Table 1. Optimization Studies^a.

^aPerformed at 0.1 mmol scale by addition of 1a and 2 over the Rh catalyst in CH₂Cl₂ at −50 °C during 30 min and then warmed to rt in 3 h.

^b1H NMR yields used CH₂Br₂ as an internal standard; a single diastereoisomer of 3a was observed (>20:1) in each entry, and 4a was obtained as an equimolecular mixture of four diastereoisomers.

^cNaHCO₃ was added (2 equiv). oct = octanoate. adc = 1-adamantylcarboxylate. esp = α,α,α′,α′-tetramethyl-1,3-benzenedipropanoate.