合成路线1

Isobutyraldehyde (I) was condensed with vinylmagnesium bromide (II) to provide allylic alcohol (III).Transesterification with diethyl malonate (IV) in the presence of titanium ethoxide, followed by Claisen rearrangement at 190 C gave malonate (V). Subsequent basic hydrolysis of (V) with concomitant decarboxylation yielded 6-methyl-4-heptenoic acid (VI). This was transformed to the corresponding acid chloride by means of SOCl2 and then coupled with (1R,2R)-(-)-pseudoephedrine (VII) to produce the chiral amide (VIII). Alkylation of the dianion of (VIII) with 4-methylbenzyl bromide (IX) in the presence of LiCl afforded the benzylated compound (X). Further treatment of (X) with N-bromosuccinimide and AcOH in THF generated the bromolactone (XI). The bromo group of (XI) was then displaced with NaN3, and the resulting azide (XII) was hydrogenated in the presence of di-tert-butyl dicarbonate to provide carbamate (XIII). Basic hydrolysis of the lactone (XIII) gave hydroxyacid (XIV), which was oxidized to ketoacid (XV) by means of N-methylmorpholine-N-oxide and tetrapropyl ammonium perruthenate.