Lithium Chloride → {2-Ethyl-4-[6-methoxy-7-methyl-3-oxo-4-(2-trimethylsilanyl-ethoxy)-1,3-dihydro-isobenzofuran-5-yl]-but-2-enyloxymethyl}-phosphonic Acid Diisopropyl Ester

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To a solution of bromomethylphosphonate diisopropyl ester (680 mg, 2.62 mmol) and 6-(3-hydroxymethyl-pent-2-enyl)-5-methoxy-4-methyl-7-(2-trimethylsilanyl-ethoxy)-3H-isobenzofuran-1-one (688 mg, 1.75 mmol) in DMF (3 mL) was added lithium t-butoxide (1.0M in THF; 2.6 mL). The reaction was heated at 70° C. for 2 hours. After cooling to ambient temperature, more bromomethylphosphonate diisopropyl ester (680 mg, 2.62 mmol) and lithium t-butoxide (1.0M in THF; 2.6 mL) were added. The reaction mixture was heated at 70° C. for a further hour, cooled, poured into a solution of lithium chloride (5% aqueous) and extracted with ethyl acetate. The organic extract was dried and the product was purified by chromatography on silica gel, eluting with hexane-ethyl acetate to provide 347 mg (35%) of the product as a colorless oil. 1H NMR (300 MHz, CDCl3) δ 0.04 (s, 9H), 1.09 (t, 3H, J=7.5 Hz), 1.20-1.26 (m, 2H), 1.31 (t, 12H, J=6 Hz), 2.18 (s, 3H), 2.29 (q, 2H, J=7.5 Hz), 3.5 (m, 2H), 3.59 (d, 2H, J=8.7 Hz), 3.78 (s, 3H), 3.98 (s, 2H), 4.28-4.35 (m, 2H), 4.6-4.8 (m, 2H), 5.13 (s, 2H), 5.4 (t, 1H, J=7 Hz) ppm; 31P (121.4 MHz, CDCl3) δ 20.26 ppm; MS (m/z) 593.3 [M+Na]+.

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