[CH3:1][O:2][C:3]([C:5]1([C:10]([O:12]C)=[O:11])[C:7]2([CH2:9][CH2:8]2)[CH2:6]1)=[O:4].[OH-].[K+].Cl>CO.O>[CH3:1][O:2][C:3]([C:5]1([C:10]([OH:12])=[O:11])[C:7]2([CH2:9][CH2:8]2)[CH2:6]1)=[O:4]To the mixture of spiro[2.2]pentane-1,1-dicarboxylic acid dimethyl ester 800 mg (4.3 mmol) in 8 mL of MeOH and 2 mL of water was added KOH (240 mg, 4.3 mmol). This solution was stirred at rt for 2 days. It was then acidified with dilute HCl to pH 3 and extracted two times with ether. The combined organic phases were dried (MgSO4) and concentrated to yield 600 mg (82%) of spiro[2.2]pentane-1,1-dicarboxylic acid methyl ester as a white solid. 1H NMR (300 MHz, CDCl3) δ 3.82 (s, 6 H), 2.35 (d, 1 H, J=3 Hz), 2.26 (d, 1 H, J=3 Hz), 1.20 (m, 1 H), 1.15 (m, 1 H), 1.11 (m, 1 H), 1.05 (m, 1 H). LRMS: MS m/z 169 (M+−1).
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