An efficient organometallic approach to new carbocyclic nucleoside analogues.

[reaction: see text] A general synthetic approach to monoprotected carbocyclic nucleoside analogues, having the nucleobase attached to a 3-hydroxymethyl-4-trialkylsilyloxymethyl-cyclopent-2-en-1-yl scaffold, was developed. A (racemic) key intermediate was prepared by a cobalt-mediated Pauson-Khand reaction. In the course of the further synthesis, the introduction of the nucleobase was achieved with complete regio- and diastereoselectivity through a palladium-catalyzed allylic substitution.