Cl[C:2]([O:4][CH3:5])=[O:3].[NH2:6][C:7]1[S:8][CH2:9][C:10](=O)[C:11]=1[C:12]#[N:13].[CH2:15](N(CC)CC)C.Cl>ClCCl.ClCCl.CO>[C:12]([C:11]1[C:10]([CH3:15])=[CH:9][S:8][C:7]=1[NH:6][C:2](=[O:3])[O:4][CH3:5])#[N:13]
Methyl chloroformate (55 g, 0.58 mol) was added to a stirred solution of 2-amino-4-oxo-4,5-dihydrothiophene-3-carbonitrile (68 g, 0.49 mol) and triethylamine (147 g, 1.45 mol) in dichloromethane (1000 ml) at 0° C. After the addition, the mixture was warmed to 25° C. and stirred overnight. The reaction was treated with dichloromethane-methanol (20:1, 2000 mL) and 2N hydrochloric acid (1500 mL). The resulting mixture was filtered and the resulting solid was further extracted with dichloromethane-methanol (20:1, 1500 mL×3). The combined organic extracts were dried over sodium sulfate and concentrated to give a brown solid. The solid was washed with tert-butyl methyl ether (1500 mL) and dried under vacuum to give crude methyl 3-cyano-4-methylthiophen-2-ylcarbamate (160 g) as a brown solid, which was used in next step without purification.
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