Fig. 2: Survey of the catalysts for the asymmetric [3 + 2] annulation.

Reaction conditions: 1a (0.1 mmol), 2a (0.2 mmol), NaHCO₃ (1.5 equiv), C_X (2.0 mol%) or CuI (4 mol%)/L1-L7 (4 mol%), CF₃CH₂OH (1 mL), NH₄I (2 equiv), 40 ^oC, 24 h. NMR yields. The ee values were determined by HPLC on a chiral stationary phase.