Precursors of sinefungin were prepared by chain extension of the blocked adenosine 5′-aldehyde 4 through a carbon-carbon bond to C-5’. Bond formation was accomplished with variously functionalized stabilized ylides. Employment of 2-oxo-3-(triphenylphosphoranylidene)tetrahydrofuran (7) gave a nucleoside lactone (8) which was converted in several steps to a C-6’ carboxylic acid (10c). A Curtius rearrangement of this acid, quenching with benzyl alcohol, allowed the introduction of a C-6’ amino group, blocked as a urethane (11a). The chain-ending (C-8’) alcohol was converted to a leaving group and displaced by azide ion and dibenzyl sodiomalonate. © 1983, American Chemical Society. All rights reserved.