Methyl N-(triethylammoniosulfonyl)carbamate → Ethyl (4S)-2-{(1R)-1-[2-(tert-butoxy)-2-oxoethyl]4-cyclohexylbutyl}-4,5-dihydro-1,3-oxazole-4-carboxylate

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Reaction Steps

A solution of tert-butyl (3R)-6-cyclohexyl-3-({[(1S)-2-ethoxy-1-(hydroxymethyl)-2-oxoethyl]amino}carbonyl)hexanoate (Preparation 30) (4.14 g, 10 mmol) in anhydrous tetrahydrofuran (40 ml) was treated with (methoxycarbonylsulfamoyl)triethylammonium hydroxide, inner salt [Burgess Reagent] (2.62 g, 11 mmol) and the resulting mixture was heated under reflux under a nitrogen atmosphere for 1 hour. The solvent was removed under reduced pressure and the residue purified by column chromatography on silica gel eluting with a gradient system of pentane:ethyl acetate (80:20) to (50:50) to afford the title compound as a colourless oil (3.10)

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