合成路线1

The intermediate 3-cyclohexyl-2(R)-methylpropionyl chloride (XVIII) has been obtained as follows: The reaction of 4(S)-isopropyloxazolidin-2-one (XIX) with propionyl chloride (XX) by means of BuLi in THF gives 4(S)-isopropyl-3-propionyloxazolidin-2-one (XXI), which is condensed with benzyl bromide (XXII) by means of LHMDS in THF yielding 4(S)-isopropyl-3-(2(R)-methyl-3-phenylpropionyl)oxazolidin-2-one (XXIII). The oxidative cleavage of (XXIII) with H2O2 in THF/water affords 2(R)-methyl-3-phenylpropionic acid (XXIV), which is hydrogenated with H2 over alumina providing 3-cyclohexyl-2(R)-methylpropionic acid (XXV). Finally, this compound is treated with oxalyl chloride in DMF to afford the desired intermediate 3-cyclohexyl-2(R)-methylpropionyl chloride (XVIII).