Diisopropylamine → Lithium diisopropylamide

Participants

Reaction Steps

A solution of lithium diisopropylamide in anhydrous THF was prepared by addition of n-butyllithium (7.9 ml of a 1.6M solution in hexane, 12.64 mmol) to a solution of diisopropylamine (1.4 g, 13.9 mmol) in THF (200 ml), at -78° C. The solution was stirred for 0.5 h before adding dropwise to a stirred solution of 1-methyl-3-carbomethoxypyrrolidine (1.5 g, 10.5 mmol) in THF (200 ml), at -78° C. After 1 h, a solution of 2-iodopyrazine (2.73 g, 13.3 mmol) in THF (10 ml) was added dropwise, at -78° C., stirred for 0.25 h, warmed to room temperature, and stirred for a further 16 h. Water (25 ml) and dichloromethane (150 ml) were added, stirred for 0.25 h before separating the aqueous and extracting into dichloromethane (3×100 ml). The combined extracts were dried (Na2SO4), concentrated under vacuum, and the residue purified by silica-gel chromatography using dichloromethane/methanol (92:8) as eluant. The title pyrazine was obtained as an orange oil (0.36 g) m/e 222 (M+); δ(360 MHz, CDCl3) 2.38 (3H, s, N--Me); 2.43-2.51 (1H, m, CH of CH2); 2.66-2.92 (3H, m, CH of CH2 and CH2 --N); 3.15 (1H, d, J=9.7 Hz, CH of CH2 --N) 3.33 (1H, d, J=9.7 Hz, CH of CH2 --N); 3.72 (3H, s, CO2Me); 8.44 (1H, d, J=1.5 Hz, pyrazine-H); 8.49 (1H, d, J=2 Hz, pyrazine-H), 8.64 (1H, dd, J=1.5 and 2 Hz, pyrazine-H).

Provenance & Evidence