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A solution of 4.37 g (19 mmol) methyl 2-chloro-4,4-dimethoxy-3-oxopentanoate (Intermediate 17) and 1.8 g (24 mmol) thiourea in 50 ml EtOH was heated at reflux for 3 h. Solvent was removed and the residue was dissolved in 1:1 acetone-5N HCl and the solution was heated at reflux for 4 h. Acetone was removed and the aqueous residue was neutralized with 50% NaOH and then basified with aqueous Na2CO3. Precipitated solids were filtered, washed with water and dried in vacuum. NMR: 2.4 (s, 3H), 3.7 (s, 3H), 8.0 (s, 2H).

1. temperatureat reflux for 3 h
2. customSolvent was removed
3. dissolutionthe residue was dissolved in 1:1 acetone-5N HCl
4. temperaturethe solution was heated
5. temperatureat reflux for 4 h
6. customAcetone was removed
7. customPrecipitated solids
8. filtrationwere filtered
9. washwashed with water
10. customdried in vacuum