[CH:1]1[CH:6]=[C:5]([Cl:7])[C:4]([Cl:8])=[C:3]([C:9]2[N:14]=[N:13][C:12]([NH2:15])=[N:11][C:10]=2[NH2:16])[CH:2]=1.ClC1C(Cl)=CC=CC=1C(C#N)=O.ClC1C(Cl)=CC=CC=1C(OC(=O)C1C=CC=C(Cl)C=1Cl)=O.C(=O)(O)O.NNC(N)=N>S(=O)(=O)(O)O>[Cl:8][C:4]1[C:5]([Cl:7])=[CH:6][CH:1]=[CH:2][C:3]=1/[C:9](=[N:14]/[NH:13][C:12]([NH2:15])=[NH:11])/[C:10]#[N:16]
The synthesis of lamotrigine is illustrated in Reference Example 1. 2,3-Dichlorobenzoyl cyanide, which is intermediate 1.4 in that synthesis, may contain up to 10% of 2,3-dichlorobenzoic anhydride as a contaminant. When the 2,3-dichlorobenzoyl cyanide is treated with a solution of aminoguanidine bicarbonate in sulphuric acid, which is step (d) in Reference Example 1, the adduct (Z)-2-(2,3-dichlorophenyl)-2-(guanidinoimino)acetonitrile (intermediate 1.5) is produced. The anhydride contaminant can then react with the latter adduct to form (Z)-2-(2,3-dichlorophenyl)-2-[N′-(2,3-dichlorobenzoyl)guanidinoimino]acetonitrile, which is the direct precursor to compound B. Cyclisation of the precursor in propan-1-ol under reflux yields compound B.
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