Reaction Steps
To a solution containing 7 (4.7 g, 12.8 mmol) and DMAP (81 mg, 0.66 mmol) in DCM (100 mL) was added acetic anhydride (2.6 g, 25.5 mmol) at ambient temperature. After 16 h, the reaction mixture was quenched with a MeOH (ca. 3 mL) and washed successively with 10% aq. Na2CO3 (50 mL), dilute HCl (50 mL), and 10% aq. Na2CO3 (50 mL). The organic solution was concentrated in vacuo and filtered through a short column of silica gel (ca. 25 g) [eluant: DCM (200 mL) to 0.5% (v/v) MeOH/DCM (80 mL) to 2% MeOH/DCM (100 mL) to 5% MeOH/DCM (100 mL)]. The product-containing fractions were combined and concentrated to provide 3.28 g (63%) of 8 as a white foam [Note: 94.3 A % by HPLC analysis]. 1H NMR (300 MHz, CDCl3), ˜1:1 mixture of rotomers: δ7.99 (m, 1H), 7.75-6.61 (m, 9H), 5.28 (m, 1H), 5.20 (m, 2H), 4.23 (m, 1H), 3.82 (dt, J=5.4, 13.5 Hz, 1H), 3.60 (app. t, J=13.2 Hz, 1H), 3.50 (d, J=11.7 Hz, 0.5H), 3.31 (d, J=12.9 Hz, 0.5H), 2.87 (dt, J=5.1, 13.5 Hz, 1H), 2.13 (s, 3H), 2.01 (m, 2H) ppm; 13C NMR (75 MHz, CDCl3), ˜1:1 mixture of rotomers: δ170.8, 160.2 (JCF=236.4 Hz), 155.2, 136.8, 136.6, 136.4, 128.9, 128.8, 128.5 (JCF=24.3 Hz), 124.5 (JCF=21.4 Hz), 123.0, 123.0, 120.0 (JCF=27.1 Hz), 119.9 (JCF=26.0 Hz), 112.8 (JCF=10.5 Hz), 108.2 (JCF=24.3 Hz), 97.7 (JCF=25.7 Hz), 74.0, 73.2, 67.9, 67.2, 58.5, 57.6, 53.4, 53.0, 35.4, 34.6, 30.8, 29.7, 21.5 ppm. Mass spectrum (ESI), m/z 410.6 [(M)+; calcd for C23H23FN2O4: 410.4].
