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Stage #1: With lithium triethylborohydride In tetrahydrofuran at -40 - 20℃; for 1.5 h; Stage #2: With citric acid In tetrahydrofuran; water
Reference Example 29(l,l-Dimethyl-2-oxo-ethyl)-carbamic acid tert-butyl ester <n="71"/>To a solution of [l-(methoxy-methyl-carbamoyl)-l-methyl-ethyl]-carbamic acid tert- butyl ester (8.4 g, 34.1 mmol) in anhydrous THF (150 mL) was added Super Hydride.(R). dropwise at - 40 °C. The resulting mixture was allowed to warm to RT over 30 min, and then stirred at RT for 1 h. An aqueous solution of citric acid was added, the mixture was concentrated in vacuo and the resulting residue partitioned between water and EtOAc. The organic layer was separated and washed with brine, then dried (MgSO4) and concentrated in vacuo. The resultant residue was purified by column chromatography to give the title compound as a white solid (4.36 g, 68 percent). 1H NMR (400 MHz, CDCl3): δ 1.33 (s, 6 H), 1.44 (s, 9 H), 4.96 (bs, 1 H)and 9.43 (s, 1 H).
Reference：
[1] Patent: WO2009/53716, 2009, A1, . Location in patent: Page/Page column 69-70
[2] Patent: WO2005/19174, 2005, A1, . Location in patent: Page/Page column 52
[3] Organic and Biomolecular Chemistry, 2011, vol. 9, # 19, p. 6566 - 6574
[4] Patent: US2012/322811, 2012, A1, . Location in patent: Page/Page column 18
[5] Journal of Organic Chemistry, 2014, vol. 79, # 3, p. 1254 - 1264
Reference Example 29(l,l-Dimethyl-2-oxo-ethyl)-carbamic acid tert-butyl ester <n="71"/>To a solution of [l-(methoxy-methyl-carbamoyl)-l-methyl-ethyl]-carbamic acid tert- butyl ester (8.4 g, 34.1 mmol) in anhydrous THF (150 mL) was added Super Hydride dropwise at - 40 C. The resulting mixture was allowed to warm to RT over 30 min, and then stirred at RT for 1 h. An aqueous solution of citric acid was added, the mixture was concentrated in vacuo and the resulting residue partitioned between water and EtOAc. The organic layer was separated and washed with brine, then dried (MgSO4) and concentrated in vacuo. The resultant residue was purified by column chromatography to give the title compound as a white solid (4.36 g, 68 %). 1H NMR (400 MHz, CDCl3): delta 1.33 (s, 6 H), 1.44 (s, 9 H), 4.96 (bs, 1 H)and 9.43 (s, 1 H).
With lithium aluminium tetrahydride; In diethyl ether; at -50 - 0℃; for 3h;
To a solution OF N-BOC-2-AMINO-N-METHOXY-N-METHYLISOBUTYRAMIDE (2.94 g, 11.9 mmol) in diethyl ether (70 ml) at-50 C was added slowly IN LIAIH4/DIETHYL ether (24 ml). Stirring was continued for 1 h and the reaction mixture was allowed to warm up to 0 C over 2 h. The mixture was cooled TO-50 C, quenched carefully with ethyl acetate (5 ml), stirred for additional 10 min, hydrolyzed with 0.5 M aqueous HCl (50 ml), and warmed up to room temperature. 1M Aqueous HCl was added until the solution became clear. The aqueous layer was extracted with diethyl ether (100 ml). The combined organic layers were finally with brine (200 ml), dried over sodium sulfate, and concentrated in vacuo providing crude N-BOC-2- amino-2-methyl-propionaldehyde (1.45 g) as colorless oil.
With lithium aluminium tetrahydride; In diethyl ether; at -40℃; for 0.0833333h;
Lithium aluminum hydride (7.8 g) was added to a stirred solution of [1-(methoxy-methyl-carbamoyl)-1-methyl-ethyl]-carbamic acid tert-butyl ester (compound L; 42.0 g) in dry diethyl ether (1.5 L) at -40 C. Then stirred at that temperature for about 5 min. Excess LiAlH4 was quenched with a solution of potassium hydrogen sulfate in water. The resulting mixture was partitioned between EtOAc and 3M aqueous HCl. The organic layer was washed with sat. aqueous NaHCO3, dried over Na2SO4, filtered, and concentrated in vacuo to afford (1,1-dimethyl-2-oxo-ethyl)-carbamic acid tert-butyl ester (compound M; 29 g) sufficiently pure for the next step.
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