Reaction Steps
To a stirred suspension of Dess-Martin periodinane reagent (6.60 g, 15.5 mmol) in anhydrous CH2Cl2 (100 mL) was added compound 2 (3.86 g, 13.4 mmol). The mixture was stirred at room temperature for 18 hours, poured into water, and extracted with ethyl acetate. The organic layer was washed several times with water, dried (MgSO4), and evaporated to give an oily residue which slowly crystallized on cooling (3.67 g, 95%). TLC indicated high purity of the obtained ketone 3 which could be used in the next step without further purification. Analytical sample was obtained by recrystallization from hexane. 3: m.p. 92-95° C.; 1H NMR (400 MHz, CDCl3) δ0.040 and 0.133 (3H and 3H, each s, 2×SiCH3), 0.895 (9H, s, Si-t-Bu), 2.15 (1H, dd, J=12.4, 10.4 Hz, 2α-H), 2.42 (1H, d, J=12.5 Hz, 8α-H), 2.54 (1H, ddd, J=12.4, 9.0, 3.9 Hz, 2β-H), 2.86 (1H, ddd, J=12.5, 6.7, 3.9 Hz, 8β-H), 4.54 (1H, dd, J=10.4, 9.0 Hz, 3β-H), 4.73 (1H, d, J=6.7 Hz, 5α-H); 13C NMR (125 MHz) δ−5.6 (Si—CH3), −4.8 (Si—CH3), 18.2 [C(CH3)3], 25.6 [C(CH3)3], 42.3 (C8), 43.0 (C2), 70.3 (C3), 71.8 (C1), 78.7 (C5), 177.1 (C═O), 202.4 (C4); MS (EI) m/z (relative intensity) no M+, 271 (M+−CH3, 4), 229 (92), 201 (28), 157 (100); HRMS (ESI) exact mass calcd for C9H13O5Si (M+−t-Bu) 229.0532, measured 229.0539; Anal. Calcd for C13H22O5Si×H2O: C, 51.29, H, 7.95. Found: C, 51.09, H, 7.90.
