abstract |
The present invention relates to a method of producing compound 1, or a salt thereof; comprising precipitating or crystallizing compound 1 from a solution of compound 2, in the presence of a catalyst, wherein the catalyst is 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), acetic acid, trifluoroacetic acid, diisopropylethylamine, or ammonium hydroxide. |