Stereochemistry of carbohydrate derivatives. Part II. Addition of iodine azide to unsaturated sugars: the crystal structure of 6-azido-5,6-dideoxy-5-iodo-1,2-O-isopropylidene-β-L-idofuranose

Abstract

X-Ray crystallographic analysis has established that the product of the addition of iodine azide to 5,6-dideoxy-1,2-O-isopropylidene-α-D-xylo-hex-5-enofuranose (III) is 6-azido-5,6-dideoxy-5-iodo-1,2-O-isopropylidene-β-L-idofuranose (IV), by anti-Markovnikov addition to the sugar double bond. The trioxabicyclo[3,3,0]octane ring-system is in a ‘twin-envelope’ conformation, with C(4) and the acetal carbon atom, C(7), displaced by 0·7 and 0·45 Å from the planes of the other four atoms of their respective five-membered rings. The crystals of the adduct are monoclinic, space group P21, Z= 2, in a cell of dimensions a= 5·86, b= 10·20, c= 10·80 Å, β= 91·2°. The structure was established by Fourier and least-squares methods and the final value of R is 19·7% for 830 observed reflections.