Synthesis
The general procedure for the synthesis of 2-bromo-4-methoxybenzaldehyde from p-methoxybenzaldehyde is as follows:
Example 4: Scheme C1; n-Butyl lithium (n-BuLi, 1 equiv, 147 mmol, 59 mL, 2.5 M) was slowly added dropwise to an anhydrous tetrahydrofuran (THF, 80 mL) solution of trimethylethylenediamine (TMEDA, 1.1 equiv, 162 mmol, 17.0 g) under stirring at -20 °C. After 15 min, p-methoxybenzene formaldehyde (1 eq, 147 mmol, 20.0 g) and stirring was continued for 15 min, followed by dropwise addition of n-butyllithium (n-BuLi, 3 eq, 441 mmol, 176 mL, 2.5 M). The reaction mixture was stirred at 0 °C for 20 hours. The solution was cooled to -78 °C, carbon tetrabromide (2.7 eq, 397 mmol, 131.6 g) was added, and the solution was allowed to warm slowly to room temperature. A 10% aqueous hydrochloric acid solution was added and extracted with dichloromethane. The organic extracts were combined and washed sequentially with saturated aqueous sodium thiosulfate, water and brine. The organic phase was dried with anhydrous magnesium sulfate (MgSO4) and subsequently concentrated under vacuum. The residue was purified by silica gel column chromatography (eluent: heptane/ethyl acetate, 9:1) to afford the target compound C1.2 as a white solid (8 g, yield = 25%).
1H-NMR (δ, DMSO-D6): 3.89 (3H, s), 7.13 (1H, dd, J=8.7,2.4 Hz), 7.35 (1H, d, J=2.4 Hz), 7.83 (1H, d, J=8.7 Hz), 10.10 (1H, s) ppm.
References
[1] Tetrahedron, 2012, vol. 68, # 40, p. 8463 - 8471
[2] Chemical Communications, 2005, # 46, p. 5793 - 5795
[3] Organic and Biomolecular Chemistry, 2007, vol. 5, # 1, p. 143 - 150
[4] Organic Letters, 2011, vol. 13, # 14, p. 3686 - 3689
[5] Patent: WO2008/37784, 2008, A1. Location in patent: Page/Page column 37
