[CH2:1]([CH:8]([C:12](O)=O)[C:9]([OH:11])=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.C=O.C(NCC)C.Cl>C(OCC)(=O)C.O>[CH2:12]=[C:8]([CH2:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1)[C:9]([OH:11])=[O:10]
A solution of benzylmalonic acid (20.0 g, 0.103 mol, 1 eq) and paraformaldehyde (4.94 g, 0.164 mol, 1.6 eq) in ethyl acetate (150 mL) was cooled (0° C.) and treated with diethylamine (10.65 mL, 0.103 mol, 1 eq) drop wise, keeping the reaction temperature below 20° C. (see FIG. 6). The reaction was then warmed to reflux for 90 min and cooled again on ice. The homogeneous solution was treated with water (20 mL) and concentrated aqueous HCl (12N) (9.0 mL, 0.108 mol) drop wise, keeping the reaction temperature below 10° C. The phases were then separated. The organic layer was washed with brine (100 mL), dried over sodium sulfate, filtered, and the filtrate concentrated under vacuum giving compound 17 as a white solid (15 g, 90%). Rf 0.46 (hexane/EtOAc=7:3). 1H NMR (300 MHz, CDCl3) δ 7.28 (m, 5H), 6.42 (s, 1H), 5.62 (s, 1H), 3.67 (s, 2H). [M−H]− 161.0: tR=2.53 min; purity: 99%.
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