(±)-1-{8'-(tert-Butyl-diphenyl-silyloxy-meth-yl)-1',7'-dioxaspiro-[5.5]undecan-2'-yl}uridine.

The crystal structure of the title compound, C(30)H(38)N(2)O(5)Si, has been investigated to establish the relative stereochemistry at the spiro ring junction and the two anomeric centres. Each of the O atoms in the tetra-hydro-pyran rings adopts an axial position on the neighbouring ring. This bis--diaxial conformation is adopted, thus gaining maximum stablization from the anomeric effect. The silyl-protected hydroxy-methyl and uracil substituents adopt equatorial positions on their associated tetra-hydro-pyran rings, thereby minimizing unfavourable steric inter-actions. The dimeric (2'R*,6'R*,8'R*)- and (2'S*,6'S*,8'S*)-uridine units are connected to each other across crystallographic inversion centres via inter-molecular N-H⋯O hydrogen bonds.