Reaction Steps
TBAF (1.319 mL, 1.319 mmol) was added to a tetrahydrofuran (6 mL) solution of (5S,6S,9R)-6-(3,5-difluorophenyl)-9-(triisopropylsilyloxy)-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridin-5-yl acetate (0.538 g, 1.099 mmol) at room temperature under nitrogen. The reaction was stirred for 1 h. LCMS showed complete conversion. The solvent was removed via vacuum and the crude mixture was partitioned between ethyl acetate and brine. The ethyl acetate layer was separated, dried (sodium sulfate), filtered and concentrated. Flash chromatography using ethyl acetate in hexane from 0 to 50% gave the desired product (0.2786 g, 75%). (Rf ca. 0.86 in 50% ethyl acetate in hexane). HPLC tR=1.88 min, MS(ESI)[M+H+]=334.21, 1H NMR (400 MHz, CHLOROFORM-d) δ ppm 8.38-8.49 (m, 1H) 7.67 (d, J=7.81 Hz, 1H) 7.26 (dd, J=7.81, 4.78 Hz, 1H) 6.60-6.78 (m, 3H) 6.17 (d, J=10.58 Hz, 1H) 5.92 (d, J=3.78 Hz, 1H) 4.89 (m, 1H) 2.80 (m, 1H) 2.28-2.13 (m, 3H) 1.80 (s, 3H) 1.47 (m, 1H); 19F NMR (376 MHz, CHLOROFORM-d) δ ppm −109.62 (s, 2F); 13C NMR (101 MHz, CHLOROFORM-d) δ ppm 168.94 (s, 1C) 162.82 (dd, J=248.16, 13.10 Hz, 1C) 157.96 (s, 1C) 146.98 (t, J=8.86 Hz, 1C) 146.02 (s, 1C) 133.16 (s, 1C) 132.08 (s, 1C) 122.64 (s, 1C) 110.44 (d, J=25.43 Hz, 1C) 102.14 (t, J=24.66 Hz, 1C) 72.81 (s, 1C) 71.11 (s, 1C) 49.61 (s, 1C) 35.39 (s, 1C) 33.94 (s, 1C) 20.27 (s, 1C). 3. NaHMDS (1.839 mL, 1.839 mmol) was added to a dimethylformamide (4 mL) solution of (5S,6S,9R)-6-(3,5-difluorophenyl)-9-hydroxy-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridin-5-yl acetate (0.2786 g, 0.836 mmol) and 4-nitrophenyl 4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin-1-yl)piperidine-1-carboxylate (0.3337 g, 0.870 mmol) at −20° C. under nitrogen. The reaction was stirred at −20° C. for 3 h, and then treated with 0.1 eq of 4-nitrophenyl 4-(2-oxo-2,3-dihydro-1H-imidazo[4,5-b]pyridin-1-yl)piperidine-1-carboxylate and 0.15 mL of NaHMDS. The reaction was stirred for another hour while it was warmed up to −10° C. LCMS showed the desired product as well as the hydrolyzed alcohol (loss of acetyl group). The reaction was quenched with water, followed by addition of ethyl acetate. The ethyl acetate layer was washed three times by water before separated, dried (sodium sulfate), filtered and concentrated to give the crude product. HPLC tR=2.58 min,
