(1R,3S,4R,4aS,7R,7aS,10R,12aR)-3-Azido-4,7,10-trimethyl-1,10-epidioxyperhydropyrano[4,3-j][1,2]benzodioxepine

In the title compound, C15H23N3O4, the six-membered pyran, cyclohexane and trioxane rings adopt chair, chair and boat conformations, respectively, while the seven-membered rings adopt distorted boat and very distorted chair conformations. In the crystal, adjacent molecules are connected by weak C—H⋯N and C—H⋯O interactions.

In the title compound, C 15 H 23 N 3 O 4 , the six-membered pyran, cyclohexane and trioxane rings adopt chair, chair and boat conformations, respectively, while the seven-membered rings adopt distorted boat and very distorted chair conformations. In the crystal, adjacent molecules are connected by weak C-HÁ Á ÁN and C-HÁ Á ÁO interactions.
The crystal structure of the title compound is given in Fig. 1. The bond lengths and angles in the title compound are found to have normal values with respect to highly related compounds Jasinski et al., 2008). The six membered rings A, B and C adopt chair, chair and boat conformations, respectively. In the crystal, adjacent molecules are connected by non-classical C-H···N and C-H···O hydrogen bonding, with the distance of 3.628 (6), 3.508 (5) and 3.535 (5) Å (Table   1), respectively.

Experimental
Trimethylchlorosilane (300 mmol, 38.1 ml) was added gradually to a solution of dihydroartemisinin (200 mmol, 56.8 g, diastereomeric mixture with R and S configuration at C(3)) and sodium azide (300 mmol, 19.5 g) in CH 2 Cl 2 (300 ml). Then sodium iodide (20 mmol, 3.0 g) was added to the reaction mixture at low temperature. The reaction mixture was stirred at room temperature for 28 h. The mixture was quenched with a saturated NaHCO 3 solution (100 ml) and diluted with CH 2 Cl 2 .
Two phases were separated and the organic phase was washed with brine, dried over MgSO 4 , filtered, and concentrated under reduced pressure. The crude mixture was purified by column chromatography (silica, 1%-5% EtOAc/hexanes) to furnish the product (94 mmol, 29.0 g) and it's diastereomer with R configuration at C(3). Colorless single crystals of the title compound was obtained in CH 2 Cl 2 solution after 10 days by slow evaporation at room temperature.

Special details
Experimental. We took dihydroartemisinin (mixture of 3R and 3S isomers of hydroxyl group) as the starting material in our experiment. During the course of synthesis, we got a mixture of two diastereomers with 3S and 3R and all other stereogenic centers are known and still in the configuration as they were in the starting compound. The mixture was separated by silica gel column chromatography and the title compound with 3S was crystallized under our conditions, while the other one (3R) was obtained as amorphous powder.
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance mat-