The ring-closing metathesis method is applied in the construction of confor
mationally restricted bicyclic nucleosides. From diacetone-D-glucose, the u
nsaturated bicyclic carbohydrate derivative 11 is efficiently obtained thro
ugh two vinyl group Grignard additions, subsequent metathesis of the double
bonds, and resolution of the stereochemistry by an oxidation/reduction rea
ction sequence. Two separate routes differing in the 3-O-protecting group a
re compared. Thus, an additional protecting step improves the yields signif
icantly. Standard conversions of 11 give the bicyclic nucleoside 22 contain
ing an olefinic moiety with a high potential for further functionalisation.
As examples, two simple bicyclic ribo-nucleoside analogues 4 and 5, which
are restricted to the unusual South-type conformations, are synthesised.