Discovery and optimization studies^a,b.

^aPerformed with 1a (0.2 mmol, 2 equiv.), 2a (0.1 mmol, 1 equiv.), Rh₂(esp)₂ (0.002 mmol, 1 mol%), and a fluoride source (3 equiv.) in CH₂Cl₂ (0.1 M).

^bYields are reported on the basis of ¹H-NMR analysis using anisole as the internal standard; branched/linear ratio was determined by ¹⁹F NMR analysis.

^cYields in parentheses are of (±)-3a/(±)-4/5. esp = α,α,α′,α′-tetramethyl-1,3-benzenedipropanoate.