... Journal of the American Chemical ... J. Am. Chem. Soc. ... Table 2. a Reactions were performed in dry CH 2 Cl 2 at —20 °C with 1.5 equiv of 4 using 10 mol % of Ga(O-iPr) 3 /(S,S)-2d and 9.5 mol % of Yb(OTf) 3 mixture. b Isolated yield after purification by column chromatography. ...