COD)2 (10 μmol), carbene ligand Me IPr tBu (10 μmol), degassed (free pump thaw) THF (0.1 mL) was then added and the catalyst mixture was stirred at room temperature for 10 min, during which a red black solution is formed. Deuterated ketone D-1i (0.1 mmol degassed freeze pump thaw) and COD 2a (0.15 mmol degassed by freeze pump thaw) was then added successively.