Reaction Steps
Compound 2007 (0.0527 g, 0.079 mmol) in anhydrous THF (4 ml) under Ar was treated with tetrabutylammonium fluoride (TBAF) (0.237 ml, 1 M in THF, 0.237 mmol). The solution was stirred until no starting material remained by TLC. The solvent was removed in vacuo, the residue taken up in 5 ml CH2Cl2, washed with 5 ml aqueous saturated NaHCO3 solution, and the aqueous layer was extracted 2× with 5 ml CH2Cl2. The combined organic layers were dried over anhydrous MgSO4, filtered, and the solvent removed in vacuo. Flash chromatography (SiO2, 8:1 hexanes:EtOAc) gave compound 2008 (0.0395 g, 90%) as a white solid foam. 1H NMR (500 MHz, CDCl3) δ: 7.35-7.34 (m, 5H, benzyl Ar—H), 4.71-4.69 (m, 1H, THP ether methine H), 4.585 (d, J=11.8 Hz, 1/2H, benzyl-CH2), 4.58 (d, J=11.8 Hz, 1/2H, benzyl-CH2), 4.315 (d, J=12.0 Hz, 1/2H, benzyl-CH2), 4.29 (d, J=12.0 Hz, 1/2H, benzyl-CH2), 3.94-3.90 (m, 1H, THP OCH2), 3.62-3.58 (m, 3H, C-24 H & THP OCH2), 3.50-3.48 (m, 1H, C-3 H), 3.45 (s, 1H, 7-H), 0.92 (d, J=6.6 Hz, 3H, C-21 H), 0.81 (s, 3H, C-19 H), 0.63 (s, 3H, C-18 H) (Note: product is a mixture of diastereomers); IR (CHCl3) 3600, 2900 cm−1; MS (CI/isobutane) m/z 554 (M+1, 2%), 361 (M+1-THP-HOBn, 42%), 343 (M+1-THP-HPBn, H2O, 100%); m.p. 52-56° C.; Anal. calcd. for C36H56O4: C=78.21; H=10.21. Found: C=77.93; H=10.39.
