Table . Substate Scope of Silyl enolate and BCBs a a Reaction conditions: unless indicated otherwise, the reaction of silyl enol ether 1 (0.2 mmol), and BCB 2 (0.26 mmol) was carried out in DCM (2 mL) or toluene (2 mL) in the presence of Yb(OTf)3 (0.01 mmol) at room temperature for 2-4 h. The yield was of isolated and purified products. b 12 h. c 6 h.