n-Butyl lithium (1.6 M in hexanes, 1 mL) was added to an equal volume of THF at −20° C. A solution of diethyl methylphosphonate (220 mg, 1.45 mmol) in THF (1 mL) was then added dropwise and the solution was stirred for 30 minutes. After cooling at −60° C., the solution was transferred via a cannula to a vial containing copper(I) iodide (276 mg, 1.45 mmol), and the resulting mixture was stirred for 1 h at −30° C. A solution of 6-(4-bromo-3-methyl-but-2-enyl)-7-hydroxy-5-methoxy-4-methyl-3H-isobenzofuran-1-one 158B (50 mg, 0.15 mmol) in THF (1 mL) was added and the mixture was allowed to warm to 0° C. for 2 h before saturated aqueous ammonium chloride was added. The reaction mixture was acidified with 2 N HCl and extracted with ethyl acetate. The ethyl acetate extract was concentrated and the residue was chromatographed on silica gel (40% to 100% ethyl acetate/hexanes), affording [5-(4-hydroxy-6-methoxy-7-methyl-3-oxo-1,3-dihydro-isobenzofuran-5-yl)-3-methyl-pent-3-enyl]-phosphonic acid diethyl ester 158C as an oil (27 mg, contaminated with the starting diethyl methylphosphonate); 1H NMR (300 MHz, CDCl3) δ 1.32 (m, 6H), 1.8-1.9 (m, 5H), 2.18 (s, 3H), 2.25 (m, 2H), 3.42 (d, J=7.2 Hz, 2H), 3.78 (s, 3H), 4.15 (m, 4H), 5.21 (s, 2H), 5.24 (t, J=7.2 Hz, 1H), 7.65 (s, 1H) ppm.
