5-Bromovanillin

Add 15.2g vanillin and 17.6g Br₂ to 75ml AcOH, let the solution stir 1 h. Pour out the solution in 250mL ice-water. filter off the product. Dry and recrystallise from ethanol. mp. 162°C. TLC R_f 0.47 EtOAc:Hexane 1:1

3,5-Dimethoxy-4-Hydroxybenzaldehyde (Syringaldehyde)

In a two-necked round-bottomed flask equipped with a Claisen, and a thermomether into the solution, is dissolved 4.9g sodium metal in 100mL dry methanol. After distilling off 30ml methanol, a solution of 17.9g bromovanillin and 3g CuBr in 50mL DMF is added in one portion. The distillation is continued until the reaction mixture reaches 100°C (takes app. 1-1.5 h. total methanol distilled off is 80mL). The reaction mixture is poured into 200mL 3M HCL/ice, extracted with 2x75mL EtOAc, the EtOAc is washed with 2x50mL water, dried with MgSO₄ and evaporated, mp 108°C (rextal. from ethanol) TLC R_f 0.35 EtOAc:Hexane 1:1

3,4,5-trimethoxybenzaldehyde

10g 3,5-dimethoxy-4-hydroxy-benzaldehyde, 13.5g K₂CO₃ and 8.3g dimethylsulfate is dissolved in 80mL dry DMF, the solution is stirred for 2h and then poured into 800mL ice/water, the product is filtered off and xtalised from cyclohexane.

All reactions gives over 80% yield after recrystallization.

The condensation of 3,4,5-Trimethoxybenzaldehyde with nitromethane (with cat. ethylenediammonium diacetate) gives ~30% yield.