2-N-Benzyl-2,6-dideoxy-2,6-imino-3,4-O-isopropylidene-3-C-methyl-d-allononitrile

X-ray crystallography firmly established the relative stereochemistry of the title compound, C17H22N2O3. The absolute configuration was determined by use of 2-C-methyl-d-ribonolactone as the starting material. The compound exists as O—H⋯N hydrogen-bonded chains of molecules running parallel to the a-axis.

X-ray crystallography firmly established the relative stereochemistry of the title compound 4. The absolute configuration was determined by the use of 2-C-methyl-D-ribonolactone 1 as the starting material. The acetonide ring adopts an envelope conformation with C16 out of the plane and the piperidine ring adopts a chair conformation (Fig. 2).
The compound exists as O-H···N hydrogen-bonded chains of molecules running parallel to the a-axis (Fig. 3). Only classical hydrogen-bonding was considered.

Refinement
In the absence of significant anomalous scattering, Friedel pairs were merged and the absolute configuration was assigned from the starting material.
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.
The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-0.98, O-H = 0.82 Å) and U iso (H) (in the range 1.2-1.5 times U eq of the parent atom), after which the positions were refined with riding constraints.