Electron-withdrawing groups ketyl radicals

Alternatively, the electron-withdrawing properties of the a-heteroatom and its ability to coordinate Sml2 may facilitate reduction of the ester carbonyl group and formation of ketyl radicals 37 (Scheme 4.22). Once the activating heteroatom group has been removed, no further ester reduction is possible. A similar mechanism is possible for the reduction of a-heteroatom-substituted amides. 

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