[CH3:1][O:2][C:3]1[CH:4]=[C:5]2[C:9](=[CH:10][CH:11]=1)[NH:8][C:7]([C:12]([O:14][CH3:15])=[O:13])=[CH:6]2.[CH3:16][S:17]([CH3:19])=O.[ClH:20]>CO>[Cl-:20].[CH3:1][O:2][C:3]1[CH:4]=[C:5]2[C:9](=[CH:10][CH:11]=1)[NH:8][C:7]([C:12]([O:14][CH3:15])=[O:13])=[C:6]2[S+:17]([CH3:19])[CH3:16]A mixture of methyl 5-methoxy-1H-indole-2-carboxylate (8.3 g, 40 mmol; Blaikie KG, Perkin WH Jr, J. Chem. Soc. 1924;125:296) and dimethyl sulfoxide (4.0 mL, 4.4 g, 56 mmol) in 75 mL of methanol is cooled in ice and treated with gaseous HCl. The temperature of the reaction mixture increases to 45° C. as the HCl is added. Additional HCl is added intermittently and the rate of cooling is adjusted so that a reaction temperature of 40°-50° C. is maintained for 3 hours. The mixture is cooled and the precipitated solid filtered and washed with ether to yield 6.3 g (52%) of [5-methoxy-2-(methoxycarbonyl)-1H-indol-3-yl] dimethylsulfonium chloride suitable for further synthesis; mp 130° C.-dec.
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