Reaction Steps
Oxygen was bubbled through a solution of the β-benzoate 3a (350 mg, 1.36 mmol) and DBPO (4.3 mg, 0.018 mmol) in benezene-n-heptane (20 mL, 1:1) for 10 h with simultaneous addition of a solution of PhSH (50 mg, 0.45 mmol) in heptane (10 mL) (syringe pump). After completion of the thiol addition, the mixture was kept under oxygen for an addition 15 h, diluted with CH2Cl2 (10 mL), cooled to 4° C. and Ph3P (118 mg, 0.45 mmol) was added in 4 portions. The mixture was stirred at 4° C. for 1 h and at rt for an additional 1 h, the solvents were evaporated, and flash chromatography (hexane-EtOA, 3:1) afforded a mixture (42 mg, 22.3% yield) of (1R,4S,5S,7S,8S)-7-benzoyloxy-4,8-dimethyl-4-phenylthiomethyl-2,3-dioxabicyclo[3.3.1]nonan-8-ol 4a (less polar isomer) and (1R,4R,5S,7S,8S)-7-benzoyloxy-4,8-dimethyl-4-phenylthiomethyl-2,3-dioxabicyclo[3.3.1]nonan-8-ol 4b (more polar isomer, (4a/4b ca. 50:50), Rf 0.26 (EtOAc-hexane, 1:3), colorless semisolid. IR (neat): 3547, 1713, 1271, 711 cm-1. Additional flash chromatography afforded a sample of crystalline 4a (less polar isomer), mp 139-140° C. 1H NMR (400 MHz, CDCl3, δ): 1.37 (br. s, 3 H, Me11), 1.44 (s, 3 H, Me10), 1.83 (ddd, 1 H, 2J=13.1 Hz, 3J6a7a =11.6 Hz, 3J6a5e =3.3 Hz, Ha6), 2.08 (m, 2 H, Ha9 +He9), 2.20 (m, 1 H, He5), 2.37 (m, 1 H, He6), 3.35 (d, 1 H, 2J=12.9 Hz, H12), 3.73 (br. d, 1 H, 2J=12.9 Hz, H'12), 3.96 (dd, 1 H, 3J1e9e =3J1e9a =2.4 Hz, He1), 5.76 (dd, 1 H, 3J7a6a =11.6 Hz, 3J7a6e =6.3 Hz, Ha7), 7.20 (m, 1 H, H16), 7.30 (m, 2 H, H15,15 '), 7.42 (m, 2 H, H14,14 '), 7.48 (m, 2 H, Hmeta-benz.), 7.60 (m, 1 H, Hpara-benz.), 8.03 (m, 1 H, Hortho-benz.). 13C NMR (100 MHz, CDCl3,δ): 22.30 (Me11), 23.68 (C9H2), 24.46 (Me10), 29.23 (C6H2), 31.31 (C5H), 40.54 (C12H2), 72.81 (C8), 74.75 (C6H), 82.75 (C1H), 83.79 (C4), 126.43 (C16H), 128.54 (2CH), 129.03 (2CH), 129.48 (2CH), 129.94 (2CH), 130.07 (C1-benz.), 133.24 (Cp-benz.H), 136.56 (C13), 165.59 (C=O). More polar isomer 4b: 1H NMR (400 MHz, CDCl3, δ): 1.43 (s, 3H, Me10), 1.58 (br.s, 3 H, Me11), 1.77 (ddd, 1 H, 2J=12.8 Hz, 3J6a7a =11.2 Hz, 3J6a5e =3.4 Hz, Ha6), 2.07-2.36 (m, 4 H, He5 +He6 +He,a9), 3.03 (d, 1 H, 2J=12.3 Hz, H12), 3.24 (br. d, 1 H, 2J=12.3 Hz, H'12), 3.99 (m, 1 H, He1), 5.78 (dd, 1 H, 3J7a6a =11.2 Hz, 3J7a6e =6.3 Hz, Ha7), 7.21 (m, 1 H, H16), 7.30 (m, 2 H, H15,15'), 7.42 (m, 2 H, H14,14'), 7.48 (m, 2 H, Hmeta-benz.), 7.59 (m, 1 H, Hpara-benz.), 8.03 (m, 1 H, Hortho-benz.), 13C NMR (100 MHz, CDCl3,δ): 21.40 (Me11), 23.80 (C9H2), 24.46 (Me10), 28.99 (C6H2), 32.53 (C5H), 40.70 (C12H2), 72.83 (C8), 74.81 (C7H), 83.23 (C1H), 83.88 (C4), 126.51 (C16H), 128.52 (2CH), 129.03 (2CH), 129.48 (2CH), 129.90 (2CH), 130.08 (C1-benz.), 133.20 (Cp-benz.H), 135.99 (C13), 165.52 (C=O).
