Methanol → cis-5-Norbornene-endo-2,3-dicarboxylic acid monomethyl ester

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The starting material (a) was prepared as described in J. Org. Chem. 2000, 65, 6984-6991. cis-5-Norbornene-endo-2,3-dicarboxylic anhydride (8.21 g, 50 mmol) was suspended in a 1:1 mixture of toluene and carbon tetrachloride (250 mL). The mixture was stirred for 10 min. Quinidine (17.84 g, 55 mmol) was added and the flask was degassed and backfilled with nitrogen. The solution was cooled to −55° C. While stirring, methanol (6.08 mL, 150 mmol) was added. The mixture was stirred at −55° C. for 18 h. Upon warming to 25° C., the mixture was concentrated in vacuo to a thick oil. The oil was dissolved in a mixture of ethyl acetate (400 mL) and 1.0 M aqueous hydrochloric acid solution (300 mL). After shaking, the layers were separated and the organic layer was further washed with 1.0 M aqueous hydrochloric acid solution (2×100 mL), saturated aqueous brine solution (100 mL), dried over magnesium sulfate, filtered, and concentrated in vacuo to afford the desired product, (1S,2R,3S,4R)-3-(methoxycarbonyl)bicyclo[2.2.1]hept-5-ene-2-carboxylic acid (9.15 g, 46.6 mmol, 94%), as a clear oil. 1H NMR (400 MHz, DMSO-d6) δ: 1.26 (1H, d, J=8.4 Hz), 1.33 (1H, d, J=8.4 Hz), 3.00 (1H, s), 3.03 (1H, s), 3.21-3.29 (2H, m), 3.45 (3H, s), 6.02-6.04 (1H, m), 6.14-6.16 (1H, m), 11.86 (1H, s).

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