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ABSTRACT:Entecavir (BMS-200475) was synthesized from 4-trimethylsilyl-3-butyn-2-one and acrolein. The key features of its preparation are: (i) a stereoselective boron-aldol reaction to afford the acyclic carbon skeleton of the methylenecylopentane moiety; (ii) its cyclization by a Cp 2 TiCl-catalyzed intramolecular radical addition of an epoxide to an alkyne; and (iii) the coupling with a purine derivative by a 2 Mitsunobu reaction.

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A new method is reported for the conversion of azido acids into lactams, via thioester formation and in situ azide reduction and cyclisation under high-dilution conditions; since the quantitative conversion of macrolactams to macrolactones has been shown to be feasible, this results in an indirect, alternative macrolactonisation procedure. Natural products containing carboxamide functions inaf.3 has shown that methods used to obtain medium-to-large medium and large rings are abundant, the most important size macrolides (heating of o-hydroxyacids with dibutyltin types being cyclic peptides and depsipeptides, macrolactamic oxide) cannot be applied to the preparation of analogous alkaloids, and ansamycins. 1 Syntheses of these compounds macrolactams. We report here a synthetic route to macrolacoften involve a macrolactamisation step which usually poses tams, starting from azido acids rather than protonated or some specific problems.2 In fact, the recent report of Steliou et deprotonated amino acids.