C([O:3][C:4]([C:6]1[S:7][CH:8]=[C:9]2[CH2:14][C:13]([CH2:17][CH3:18])([CH2:15][CH3:16])[CH2:12][CH2:11][C:10]=12)=[O:5])C>CCO.[Li+].[OH-].[OH-].[Na+]>[CH2:17]([C:13]1([CH2:15][CH3:16])[CH2:12][CH2:11][C:10]2=[C:6]([C:4]([OH:5])=[O:3])[S:7][CH:8]=[C:9]2[CH2:14]1)[CH3:18]A solution of 5,5-diethyl-4,5,6,7-tetrahydro-benzo[c]thiophene-1-carboxylic acid ethyl ester (14.2 g, 53.38 mmol) in EtOH (250 mL) and 2 N aq. LiOH (250 mL) is stirred at 65° C. for 18 h. The mixture is diluted with 1 N aq. NaOH and extracted with Et2O. The aq. phase is acidified to pH 2 with 2 N aq. HCl and extracted with DCM. The combined DCM extracts are dried over Na2SO4, filtered, and the solvent is removed in vacuo. The crude product (11.3 g) is purified by MPLC on RP-C18 silica gel to give 5,5-diethyl-4,5,6,7-tetrahydro-benzo[c]thiophene-1-carboxylic acid (2.93 g) as a brown oil; LC-MS: tR=1.01 min, [M+1+CH3CN]=280.19; 1H NMR (CDCl3): δ 7.12 (s, 1H), 2.99 (t, J=7.0 Hz, 2H), 2.46 (s, 2H), 1.59 (t, J=7.0 Hz, 2H), 1.40-1.20 (m, 4H), 0.84-0.74 (m, 6H).
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