2-O-Benzhydryl-3,4-(S)-O-benzylidene-d-lyxono-1,4-lactone

X-ray crystallography unequivocally showed that protection of the free hydroxyl group of 3,5-O-benzylidene-d-lyxono-1,4-lactone with diphenyldiazomethane proceeded with retention of configuration to give the title compound, C25H22O5. The crystal structure consists of layers of interlocked molecules lying parallel to the a axis.

X-ray crystallography unequivocally showed that protection of the free hydroxyl group of 3,5-O-benzylidene-d-lyxono-1,4lactone with diphenyldiazomethane proceeded with retention of configuration to give the title compound, C 25 H 22 O 5 . The crystal structure consists of layers of interlocked molecules lying parallel to the a axis.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: LH2567).

Comment
Carbohydrates are relatively inexpensive and are useful starting materials for the synthesis of small chiral molecules (Collins & Ferrier, 1995) and chiral building blocks (Draths et al., 1992). Much of their synthetic utility is however dependent on developing successful protecting group strategies. Diazodiphenylmethane has been found to be a useful protecting group in the synthesis of methyl 2,3,6-tri-O-methyl-[α]-D-glucopyranoside and kojibiose octa-acetate (Jackson et al., 1982), and monoalkylations of vicinal diols have been achieved with this reagent and other diaryldiazoalkanes with high regioselectivities (Petursson & Webber, 1982;Petursson et al., 2007;Petursson, 2003;Petursson, 2001). This is of particular interest as the reaction is carried out under neutral conditions. The utility of the benzhydryl group as a protecting group in carbohydrate chemistry has here been demonstrated with the reaction of 3,5-O-benzylidene-D-lyxono-1,4-lactone 1 with diphenyldiazomethane ( Fig. 1). Such lactones are susceptible to epimerization at C-2; however x-ray crystallography unequivocally showed that this had not occurred and the protection had proceeded with retention of stereochemistry (Fig. 2). The crystal structure consists of layers of interlocked molecules ( Fig. 3 and Fig. 4), lying parallel to the a-axis. There are no short range intermolecular interactions and no unusual bond lengths or angles. The absolute configuration was determined by the use of D-lyxonolactone as the starting material.

Refinement
In the absence of significant anomalous scattering, Friedel pairs were merged and the absolute configuration was assigned from the starting material.
The relatively large ratio of minimum to maximum corrections applied in the multiscan process (1:1.5) reflect changes in the illuminated volume of the crystal. Changes in illuminated volume were kept to a minimum, and were taken into account (Görbitz, 1999) by the multi-scan inter-frame scaling (DENZO/SCALEPACK, Otwinowski & Minor, 1997).
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 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.