Restoring exo-anomeric effect in carbasugars

The VAE has also been used to generate nitrosoalkenes from a-chloro ketoximes and to accelerate Claisen rearrangements of appropriately substituted substrates. An interesting example of the remote effect on reactivity was found in the epoxidation of 4-deoxypentenosides (4-DPs) by dimethyldioxirane (DMDO) where competing directing effects can be imposed by the anomeric and allylic substituents.  

Anomeric reactivity in radical reactions Effects are strongest for the formation of cationic centers but they are also significant for bonds stretching and breaking, including homolytic cleavage that leads to the formation of radicals next to the lone pair. As discussed earlier, stretched bonds are relatively strong acceptors (Chapter 9) and radicals form 2c,3e-bonds with adjacent lone pairs (Chapter 3). 

Oxygen atom activates the axial C-Hg bond (stereoelect ponies) 

Oxygen atom deactivates the equatorial C-Hg bond (hybridization - increased s-character in the C-H bond) 

Furthermore, the observed reactivity trends illustrated the interplay of anomeric effect with two other electronic factors described earlier in this book. In particular, the loss of activation associated with the poor lone pair/C-H overlap in the bicyclic system is an example Bredt s rule (restriction on jt-overlap at the bridgehead position) whereas the additional deactivation of is a consequence of Bent s rule. Because the 

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