Abstract: Immunomodulatory imide drugs form the core of many pharmaceutically relevant structures, but Csp2–Csp2 bond formation via metal-catalyzed cross coupling is difficult due to the sensitivity of the glutarimide ring ubiquitous in these structures. We report that replacement of the traditional alkali base with a fluoride source enhances a previously challenging Suzuki–Miyaura coupling on glutarimide-containing compounds with trifluoroborates. These enabling conditions are reactive enough to generate these derivatives in high yields but mild enough to preserve both the glutarimide and its sensitive stereocenter. Experimental and computational data suggest a mechanistically distinct process of π-coordination of the trifluoroborate enabled by these conditions.
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Stage #1: With n-butyllithium In tetrahydrofuran; hexane at -78℃; for 0.5 h; Stage #2: at -78℃; for 0.5 h;
To a stirred solution of 3-bromo-4-methylthiophene (2.7 g, 15.6 mmol) in THF (35 mL) was added n-BuLi (1.6 M in hexane, 14.6 mL, 23.3 mmol) at -78 °C dropwise over a period of 15 min and the mixture was stirred at -78 °C for 30 min. The C02 (gaseous) was passed through the reaction mixture for 10 min and the mixture was stirred at the same temperature for 20 min. Thereafter, the reaction mixture was warmed to 0 °C, quenched with aqueous 1 M NaOH (60 mL) and washed with EtOAc (2 x 50 mL). The aqueous layer was acidified to pH ~ 5 and extracted with DCM (2 x 50 mL). The combined organic layers were washed with water (100 mL), brine (100 mL), dried over anhydrous Na2S04 and concentrated under reduced pressure. The residue was purified by column chromatography (silica gel, 8percent MeOH/DCM as eluent) to provide compound A56-1 (1.5 g^ 70percent) as a white solid
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