(6bR*,9aR*)-6-(2-Benzyloxy-1-oxoethyl)-6b,9a-dihydro-5-hydroxy- 4-methoxyfuro[3,2-b]naphtho[2,1-d]furan-8(9H)-one

A solution of ceric ammonium nitrate (37 mg, 0.067 mmol) in water was added dropwise to a vigorously stirred solution of naphthol 1 (13 mg, 0.036 mmol) [1] in acetonitrile (2.2 mL) at room temperature and stirred for 15 min. Anhydrous magnesium sulfate was added and the resultant suspension immediately cooled to 0°C. After 1min., a solution of 2-trimethylsilyloxyfuran 2 (0.012 mL, 0.071 mmol) in acetonitrile (0.2 mL) was added dropwise and the resultant solution stirred at 0°C for 30 min. The reaction mixture was diluted with dichloromethane (5 mL), washed with water (2 × 3 mL) and dried over magnesium sulfate. The solvent was removed under reduced pressure to give an orange oil, which was then purified by flash chromatography using light petroleum-ethyl acetate (4:1) as eluent to afford the title compound 3 (9 mg, 60%) as a yellow oil.

IR (cm⁻¹, neat): 3320w, 1785s, 1731, 1077.

¹H NMR (200 MHz, CDCl₃): 3.10–3.12 (2H, m, H9), 4.12 (3H, s, OMe), 4.67 (1H, d, J_gem 12.0 Hz, OCH^APh), 4.77 (1H, d, J_gem 18.1 Hz, COCH^A), 4.88 (1H, d, J_gem 12.0 Hz, OCH^BPh), 4.95 (1H, d, J_gem 18.1 Hz, COCH^B), 5.43–5.49 (1H, m, H9a), 6.80 (1H, d, J_6b,9a 6.1 Hz, H6b), 6.98 (1H, J_3,2 7.0 and J_3,1 2.0 Hz, H3), 7.28–7.60 (7H, m, H1, H2, Ph), 10.46 (1H, s, OH).

EI-MS: 420 (M⁺, 2%), 299 (M-CH₂OBn, 25), 269 (M-C₉H₁₁O₂, 13), 149 (COCH₂OBn, 15), 91 (C₇H₇, 100), 57 (CH₃CH₂CO, 67), 43 (CH₃CO, 54).

Anal. calc. for C₂₄H₂₀O₇ MH⁺ (CI, NH₃), 421.1286; found MH⁺, 421.1287.