Synthesis
Ni(NO3)2-6H2O (12.6 g, 43.33 mmol) was dissolved in methanol (200 mL) in a 500 mL three-necked round bottom flask. To this solution was added 5-bromo-8-nitro-N-methylisoquinolinium iodide (33.33 g, 84.38 mmol). Subsequently, NaCNBH3 (10.6 g, 168.68 mmol) was added in batches. The reaction mixture was stirred at room temperature for 5 h. The progress of the reaction was monitored by thin layer chromatography (TLC) (unfolding agent ratio EtOAc:PE = 1:5). After completion of the reaction, the reaction solution was concentrated under reduced pressure using a rotary evaporator. The residue was dissolved in 800 mL of water and the pH was adjusted to 8-10 with 5% NaOH solution. after filtration, the aqueous phase was extracted twice with 800 mL of EtOAc, and the organic layers were combined and dried with Na2SO4. Finally, the residue was purified by column chromatography (eluent ratio EtOAc:PE = 1:5) to afford 19.3 g (83% yield) of 5-bromo-2-methyl-8-nitro-1,2,3,4-tetrahydroisoquinoline as a yellow solid.
References
[1] Patent: US2008/318941, 2008, A1. Location in patent: Page/Page column 23
[2] Patent: WO2009/23844, 2009, A2. Location in patent: Page/Page column 105-106
[3] Patent: US2008/200471, 2008, A1. Location in patent: Page/Page column 45; 46
[4] Patent: US2010/16297, 2010, A1. Location in patent: Page/Page column 25
[5] Patent: WO2010/21797, 2010, A1. Location in patent: Page/Page column 69
