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, 1M 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.
