2-C-Methyl-3 , 4O-methylidene-D-arabinono-1 , 5-lactone

Until recently, only linear carbohydrate chirons have been available as scaffolds for the synthesis of complex synthetic targets (Lichtenthaler & Peters, 2004). However, the Kiliani cyanide reaction on ketohexoses (Hotchkiss et al., 2004; Soengas et al., 2005) affords versatile intermediates with carbon branches at C-2 of the sugar for the synthesis of imino sugars and complex sugar amino acids with non-linear carbon chains (Simone et al., 2005). The Kiliani reaction on hamamelose provides access to carbohydrates with a branch at C-3 (Parker, Watkin, Simone & Fleet, 2006).

The relative stereochemistry at C-2 of the title compound, C 7 H 10 O 5 , was determined by X-ray crystallographic analysis of the arabinonolactone, which adopts a boat conformation with a flagpole hydroxyl group. Its absolute configuration was determined by the use of d-erythronolactone as the starting material.

Comment
Until recently, only linear carbohydrate chirons have been available as scaffolds for the synthesis of complex synthetic targets (Lichtenthaler & Peters, 2004). However, the Kiliani cyanide reaction on ketohexoses (Hotchkiss et al., 2004;Soengas et al., 2005) affords versatile intermediates with carbon branches at C-2 of the sugar for the synthesis of imino sugars and complex sugar amino acids with non-linear carbon chains . The Kiliani reaction on hamamelose provides access to carbohydrates with a branch at C-3 (Parker, Watkin, Simone & Fleet, 2006).
In order to optimize the protecting group strategy for the synthesis of complex targets (and to investigate the diastereoselectivity of the Kiliani cyanide extension), the formaldehyde acetal of d-erythronolactone, (7), was treated with methyl magnesium bromide to give the 1-deoxy-d-ribulose, (8). The Kiliani reaction of (8) with sodium cyanide gave a single diastereomeric product, (9), as the only 1,5-lactone isolated . This paper shows, by X-ray crystallography, that the arabinonolactone, (9), was formed in this reaction with none of the epimeric ribono diastereomer, (10), isolated.
The X-ray crystal structure determination shows that (9) is in a boat conformation (Fig. 1). The formation of (9) with the smaller hydroxyl group in the flagpole position may be due to the alternative product, (10), having the larger methyl group in the more hindered flagpole environment. The potential of (9) as a chiron is under investigation.
In the crystal structure, intermolecular O-HÁ Á ÁO hydrogen bonds (Table 1) link the molecules into zigzag chains extending along the a axis (Fig. 2).

Experimental
The title arabinono-1,5-lactone, (9), was obtained     Table 1 Hydrogen-bond geometry (Å , ). The molecular structure of the title compound, with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as spheres of arbitrary radii.

Figure 2
The crystal packing, viewed down the a axis. Hydrogen bonds are shown as dashed lines.
were merged and the absolute configuration was assigned from the known starting material. All H atoms were located in a difference map, but those attached to C 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 0.93-98 Å , and O-H = 0.825 Å ) and isotropic displacement parameters [U iso (H) in the range 1.2-1.5U eq of the parent atom], after which they were refined with riding constraints.