Sodium acetylide (2.4 g, 0.05 mol) was suspended in dry THF (50 ml) under argon and cooled to -78°C. Selenium powder (3.8 g, 0.048 mol) was added and the mixture was allowed to warm to 0°C and was stirred for 1 h. The mixture was cooled to -78°C and MeOH was added dropwise (30 ml). The mixture was stirred for 15 min and was allowed to warm to 0°C and was stirred for another 2.5 h. From this point on all of the operations were performed in the dark. All of the solutions used were kept at 0°C at all times. The mixture was quenched with water (60 ml) and extracted with pentane (5 ×30 ml). The combined organic extracts were washed with water (2 × 30 ml) and dried over Na₂SO₄. The solvents were removed in vacuo without heating. Obtained red solid was immediately used in the following reaction or stored overnight under nitrogen, in the dark at -30°C. Yield 2.4 g (24%).

¹H NMR (400 MHz, 298 K, CD₂Cl₂) δ_H 6.97 (dd, J^HH = 1.1 Hz, CH=CH), 5.65 (dd, 2H, J_HH = 1.1 Hz, C=CH₂).

¹³C NMR (100 MHz, 298 K, CD₂Cl₂) δ_C 120.5 (CH=CH), 108.2 (C=CH₂), (C=CH₂ peak missing)