Glycals chlorine addition

Other methods of introducing amino substituents at C-2 by glycal additions include the use of the (saltmen)Mn(N) complex and trifluoroacetic anhydride,51 and the photochemical addition of Ar-chloro-chloroacetamide.52 In both cases tri-O-acetyl-D-glucal gives 2-amino-2-deoxy-D-glucose adducts, in the former case with the hydroxyl group at C-l, and in the latter with chlorine which can be displaced by alkoxy at that position. 

The addition of chlorine azide to acetylated or benzylated glycals afforded different mixtures of stereo- and rcgioisomcrs, depending on the experimental conditions (in the dark, or under irradiation with a mercury lamp), since an ionic or a concerted mechanism of addition as well as... 

Halogenation at C-2. As above described monobromo exo-glycals are suitable substrates for palladium catalysed cross-coupling reactions. The direct reaction of monobrominated phosphoranes with lactones is not straightforward. However, the facile addition of chlorine to dichloroolefins 1 has been described some years ago. Thus halogenation of anomeric double seemed a viable process and bromi-nation of compounds 3 was examined. Considerable experimentation led to find the proper conditions which allowed the formation of brominated eoco-glycals from 3 (Scheme 5). 

The carbene addition on the double bond of dichloro exo-glycals was explored. Dichlorocarbene, easily obtained from chloroform in a two phases system, was found the most efficient reagent giving tetra-chlorocyclopropanes 51 in useful yields. Reduction of the chlorine-carbon bond was achieved using lithium aluminium hydride in THF providing the spirocyclopropanes 52 in good pelds (Scheme 15). 

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