Dropping the start temperature of the reaction from 0 °C to -20 °C was beneficial (Figure , Entry 6), but there was no benefit to further decreasing the temperature to -78 °C (Figure , Entry 7). To confirm the stereochemistry of 5, we prepared its acetate derivative, assigned the shifts of the salient protons using 2-D NMR spectroscopy, and saw a strong transannular nOe enhancement between these protons (see Supporting Information for further details).