Sodium Iodide → ethyl (2E)-4-(diformylamino)but-2-enoate

Prepared according to WO 2010/031816. In a 250 mL RBF, sodium diformylamide (Fluka; 2.66 g, 28.0 mmol) and NaI (3.49 g, 23.31 mmol) were treated with ACN (60 mL) and (E)-ethyl 4-bromobut-2-enoate (Aldrich; 4.28 mL, 23.31 mmol) and the flask was fitted with a reflux condenser and heated at reflux overnight (16 h). The mixture was concentrated in vacuo and the crude residue was treated with water and extracted with EtOAc (100 mL). The organic extract was washed with brine, then dried over MgSO4, filtered, and concentrated. The resulting light-brown solid was suspended in Et2O (ca. 10 mL), filtered, and washed with Et2O (5 mL), then dried by drawing air through the filtercake for 2 min to afford (E)-ethyl 4-(N-formylformamido)but-2-enoate (3.66 g, 19.76 mmol, 85% yield) as a brown amorphous solid: 1H NMR (400 MHz, CDCl3) δ ppm 8.91 (2H, br. s.), 6.74-6.84 (1H, m), 5.90 (1H, dt, J=15.8, 1.6 Hz), 4.40 (2H, d, J=4.5 Hz), 4.13-4.24 (2H, m), 1.20-1.33 (3H, m). m/z (ESI, +ve ion) 186.1 (M+H)+. The crude material was used in the subsequent step without further purification.