N(OC(C)(C)C)=O.N[C:9]1[CH:10]=[C:11]([CH:16]=[C:17]([O:20][CH3:21])[C:18]=1[Cl:19])[C:12]([O:14][CH3:15])=[O:13].[ClH:22].C([O-])(O)=O.[Na+].N>CC#N.[Cu](Cl)Cl>[Cl:22][C:9]1[CH:10]=[C:11]([CH:16]=[C:17]([O:20][CH3:21])[C:18]=1[Cl:19])[C:12]([O:14][CH3:15])=[O:13]
A suspension of copper (II) chloride (0.97 g, 7.2 mmol) and tert-butyl nitrite (1.07 mL, 9.04 mmol) in anhydrous MeCN (5 mL) was warmed to 65° C. A solution of methyl 3-amino-4-chloro-5-methoxybenzoate (4) (1.3 g, 6.0 mmol) in anhydrous MeCN (3 mL) was added dropwise. Once the addition was complete the mixture was allowed to cool to RT and poured on to 1M HCl (15 mL). The acidic mixture was neutralized with satd. NaHCO3 solution and aq. ammonia (35%, 5 mL) was added. The product was extracted with DCM (25 mL) and then washed with aq. ammonia (17.5%, 20 mL) and brine (2×20 mL). The solvent was removed in vacuo and the residue was triturated with 10% EtOAc in isohexane to afford methyl 3,4-dichloro-5-methoxybenzoate (5) (1.17 g, 79% yield) as a brown solid: 1H NMR (400 MHz, DMSO-d6) δ: 7.72 (1H, d), 7.57 (1H, d), 3.98 (3H, s), 3.89 (3H, s).
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