合成路线1

The intermediate N-Boc-amino acid (VII) was synthesized as shown in Scheme 25409101a. Treatment of 3-(tert-butoxycarbonylamino)-3-methylbutanoic acid (I) with ethyl chloroformate and Et3N, followed by reduction of the resulting mixed anhydride (II) with LiBH4, provided alcohol (III). Then, oxidation of (III) under Swern conditions yielded aldehyde (IV). Subsequent Horner-Emmons condensation of (IV) with triethyl phosphonoacetate (V) in the presence of potassium tert-butoxide gave ester (VI), which was saponified with LiOH to provide the required carboxylic acid (VII).