92% |
|
Part A: Tert-butyl 3-(trifluoromethylsulfonyloxy)-8-azabicyclo[3.2.1]oct-3-ene-8-carboxylate To a solution of tert-butyl 3-oxo-8-azabicyclo[3.2.1 ]octane-8-carboxylate (450 mg, 2.0 mmol) in THF (15 ml) at -78 C. was added lithium bis(trimethylsilyl)amide (1 M in THF, 2.2 ml, 2.2 mmol) and the reaction solution was stirred for 1 h. A solution of N-(5-chloropyridin-2-yl)-1,1,1-trifluoro-N-(trifluoromethylsulfonyl)methanesulfonamide (864 mg, 2.2 mmol) in THF (20 ml) was added drop wise. The reaction mixture was stirred for another 0.5 h and allowed to warm to room temperature over 3 h and quenched with saturated sodium bicarbonate. The reaction mixture was diluted with ethyl acetate and washed with 15% potassium hydrogen sulfate, saturated sodium bicarbonate solution, 1 N sodium hydroxide, water and brine. The combined organic layers were dried over magnesium sulfate and concentrated in vacuo. Flash chromatography (silica gel, 10% ethyl acetate/hexane) gave the product as a colorless oil (659 mg, 92% yield) 1H NMR (400 MHz, CHLOROFORM-D) delta ppm 6.08 (s, 1H), 4.32-4.58 (m, 2H), 2.90-3.15 (m, 1H), 2.23 (br. s, 1H), 1.98-2.07 (m, 3H), 1.67-1.78 (m, 1H), 1.57 (s, 1H), 1.45 (s, 9H). |
80% |
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3.2 3-Trifluorosulfonyl-8-tert-butyloxycarbonyl-8-azabicyclo[3.2.1]-oct-2-ene (N-Boc-nortropanone enol triflate) (104KS22). LDA was generated by adding BuLi (20 mL, 1.68M, 32.6 mmol) to a solution of diisopropylamine (2.38 g, 32.6 mmol) in dry THF (10 mL) at -78 C. under argon. The mixture was kept at that temperature for 30 min followed by the addition of a solution of N-Bocnortropinone (5.27 g, 23.4 mmol) in dry THF (20 mL). The mixture was then left stirring for 1 h while maintaining the temperature at 78 C. Then a solution of 2-[N,N-Bis(trifluoromethylsulfonyl)amino]-5-chloropyridine (10.08 g, 25.7 mmol) in dry THF (20 mL) and the mixture was slowly allowed to reach room temperature overnight and subsequently concentrated and exposed to column chromatography (SiO2; EtOAc/heptane 1:6, Rf(product)=0.31) to give the title compound (104KS22) (6.68 g, 80%) which on prolonged standing crystallized into a white solid. 1H NMR (CDCl3) delta 1.43 (s, 9H, Boc-C3), 1.72 (m, 1H), 1.93-2.03 (m, 2H), 2.07 (d, J=16.6 Hz, 1H), 2.23 (broad m, 1H), 3.05 (broad s, 1H), 4.42 (broad m, 2H, H1+H5), 6.10 (broad s, 1H, H2). 13C NMR (CDCl3) delta 28.4 (Boc H3), 30.1 and 29.2 (rotameric), 34.7 and 34.9 (rotameric), 36.5 and 37.1 (rotameric), 51.9, (broad s), 80.5 ((CH3)3-), 118.7 (-F3, q, J=300 Hz), 124.0 (broad s, C2), 148.0 (broad s, C3), 153.9 (Boc C=O). |