Dimethyl Sulfoxide → tert-butyl N-((2S)-1-oxobutan-2-yl)carbamate

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Under an atmosphere of argon, oxalyl chloride (7.01 g, 4.75 ml, 55.3 mmol, Eq: 1.00) was combined with CH2Cl2 (100 ml) to give a colorless solution. The reaction was cooled to −60° C. Then dimethyl sulfoxide (10.8 g, 9.8 ml, 138 mmol, Eq: 2.5) diluted in CH2Cl2 (20 ml) was added dropwise at −60° C. The reaction was stirred for 10 min at −60° C. Then (S)-tert-butyl-1-hydroxybutan-2-ylcarbamate (11.62 g, 55.3 mmol, Eq: 1.00) dissolved in 20 ml CH2Cl2 was added dropwise at −70° C. The reaction was allowed to warm to −40° C. for 10 min and then cooled to −70° C. again. A solution of triethylamine (15.7 g, 21.6 ml, 155 mmol, Eq: 2.8) in 20 ml CH2Cl2 was added dropwise. The reaction mixture was allowed to warm to room temperature over 2 hours. The reaction mixture was poured into 100 ml satd. sodium dihydrogenphosphate solution and extracted with ethyl acetate (2×150 mL). The organic layer was back-extracted with brine (1×50 mL). The organic layers were dried over Na2SO4 and concentrated in vacuo. The title compound was obtained as a light yellow oil (11.12 g, quant., MS (m/e)=188.2 [M+H+]).

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