N-tert-Butoxycarbonyl-L-leucinal: Boc-L-leucinal. A 5-L, four-necked, round-bottomed flask is equipped with an efficient mechanical stirrer, a thermometer, a pressure-equalizing addition funnel, and an air-cooled condenser fitted with an argon blanket adapter. The flask is charged with lithium aluminum hydride (17.7 g, 0.44 mol) (Note 9), and 1.5 L of anhydrous ethyl ether (Note 10). The gray suspension is <stirred> at <room temperature> for <1 hr> or until most of the <solid> is finely dispersed. The flask is immersed in a dry ice–2-propanol bath and the suspension <cooled> to <−45°C>. A solution of the Boc-L-leucine N-methyl-O-methycarboxamide in 300 mL of anhydrous ethyl ether is placed in the addition funnel and added to the lithium aluminum hydride suspension in a <steady stream> (Note 11) while the reaction <temperature> is maintained −35° ± 3°C. The cooling bath is removed and the mixture is <stirred> and allowed to warm to +5°C. The mixture is once again <cooled> to <−35°C> and a solution of 96.4 g (0.71 mol) of potassium bisulfate (Note 12) in 265 mL of <deionized water> is placed is added slowly while the <temperature> is allowed to rise to −2° ± 3°C. <Cooling> is ceased and the mixture is <stirred> for <1 hr>. The reaction mixture is <filtered> through <a pad of Celite> (Note 13), eluting with 2 x 500 mL portions of ethyl ether and <washed> with 3 x 350 mL portions of 1 M hydrochloric acid, 2 x 350 mL portions of saturated aqueous sodium bicarbonate solution, and 350 mL of saturated sodium chloride solution. The <organic layer> was <evaporated> under <reduced pressure>.