合成路线1

A further procedure for the preparation of the key intermediate (XIII) utilized the chiral starting material (S)-4-benzyloxy-1,2-butanediol (XIX), easily accessible from (S)-malic acid. Inversion of the configuration of (XIX) was accomplished via formation of dimesylate (XX), followed by displacement with potassium acetate in refluxing Ac2O. The resultant diacetate (XXI) was hydrolyzed to the required (R)-diol (XXII) by treatment with K2CO3 in MeOH. Conversion of (XXII) into epoxide (XXIV) was performed through the benzylidene ketal (XXIII), following the reported procedure for the corresponding (S)-enantiomer. Copper(I)-catalyzed addition of 3-butenylmagnesium bromide (XXV) to epoxide (XXIV) furnished alcohol (XXVI), which was further protected as the benzyl ether (XXVII). Hydroboration of olefin (XXVII) with in situ generated disiamylborane, followed by oxidative work-up gave rise to the primary alcohol (XXVIII). This was oxidized with pyridinium dichromate to the carboxylic acid (XXIX), which was further esterified by means of methanolic HCl to afford ester (XXX). Then, catalytic hydrogenolysis of the di(benzyloxy) ester (XXX) yielded the target intermediate dihydroxyester (XIII).