| 42% |
Stage #1: With triethylamine In tetrahydrofuran; water at 30℃; for 0.00861111 h; Flow reactor
Stage #2: at 90℃; for 0.0333333 h; Flow reactor |
In contrast to the other examples, only the cyclisation reaction was performed in flow. TheVapourtec R-series was equipped with three pumps. MSH 1 (2 g, 71 percent damp solid, 6.60 mmol)1 and 3-bromopyridine 2a (1.04 g, 6.60 mmol) were dissolved together in THF/H2O (1:1, 33 mL, 0.2 M). Triethylamine (0.92mL, 6.60 mmol) dissolved in THF (8.25 mL, 0.8 M) was mixed with the first inlet via a Y-piece with flow rates of2.86 mL/min and 1.07 mL/min respectively (1.5 eq of triethylamine). Methyl propiolate 4a (0.56 g, 6.60 mmol) wasdissolved in THF (8.25 mL, 0.8 M) and introduced in a second Y-piece at flow rate 1.07 mL/min (1.5 eq of methylpropiolate). The system solvent was THF. The PFA reactor coils, with volumes 2 mL and 10 mL respectively, were setto temperatures 30 °C and 90 °C respectively. The reaction mixture from the first two inlet streams spent 31 secondsresidency time in the first reactor and then 2 minutes residency time in the second reactor. The operating pressure was7.5 bar with 3 pumps. The reaction set-up was flushed afterwards with 33 percent HCl (conc.) in MeOH followed by IPA.The total flow rate at the outlet was 5 mL/min. The outlet stream (40 mL, collected over 8 minutes) was concentratedin vacuo to remove the THF and then diluted with EtOAc (250 mL) and brine (100 mL). The organic layer wasseparated and the aqueous phase washed twice more with EtOAc (2 x 200 mL). The combined organic layers weredried over anhydrous sodium sulfate and concentrated in vacuo to give a dark red oil.The crude material was purified by column chromatography on a 100 g silica column using the Biotage machine anda gradient from 7 to 60 percent EtOAc/heptane. 5a eluted first from the column. Pale red solid (0.43 g, 8 min collectiontime, 42 percent). 1H NMR (400 MHz, d6-DMSO) 4.10 (3H, s, CH3), 7.79 (1H, d, J = 8 Hz, ArH), 8.26 (1H, d, J = 8 Hz,ArH), 8.73 (1H, s, ArH), 9.56 (1H, s, ArH) ppm. 13C NMR (101 MHz, d6-DMSO) 51.2, 103.3, 108.1, 118.8, 130.3,131.4, 138.7, 144.6, 162.6 ppm. HRMS (FAB) calcd for C9H8O2N2Br 254.97637, found 254.97636/256.97421.5b eluted second from the column. Pale yellow solid. (0.14 g, 8 min collection time, 14 percent). 1H NMR (400 MHz, d6-DMSO) 3.82 (3H, s, CH3), 7.06 (1H, dd, J = 4 and 4 Hz, ArH), 7.87 (1H, d, J = 4 Hz, ArH), 8.50 (1H, s, ArH), 8.93(1H, d, J = 4 Hz, ArH) ppm. 13C NMR (101 MHz, d6-DMSO) 51.3, 104.7, 109.8, 114.4, 129.8, 132.8, 137.6, 145.6,161.9 ppm. HRMS (FAB) calcd for C9H8O2N2Br 254.97637, found 254.97638/256.97424 |
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