Hydrochloric Acid → 6-(3,4-Dimethoxy-benzoyl)-cyclohex-3-enecarboxylic acid

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A solution of 17 (59 mmol, 0.29 M) in THF was added dropwise to an ice-cooled solution of cis-1,2,3,6-tetrahydrophthalic anhydride in THF (120 mL) over a 1 hr period. After the addition was complete, the resulting mixture was stirred for another 30 min at 0° C. The reaction mixture was allowed to warm to rt and stirred overnight. The reaction was then stopped with sat. NH4Cl and the pH adjusted to 2 with concentrated HCl(aq) and then extracted with diethyl ether. The organic layer was washed with water and subsequently extracted with 1 M NaOH. The combined aqueous extract was acidified with concentrated HCl and extracted with EtOAc (3×100 mL). The organic layers were combined and dried over MgSO4, filtered, and concentrated under reduced pressure to afford oil. The oil was dissolved CH2Cl2 and filtered through silica gel to remove the dicarboxylic acid formed during workup. The product was recrystallized from diethyl ether to afford pure product (1.62 g, 10%) as a white solid; mp=109° C.; LRMS ESI [m−H]− cacld for C16H18O5 289, found m/z 289; 1H NMR (CDCl3, 500 MHz): δ 7.60-7.53 (m, 2 H), 6.92 (d, J=8.4 Hz, 1 H), 5.84-5.82 (m, 1 H), 5.71-5.68 (m, 1 H), 4.03-4.00 (m, 1 H), 3.98 (s, 3 H), 3.95 (s, 1 H), 3.10-3.07 (m, 1 H), 2.90-2.84 (m, 1 H), 2.54-2.44 (m, 3 H).

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