Fig. 2: Scope of acyclic α-substituted β-keto esters.

Conditions: 1 (0.10 mmol), 2 (0.12 mmol), CuTC (10 mol%), Cat-3 (20 mol%), DCM (2.0 mL), at 0 °C for 30–48 h. b Conditions: 1 (0.10 mmol), 2 (0.12 mmol), CuTC (10 mol%), Cat-3 (25 mol%), MgSO4 (1.0 eq), DCM (2.0 mL), at 0 °C for 30–48 h. Boc tert-butoxycarbonyl.