2-Azido-3,4;6,7-di-O-isopropylidene-α-d-glycero-d-talo-heptopyranose

In the title compound, C13H21N3O6, the six-membered ring adopts a twist-boat conformation with the azide group in the bowsprit position. The azide group is disordered over two sets of sites in a 0.642 (10):0.358 (10) ratio. The crystal structure consists of O—H⋯O hydrogen-bonded trimer units. The absolute configuration was determined from the use of d-mannose as the starting material.

In the title compound, C 13 H 21 N 3 O 6 , the six-membered ring adopts a twist-boat conformation with the azide group in the bowsprit position. The azide group is disordered over two sets of sites in a 0.642 (10):0.358 (10) ratio. The crystal structure consists of O-HÁ Á ÁO hydrogen-bonded trimer units. The absolute configuration was determined from the use of dmannose as the starting material.
A Kiliani cyanide reaction on diacetone mannose gave the lactone diacetonide 1 (Beacham et al., 1991;Myerscough et al., 1992). Esterification of 1 ( Fig. 1) with triflic anhydride in pyridine followed by reaction with sodium azide in DMF gave the azide 2 with retention of configuration at C2; the stereochemistry of 2 was established by X-ray crystallographic analysis (Bruce et al., 1990). Reduction of the lactone 2 afforded the lactol 3, a key intermediate for the synthesis of four of the possible sixteen iminoheptitols 4 by Izumoring techniques. The reported crystal structure of 3 determines the configuration of both the azide at C2 and the anomeric position.
The X-ray structure shows that the six-membered ring in the title compound adopts a twist boat conformation with the azide in the bowsprit position and the anomeric alcohol group in the less hindered α-position (Fig. 2). There is significant disorder in the structure with the azide occupying two possible sites. The compound exists as repeating hydrogen bonded trimer units (Fig.3, Fig. 4, Fig. 5). The absolute configuration was determined from the use of D-mannose as the starting material. 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 D-mannose. 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.