Fig. 2: Substate scope of silyl enol ethers and BCBs.

aReaction 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. b6 h. c12 h. β-Me, methyl group syn to ethyl group; α-Me, methyl group anti to ethyl group. Naph 2-naphthyl, TIPS triisopropylsilyl, TES triethylsilyl, TBS tert-butyldimethylsilyl, TBDPS tert-butyldiphenylsilyl, o ortho, m meta, p para.