elimination. From iodomethylcyclopropanes to thiirane analogs

Taking into account the thiophilic properties of iodine, a very simple methodology to achieve 2 0,3 0-didehydro-2 0,3 0-dideoxy-b-nucleosides in high yield was performed, using mild, and inexpensive conditions, by means of the treatment of 2 0-deoxy-3 0,5 0dibenzoyl-2 0-iodo-b-nucleoside derivatives with NaHS. The process has shown to be highly dependent of the relative geometry between the iodine atom and the adjacent leaving group. In this way, different essays carried out with pyranose derivatives have concluded in no reaction when the vicinal groups to eliminate do not adopt a trans-diaxial disposition. In addition, the treatment of 2-iodomethyl-cyclopropane-1,1-dicarboxylic acid diethyl ester under the same conditions softly and readily leads to the obtention of a mixture of the expected 2-allyl-malonic acid diethyl ester (as the minor product) and the thiirane derivative 2-thiiranylmethylmalonic acid diethyl ester (as the major product). In this case, the responsible of the reaction progress are the nucleophilic properties of the sulfur atom rather than the thiophilic character of the iodine atom. 2004 Elsevier Ltd. All rights reserved. The synthesis of nucleoside analogs in which the sugar and/or the heterocyclic moiety have been modified have received much attention as a consequence of their general biological activity and the potential use of such molecules as antiviral and antineoplasic therapeutic agents. Particularly, 2 0,3 0-didehydro-2 0,3 0-dideoxy nucleoside derivatives constitute noteworthy compounds with anti-HIV activity, which compared with AZT display a lower toxicity toward bone marrow. Among the different methodologies used in the synthesis of the title compounds, they could be highlighted those employing 2 0-deoxy-5 or 2 0,3 0-dideoxynucleosides,6 2 0,3 0diprotected ribonucleosides (cyclic orthoester, cyclic thiocarbonate, bis-xanthate) or the more simple unprotected diol, 2,2 0-anhydro-nucleosides,10 and unsaturated acyclic nucleosides. Nevertheless, the most popular methodology is based on the use of 2 00040-4039/$ see front matter 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2004.11.087