5,5-Diethoxy-1,1,1-trifluoro-pent-3-yn-2-one (2 g, 8.9 mmol) and 2-hexyl-isothiourea hydrobromide (2.4 g, 9.8 mmol) were dissolved under nitrogen in THF (20 mL). Then triethylamine (2.7 mL, 19.6 mmol) was added slowly. The reaction was exothermic (40° C.). The suspension was stirred for 4 h at 20° C. The product was extracted with AcOEt, sat. NH4Cl solution, dried and concentrated. The residue was purified by silica gel chromatography in heptane/AcOEt 20:1. One obtained 2.5 g (76%) of a colorless oil. MS: m/z=367 (M+H).
