General procedure for the synthesis of 4-vinylbenzocyclobutene from 4-formylbenzocyclobutene: Triphenylmethylphosphonium bromide ((Ph)3PCH3Br, 24.3 g, 68.1 mmol) and 110 mL of anhydrous tetrahydrofuran (THF) were added to a 500 mL round-bottomed flask, and the solution was cooled to -78 °C. Dropwise n-butyllithium (n-BuLi, 2.5 M hexane solution, 26.4 mL, 66 mmol) was added, and then the reaction mixture was slowly warmed to room temperature. The resulting yellow-orange solution was cooled again to -78 °C and 4-formylbenzocyclobutene (7.16 g, 54.2 mmol) dissolved in 34 mL of anhydrous THF was slowly added. The mixture was warmed to room temperature and stirring was continued for 2 hours. Upon completion of the reaction, the reaction mixture was treated sequentially with saturated ammonium chloride (NH4Cl) solution and saturated sodium bicarbonate (NaHCO3) solution, and the crude product was obtained by filtration through diatomaceous earth, washed with a solvent mixture of ethyl ether/hexane (1:1), and then evaporated to dryness at room temperature. The crude product was further purified by column chromatography using 5% diethyl ether/hexane as eluent followed by Kugelrohr distillation (75 °C, 1.0 mmHg) to afford pure 4-vinylbenzocyclobutene (5.50 g, 78% yield) as a colorless liquid. The product was identified by infrared spectroscopy (IR), with the main absorption peaks located at 2925, 1627, 1473, 989, 901 and 829 cm-1 ; 1H NMR (400 MHz, CDCl3) δ 7.26 (d, 1H, J = 7.4 Hz, ArH), 7.20 (s, 1H, ArH), 7.04 (d, 1H, J = 7.4 Hz. ArH), 6.74 (dd, 1H, J = 17.5 Hz, J = 10.8 Hz, CH), 5.70 (d, 1H, J = 17.5 Hz, CH2), 5.20 (d, 1H, J = 10.8 Hz, CH2), 3.19 (s, 4H, CH2); 13C NMR (100 MHz, CDCl3) δ 146.09, 145.75, 137.94, 136.69, 125.71, 122.58, 119.90, 112.38, 29.52, and 29.35. Elemental analysis (C10H10) Calculated values: C, 92.2%; H, 7.80%. Measured values: C, 92.0%; H, 8.03%.
