Dimethylformamide → 4-Chloro-2,6-dimethylbenzaldehyde

Dissolve 4-bromo-3,5-dimethyl chlorobenzene (6.5 g) in 50 mL anhydrous THF and cool to −78° C. (dry ice/acetone) under N2. Dropwise over 5 min add a solution of butyllithium (12.50 mL, 2.5M in hexanes) to the stirring solution of aryl bromide at −78° C. After 2 h, dropwise add anhydrous DMF (5.0 mL) to the orange/red reaction solution and allow to warn to ambient temperature overnight while stirring under N2. Evaporate the yellow solution down to a yellow oil and partition between H2O (100 mL) and CH2Cl2 (100 mL). Extract the aqueous layer once with CH2Cl2, then pool the organic layers and dry over Na2SO4, filter and evaporate down to 5.0 g of yellow oil. Use without further purification. LCMS=169.6 (MH+).