Acetic acid, phosphono-, 1-(1,1-dimethylethyl) ester, diammonium salt → HCID 67313493, compound

To a stirred solution of tert-butyl phosphonoacetate (1.7 g, 7.27 mmol) in THF (20 mL) was slowly added n-butyllithium (1.6 M, 5 mL) with cooling to −78 degrees Celsius. After stirring for 30 minutes at −78 degrees Celsius, this solution was added into a solution of 6-formyl-benzo[b]thiophene-2-carboxylic acid ethyl ester (1.83 g, 7.27 mmol). The resulting solution was stirred at −78 degrees Celsius for 30 minutes before being allowed to warm to room temperature. The solution was subsequently cooled back to −78 degrees Celsius and quenched with sat. aq NH4Cl. The mixture was extracted with ethyl acetate, and the combined organic extracts were dried over anhydrous sodium sulfate. After being filtrated and concentrated, the residue was purified by flash column chromatography to give 1.7 g (71%) of 6-(2-tert-butoxycarbonyl-vinyl)-benzo[b]thiophene-2-carboxylic acid ethyl ester. MS: calc'd 333 (MH+), exp 333 (MH+). 1H NMR (d6-DMSO, 400 MHz), 8.38 (s, 1H), 8.18 (s, 1H), 8.02 (d, 1H, J=8.4 Hz), 7.82 (d, 1H, J=8.4 Hz), 7.66 (d, 1H, J=16.0 Hz), 6.66 (d, 1H, J=16.0 Hz), 4.36 (q, 2H, J=7.2 Hz), 1.49 (s, 9H), 1.34 (t, 3H, J=7.2 Hz).