Scheme 2.

Synthesis of 3a–b: (i) Raney Ni-Al alloy, 1% aq. KOH/water, 90°C, 2 h; (ii) L-Malic acid, H₂SO₄, HOAc, 140°C, 6 h (R=H); CH₃COCH₂COOC₂H₅, POCl₃, 100°C, 18 h (R=CH₃); (iii) CrO₃, HOAc, rt, 3 days; (iv) NaBH₄, CH₃OH, 1 h; (v) 2% H₂SO₄, reflux, 6–16 h; (vi) AD-mix-α (K₂OsO₄·2H₂O, K₃Fe(CN)₆, (DHQ)₂PHAL, K₂CO₃), t-butanol/H₂O 1:1, rt, 2–3 days; (vii) (S)-camphanic chloride, pyridine, DMAP, CH₂Cl₂, rt, 24 h.