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Reagents and conditions: (a) TMSOTf, CH2Cl2, molecular sieves 4 Å, −5 °C, 34% for 8α, 14% for 8β, 15% for 9α, 7% for 9β, 80% for 11; (b) 99% TFA, CH2Cl2, 0 °C, 83% for 9α, 88% for 14; (c) TBAF, THF, rt, 98% for 12, 97% for 15; (d) H2 (1 atm), 10% Pd–C, MeOH, then 0.01 M aq NaOH, rt, 90% for 12→13, 95% for 15→13, 79% for 16→17; (e) NaIO4–SiO2, CH2Cl2, −10 °C, then NaBH4, MeOH, 0 °C, 34%.
