Scheme 3. Cleavage of the carbamate group and determination of absolute configurations. Reaction conditions: (1) (i) TMSI (10 equiv.), CHCl₃, reflux; (ii) MeOH, reflux (only for 4u); and (2) for 5a: FcCOCl (1.1 equiv.), i-Pr₂NEt (3 equiv.), 4-dimethylaminopyridine (0.1 equiv.), CH₂Cl₂, 0 → 20 °C, 83% for 2 steps; for 5u: LiN(SiMe₃)₂ (1.2 equiv.), FcCOCl (1.2 equiv.), THF, –78 → –10 °C, 80% for 2 steps. TMSI = trimethylsilyl iodide; Fc = ferrocene. ^a Thermal ellipsoids at the 30% probability level, most H atoms are omitted for clarity.²⁶ .