合成路线1

The intermediate gamma-butyrolactone (XXVIII) has been obtained as follows: Allylation of the imidazolidinone intermediate (V) with allyl bromide (XXI) and LiHMDS in THF gives the chiral intermediate (XXII), which by dihydroxylation and cleavage of the chiral auxiliary with OsO4 and NMMO in tert-butanol/acetone/water yields the lactone alcohol (XXIII). Oxidation of (XXIII) with NaIO4 and RuCl3 in CCl4/acetonitrile/water affords the carboxylic acid (XXIV), which by treatment with (COCl)2 in toluene provides the acyl chloride (XXV). Esterification of (XXV) with benzyl alcohol gives the corresponding benzyl ester as a diastereomeric mixture, from which the desired isomer (XXVI) is separated by flash chromatography. Hydrogenolysis of the benzyl ester (XXVI) with H2 over Pd/C in ethyl acetate yields the carboxylic acid (XXVII), which is treated with oxalyl chloride in toluene to afford the desired gamma-butyrolactone intermediate (XXVIII).