Deuterium-labeling experiments deprotonation

Competitive with -deprotonation, a-deprotonation furnishes the carbenoid-type oxiranyl anion species 10. In selected cases anion formation has been established to be a reversible process by deuterium-labeling experiments. As opposed to -deprotonation which gives only allylic alcohols, a-deprotonation can give rise to a variety of products as summarized in Scheme 4. This behavior will be further discussed in Section V. Some... 

It is interesting to note that no reaction is observed with oxirane 72a if the hydroxyl group is protected. Moreover, whereas deuterium labeling experiments indicate a clean /3-deprotonation process for both oxiranes 69 and 72a, the same enantiomer of base 71 furnishes the corresponding allylic alcohols 70 and 73a with the opposite absolute configurations (Scheme 30 vs. 31). The same studies on vicinal disubstituted analogues 72b,c showed that both the sense and the level of enantioselectivity are unchanged, which... 

For this reason, the only literature example regarding the use of nitroalkenes as Michael acceptors in enantioselective Michael reactions under PTC conditions is related to the use of oxindoles as pro-nucleophiles (Scheme 5.31). In this context, using deuterium labeling experiments, it was found that oxindoles underwent fast deprotonation in neutral aqueous media only in the... 

Reaction of l,2 5,6-di-0-isopropylidene-3-0-triflyl-a-D-glucofuranose with methyllithium gives the corresponding glycal (double bond in the 3,4-position) by an apparent E-2 elimination. However, deuterium labelling experiments suggest the mechanism first involves deprotonation at C-3 followed by a 1,2-hydride shift from C-4->C-3 and hence to product. ... 

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