Diethyl Ether → Heptatriaconta-6,9,28,31-tetraen-19-one

Participants

Reaction Steps

To a flame dried 500 mL 2NRB flask, freshly activated Mg turnings (0.144 g, 6 mmol) were added and the flask was equipped with a magnetic stir bar and a reflux condenser. This set-up was degassed, flushed with argon and 10 mL of anhydrous ether was added to the flask via syringe. The bromide 3 (1.65 g, 5 mmol) was dissolved in anhydrous ether (10 mL) and added dropwise via syringe to the flask. An exothermic reaction was noticed (to confirm/accelerate the Grignard reagent formation, 2 mg of iodine was added and immediate decolorization was observed confirming the formation of the Grignard reagent) and the ether started refluxing. After the completion of the addition the reaction mixture was kept at 35° C. for 1 h and then cooled in ice bath. The cyanide 4 (1.38 g, 5 mmol) was dissolved in anhydrous ether (20 mL) and added dropwise to the reaction mixture with stirring. An exothermic reaction was observed and the reaction mixture was stirred overnight at ambient temperature. The reaction was quenched by adding 10 mL of acetone dropwise followed by ice cold water (60 mL). The reaction mixture was treated with aq. H2SO4 (10% by volume, 200 mL) until the solution became homogeneous and the layers were separated. The aq. phase was extracted with ether (2×100 mL). The combined ether layers were dried (Na2SO4) and concentrated to get the crude product which was purified by column (silica gel, 0-10% ether in hexanes) chromatography. The pure product fractions were evaporated to provide the pure ketone 7 as a colorless oil (2 g, 74%). 1H NMR (CDCl3, 400 MHz) δ=5.33-5.21 (m, 8H), 2.69 (t, 4H), 2.30 (t, 4H), 2.05-1.95 (m, 8H), 1.55-1.45 (m, 2H), 1.35-1.15 (m, 18H), 0.82 (t, 3H). 13C NMR (CDCl3) δ=211.90, 130.63, 130.54, 128.47, 128.41, 43.27, 33.04, 32.01, 30.93, 29.89, 29.86, 29.75, 29.74, 27.69, 26.11, 24.35, 23.06, 14.05. MS. Molecular weight calculated for C37H66O, Cal. 526.92. Found 528.02 (M+H+).

Provenance & Evidence