The synthesis of BDADPE was carried out by the classical Wittig reaction under argon atmosphere using 4,4'-bis(dimethylamino)benzophenone as substrate (for details, refer to the method of Hirao [29]). The procedure was as follows: methyltriphenylphosphonium bromide (45.58 g, 127.6 mmol) was added to a round-bottomed flask equipped with a reflux condenser and a magnetic stirrer with freshly distilled tetrahydrofuran (THF, 500 mL). Subsequently, potassium tert-butoxide (138.4 mL of a 1.0 M THF solution, 138.4 mmol) was slowly added dropwise to the reaction flask through a constant pressure dropping funnel. The reaction mixture was stirred at 0 °C for 2 hours. Next, a solution of anhydrous THF (690 mL) of 4,4'-bis(dimethylamino)benzophenone (21.4 g, 79.75 mmol) was added dropwise to the reaction mixture at 0 °C via a constant pressure dropping funnel. The orange-brown reaction mixture was heated and refluxed with stirring for 7 h. The reaction was quenched with distilled water upon completion. The resulting mixture was extracted three times with ether. The combined ether layers were washed sequentially with aqueous NaHCO3 and saturated aqueous NaCl and then dried with anhydrous MgSO4. After filtration, the ether layer was poured into hexane to precipitate triphenylphosphine oxide. Purification by fast column chromatography (eluent: petroleum ether/ethyl acetate, 2:1 v/v) afforded BDADPE in 92% yield (19.52 g, 73.37 mmol) with an Rf-value of 0.76. The structure of the product was confirmed by 1H NMR (CDCl3, 400 MHz): δ 2.96 (s, 12H, 2×N(CH3)2), 5.19 (s , 2H, CH2=C), 6.68-6.70 (d, 4H, aromatic proton neighbor of N(CH3)2), 7.25-7.28 (d, 4H, aromatic proton with N(CH3)2).
