Cl[C:2]1[CH2:6][C:5]([CH3:8])([CH3:7])[CH2:4][C:3]=1[CH:9]=O.C(N(CC)CC)C.[SH:18][CH2:19][C:20]([O:22][CH2:23][CH3:24])=[O:21]>ClCCl>[CH3:8][C:5]1([CH3:7])[CH2:6][C:2]2[S:18][C:19]([C:20]([O:22][CH2:23][CH3:24])=[O:21])=[CH:9][C:3]=2[CH2:4]1To a solution of 131b (33.0 g, crude) in dichloromethane (400 mL) and triethylamine (60 g, 600 mmol) was added ethyl 2-mercaptoacetate (19.2 g, 160 mmol). See FIG. 15. The reaction mixture was heated at reflux for 6 h. It was then concentrated under reduced pressure. The residue was dissolved in ethanol (400 mL) and triethylamine (60 g, 600 mmol). The mixture was heated at reflux for 12 h. It was concentrated again under reduced pressure and the residue was purified by silica-gel column chromatography eluting with 40:1 petroleum ether/ethyl acetate to 131c as a yellow solid (18.0 g, 32%, over two steps). MS-ESI: [M+H]+ 225.3. 1H NMR (500 MHz, DMSO-d6) δ 7.49 (s, 1H), 4.32 (q, J=7.0 Hz, 2H), 2.72 (s, 2H), 2.56 (s, 2H), 1.35 (t, J=7.0 Hz, 3H), 1.22 (s, 6H).
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