Synthesis of Gabosine A and N from Ribose by the Use of Ring-Closing Metathesis

A concise synthetic route is described for the synthesis of gabosine A and N. The key step uses a zinc-mediated tandem reaction where methyl 5-deoxy-5-iodo-2,3-O-isopropylidene-beta-D-ribofuranoside is fragmented to give an unsaturated aldehyde which is allylated in the same pot with 3-benzoyloxy-2-methylallyl bromide. The functionalized octa-1,7-diene, thus obtained, is converted into the six-membered gabosine skeleton by ring-closing olefin metathesis. Subsequent protective group manipulations and oxidation gives rise to gabosine N in a total of 8 steps from ribose while the synthesis of gabosine A employs an additional step for inverting a secondary hydroxy group. (