Synthesis
a) Synthesis of ethyl (4-chlorophenyl)-propynoate (Va): Under argon protection, a dry four-necked flask containing 1-chloro-4-iodobenzene (130.0 g, 0.55 mol), bis(triphenylphosphine)palladium(II) chloride (7.57 g, 10.8 mmol, 2 mol%), and cuprous(I) iodide (4.19 g, 22.0 mmol, 4 mol%) was added to a dry four-necked flask was added with anhydrous THF (1.4 L). Cesium carbonate (355.3 g, 1.09 mol, 2 equiv) was added slowly over 5 min at room temperature. Subsequently, ethyl propargylate (111.3 mL, 1.09 mol, 2 eq.) was added and the reaction mixture was stirred at 35 °C overnight. Upon completion of the reaction, ethyl propiolate (11.1 mL, 0.11 mol, 0.2 eq.) was added retrospectively and stirring was continued at 35 °C for 3 hours. The reaction mixture was concentrated to dryness by rotary evaporation and the residue was dissolved in toluene (0.5 L) and heptane (1 L). The resulting suspension was stirred at 40 °C for 1 h and then filtered through diatomaceous earth. The filtrate was concentrated and purified by silica gel column chromatography (eluent: toluene/heptane, 1:2, v/v) to give the light yellow solid product Va (72.6 g, 61% yield).
References
[1] Patent: US2010/152462, 2010, A1. Location in patent: Page/Page column 4
[2] Patent: US2011/144081, 2011, A1. Location in patent: Page/Page column 45-46
[3] Patent: WO2011/85886, 2011, A1. Location in patent: Page/Page column 91-92
[4] Organic Letters, 2013, vol. 15, # 18, p. 4888 - 4891
[5] Organic Letters, 2014, vol. 16, # 10, p. 2606 - 2609
