Boc-L-alanine methyl ester → tert-butyl N-((2S)-1-oxopropan-2-yl)carbamate

Boc-L-alanine methyl ester (5.0 g, 24.6 mmol) was dissolved in dry toluene (150 ml) under an argon atmosphere and cooled in a dry ice-acetone bath. To this vigorously stirred solution was added a solution of diisobutylaluminumhydride (1.0 M in hexanes, 61.5 ml, 61.5 mmol), pre-cooled in a dry ice-acetone bath, via a transfer needle. After 6 minutes, the reaction was carefully quenched with methanol (4 ml) and the mixture allowed to warm to room temperature. The reaction mixture was poured into a separatory funnel containing 250 ml ether and 200 ml of ice cold 0.25 N hydrochloric acid. The layers were separated and the organic layer was washed with 0.25 N hydrochloric acid (3×80 ml) and brine (50 ml). The organic layer was dried over magnesium sulfate, filtered and concentrated using a rotary evaporator at ambient temperature. The residue was chromatographed using hexanes--30% ethyl-acetate to give Boc-L-alaninal. The compound may also be prepared by the technique described in Synthesis, 1983, pg. 676.