1,3-Bis(pyrrolidin-2-on-1-yl)but-1-ene

To a solution of 1-vinyl-2-pyrrolidinone (1, 11.1 g, 100 mmol) in CH₂Cl₂ (100 ml) was added a drop of CF₃CO₂H at room temperature. The resulting solution was stood at room temperature for 24 h. The solvent was evaporated under reduced pressure. The residue is the desired product 2 (11.1 g, 100%). The product can be recrystallise from acetone.

M.p. 73.2-74.8°C (Lit. [1]: 75°C).

IR(cm^-1, neat): 3070m, 1700vs, 1690vs, 1675vs, 1655vs, 1405vs, 1285vs, 1240s, 955s, 730s.

¹H-NMR(CDCl₃): 7.00 (d, J = 14.2, 1H, H-1), 4.94 (dd, J = 14.2, 6.0, 1H, H-2), 4.89 (m, 1H, H-3), 3.49 (t, J = 7.2, 2H, NCH₂), 3.30 (m, 2H, NCH₂), 2.50 (t, J = 8.1, 2H, COCH₂), 2.40 (t, J = 8.1, 2H, COCH₂), 2.12 (m, 2H, CH₂), 2.00 (m, 2H, CH₂), 1.30 (d, J = 7.0, 3H, Me).

¹³C-NMR(CDCl₃): 174.2 (C, NCO), 173.3 (C, NCO), 125.1 (CH, C-1), 110.7 (CH, C-2), 46.0 (CH, C-3), 45.2 (CH₂, NCH₂), 42.4 (CH₂, NCH₂), 31.4 (CH₂, COCH₂), 31.2 (CH₂, COCH₂), 18.0 (CH₂), 17.4 (CH₃, C-4), 17.0 (CH₂).

EI-MS: 223 (M+H⁺, 6), 222 (M⁺, 36), 207 (M⁺-Me, 37), 204 (27), 179 (13), 138 (36), 124 (34), 122 (21), 112 (43), 110 (29), 109 (32), 98 (26), 96 (20), 94 (24), 82 (41), 81 (100), 80 (24), 70 (27), 69 (55), 56 (23), 55 (35).