Water → 5,5-Dimethyl-3-formyl-hexanoic acid methyl ester

In a three necked flask fitted with a Dean-Stark apparatus under argon, a solution of diisobutylamine (4.62 ml from Acros), 4,4-dimethyl pentanal 362 (2.5 g, 0.021 mol.) in toluene (20 ml) is heated at 130° C. for 2 h and water is extracted. The yellow solution is cooled down to room temperature and methyl bromoacetate (3.7 g, 0.024 mol.) is added in one time. The pink solution is stirred at room temperature overnight and 1 h at 90° C. Water (10 ml) is added at this temperature and after 1 h, the solution is cooled down to room temperature. The organic layer is washed with HCl 1N, saturated aqueous sodium bicarbonate, dried over magnesium sulfate, filtered and evaporated to afford an oil which is distilled under reduced pressure (1 mmHg) to afford 5,5-dimethyl-3-formyl-hexanoic acid methyl ester 361 as a liquid (1.1 g, 0.05 mol, Teb (1 mmHg): 69-71° C.). The aldehyde esters are then used in the reductive amination step. Alternatively, alkylation with ethyl bromoacetate can be conducted in the presence of toluene-acetonitrile 1/1 (v/v) as solvent. The final aldehyde can also be distilled under reduced pressure.