Deoxyhydantocidin: Synthesis by base-catalyzed spiro cyclization and interconversion with the 1 '-epimer

Syntheses of the spiro nucleosides 2'-deoxyhydantocidin 3a and its 1'-epime r 3b are described. The newly developed route involves a Horner-Wads worth- Emmons condensation of the phosphonate 16 with the erythrose derivative 15 affording a mixture of six isomers which was fully assigned by NMR spectros copy. The mixture was directly converted into the final compounds in an eff icient base-catalyzed cyclization reaction. A base-catalyzed interconversio n between the two isomers was observed.