合成路线1

2) Other chiral directors, such as (S,S)-1,2-dicyclohexylethane-1,2-diol (XII), have also been used. Thus, the trans-esterification of boronate (IV) with diol (XII) gives the cyclic boronate (XIII), which was submitted to the previously described homologation with dichloromethane and butyllithium in THF to the intermediate (XIV). The treatment of (XIV) with anhydrous ZnCl2 as before yields the corresponding 5-bromo-1-chloroboronate (XV), which is methylated with methylmagnesium bromide as before affording the 5-bromo-1-methylboronate (XVI). The oxidative cleavage of (XVI) with Na2CO3 and H2O2 in THF affords 6-bromohexan-2(R)-ol (XVII), which is finally condensed with 3,7-dimethylxanthine (X) by means of NaH in DMSO.