[H-].[Al+3].[Li+].[H-].[H-].[H-].[C:7]([O:11][C:12](=[O:23])[NH:13][C:14]([C:17](=[O:22])N(OC)C)([CH3:16])[CH3:15])([CH3:10])([CH3:9])[CH3:8]>C(OCC)C>[C:7]([O:11][C:12](=[O:23])[NH:13][C:14]([CH3:16])([CH3:15])[CH:17]=[O:22])([CH3:10])([CH3:8])[CH3:9]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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