Fig. 3: Scope of α,β‐alkynals 2.

Reaction conditions: 1 (0.3 mmol), 2 (1.05 mmol), NHC pre-catalyst D (15 mol%), Sc(OTf)₃ (20 mol%), DMAP (0.3 mmol), THF (7.5 mL), and 4 Å MS (300 mg) at 20 ^oC, for 3 days; the yield refers to the isolated yield based on 1; ee values were determined by HPLC.