L-Proline 1,1-dimethylethyl ester → (S)-tert-Butyl-1-(2-(7-nitro-2H-benzo[b][1,4]thiazin-4(3H)-yl)-2-oxoethyl)pyrrolidine-2-carboxylate

Participants

Reaction Conditions

Reaction Steps

A solution of 2-chloro-1-(7-nitro-2H-benzo[b][1,4]thiazin-4(3H)-yl)ethanone (1.0 g, 3.67 mmol) in THF (20 mL) was treated with (S)-tert-butyl pyrrolidine-2-carboxylate (0.942 g, 5.50 mmol), followed by saturated sodium bicarbonate (4 mL). The mixture was heated at 55° C. for 3 hours then stirred at room temperature overnight (17 hours). The mixture was diluted with EtOAc (50 mL) and saturated sodium bicarbonate (10 mL) then stirred for 20 minutes. The contents were poured into a separatory funnel, and the organic layer was separated, dried (Na2SO4), filtered, and concentrated to give a dark yellow residue. This residue was subjected to silica gel chromatography using the Biotage purification system (column: Silicycle 40 g; 20:80 EtOAc:hexanes gradient to 60:40 EtOAc:hexanes over 8 column volumes; flow rate: 35 mL/min; collection wavelength: 254 nm). A yellow residue was obtained (1.47 g, 98%). 1H-NMR (CDCl3) δ 8.09 (d, J=2.4 Hz, 1H), 7.91 (dd, J=2.4, 8.7 Hz, 1H), 7.75 (d, J=9.0 Hz, 1H), 4.10 (brs, 2H), 3.74 (brd, J=13.2 Hz, 1H), 3.40 (brd, J=13.5 Hz, 1H), 3.37-3.21 (m, 3H), 3.12-3.04 (m, 1H), 2.61 (brdd, J=8.1, 16.2 Hz, 1H), 2.21-2.07 (m, 1H), 1.95-1.77 (m, 3H), 1.43 (s, 9H); ESI-MS (m/z, %): 408 (MH+, 50), 352 (100).

Provenance & Evidence