2-Methyl-4-bromo-aniline (0.637 g, 3.427 mmol) was dissolved in DCE (15 mL); to this solution was transferred a solution of 4-(2-oxo-ethyl)-piperidine-1,4-dicarboxylic acid 1-tert-butyl ester 4-ethyl ester (1.03 g, 3.425 mmol) in DCE (35 mL). The flask was submerged in a water bath at rt. To this clear solution was then added acetic acid (0.647 g, 10.8 mmol, 3.1 equiv), followed by addition of powder NaBH(OAc)3 (2.18 g, 10.3 mmol, 3 equiv.) under N2 at r.t. The yellowish milky suspension was stirred at r.t. overnight. LC/MS showed m/z 469/471 at t=4.930 min. along with small amount of aniline sm at 2.103 (186/188). TLC (5% of MeOH in DCM) showed no SM. of aldehyde, but aniline. The reaction was diluted with DCM (20 mL), cooled to ice-water bath, and quenched with 10 mL of 1N NH4OH. The two layers were separated, and the aqueous layer was extracted with DCM (15 mL×3). The combined DCM extracts were washed with sodium bicarbonate (10 mL), and brine (10 mL), dried (anhydrous potassium carbonate), filtered, and concentrated. The product was purified on a 40 g-silica gel column eluted with 0-2% of MeOH in DCM to get 0.65 g (41%) of the title compound as an oil.
